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Ngs Coords.

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My co Cacher and myself are finding bench marks in the Sheep Hole Pass, California, area that are off the mark by 300 Ft or so using the coords given by NGS. We have been lucky so far with most of them in that the witness posts have survived and we walked to the post and found the bench mark. Others in the area are dead on. The bench marks that we are looking for are 1974 sets although some are much older, the 1974 sets seem to be the problem. We located the old Ivanhoe (1935 I think) and all the associated markers including the azimuth marker without any problem. Got any ideas? :angry:

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Note that there is a difference between coordinates that are listed as SCALED and those that are ADJUSTED. ADJUSTED coordinates are usually found on triangulation disks that are used for horizontal control. The ADJUSTED marks can be accurately found with a handheld GPS. SCALED coordinates are found on benchmarks that are used for vertical control. The best way to find the SCALED marks is to use your GPS to get close (within the 300 feet) and then use the description provided on the datasheets to find the actual mark.

Edited by 5Wishes

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Which begs the question, how useful is it to submit our handheld coordinates to the NGS, which may be much better than the SCALED coordinates but may not be good enough for surveying work. Is there a sense of 'zero-ing in' that's allowed?

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No Surveyor is going to use anything other than adjusted coordinates. And no Surveyor worth his salt would base his work on only one bench mark, he would use 2 or more to confrim the position.

 

Handheld GPS coordinates help locate the mark and are very useful.. 300 ft can seem like a mile if the area has changed a lot.

Edited by elcamino

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Handheld GPS coordinates help locate the mark and are very useful.. 300 ft can seem like a mile if the area has changed a lot.

Our thoughts exactly. Handheld coordinates are useful for scaled positions. In fact, I have already seen a few datasheets that included handheld coordinates submitted by geocachers.

 

-Casey-

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Does that mean?

 

You would like handheld,fairly good averaged position of these marks added to the data sheet.

What about reference marks and azimuths?

 

Or should this go in the FAQ.

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Does that mean?

 

You would like handheld,fairly good averaged position of these marks added to the data sheet.

What about reference marks and azimuths?

 

Or should this go in the FAQ.

The ONLY time where handheld coordinates would be useful/appropriate are in cases of benchmarks (i.e. verticle control points) that have a SCALED LAT/LONG. If the horizontal location is not SCALED, handheld coordinates are not much use.

 

-Casey-

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Would it be appropriate to provide hand held coordinates of points that help to get to the mark, for example, coordinates of where a dirt road to the mark meets a major paved road, or coordinates of a good place to park?

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Would it be appropriate to provide hand held coordinates of points that help to get to the mark, for example, coordinates of where a dirt road to the mark meets a major paved road, or coordinates of a good place to park?

That is an interesting idea. For the time being I am going to say no. My reason being is that lat/long coordinates have never been part of a description before. But I will talk to a few people around here to see if there is any interest.

 

-Casey-

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Would it be appropriate to provide hand held coordinates of points that help to get to the mark, for example, coordinates of where a dirt road to the mark meets a major paved road, or coordinates of a good place to park?

That is an interesting idea. For the time being I am going to say no. My reason being is that lat/long coordinates have never been part of a description before. But I will talk to a few people around here to see if there is any interest.

 

-Casey-

It would come in Handy in the Rural enviroment here.

 

Just an example not coordinate correct.

and all caps

 

Instead of saying form Elsey go .50 mi.North to the wagon track trail ,continue west .75 mi to a track road follow track road to..........station on left .

 

 

Form Elsey go .50 mi.North to the wagon track trail (36* 54'22"-093* 48' 12") continue west .75 mi to a track road

(36* 54' 09"-093* 49' 12") follow track road to.......... station on left

Edited by GEO*Trailblazer 1

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If you have decent coordinates for the mark, I don't see that you usually need to worry about the "to reach" description at all, much less coordinates for locations along the way. Just get within some yards of the coordinates by any legal route, and then look for things to measure from.

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If you have decent coordinates for the mark, I don't see that you usually need to worry about the "to reach" description at all, much less coordinates for locations along the way.  Just get within some yards of the coordinates by any legal route, and then look for things to measure from.

I disagree. I don't use the 'to reach' directions very often, but many is the time that I wish I had. Especially in rural areas where landmarks can change appreciably over the decades (e.g. the "6-inch gum tree" that's now twice that size), I can certainly see there will be instances when the coordinates will be helpful.

 

Having said that, I also believe there will be many instances where coordinate will be entirely superfluous, such as in built-up areas where the 'to reach' directions are along named or numbered streets.

 

-ArtMan-

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299792458 Posted on Feb 28 2005, 02:26 PM

Would it be appropriate to provide hand held coordinates of points that help to get to the mark, for example, coordinates of where a dirt road to the mark meets a major paved road, or coordinates of a good place to park?

I submitted such a report to the NGS today for this PID. There's a fire road that goes into a small park. At one point on this road, there is a very small foot trail heading uphill. It is the way to take to get to the mark. So, we shall see how the report is entered. :lol:

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Today I entered a list of recent marks to the NGS. A couple had reports in 2004, the same as the year when I found the marks. Since they are scaled marks, I got Lat-Lon readings on them. Even though it was not a year since the most recent logs (which were just 'found as described'), I submitted the reports anyway, since I included the coordinates.

 

Do coordinates by themselves constitute a sufficiently useful addition to a to-reach within a year of the last report? We shall see....

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Blackdog,

 

Yes Your contribution will be very helpful to future seekers of that station, more so if it was particularly difficult to find with the description that it had. What you shall see, is your update, as you wrote it, in your own hand. and it will be there for the next several hundred years unless someone destroys the station and physically returns the remains to an NGS Geodetic advisor, in which case it may be removed from the database.

 

As a Surveyor, you will have just carved off a bunch of time I'll spend hunting it. I now could add the coordinate to my equipment and run a basic GO TO in order to find it, and by rights I should walk right up on it.

 

As an aside, yet worth reminding all other readers who may not yet know or realize, the practice of adding the GPS Coordinates which you got when visiting a Station is really only necessary for Vertical control Stations, NOT the Horizontal ones. The datasheet will tell you which kind you are working with, and please submit the data in Degree Minute and Second format which is standard to the format used with the datasheet and surveying. Thanks!

 

Rob

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Is there a standard typographic convention for entering the coordinates? We're somewhat hampered by the limitations imposed by NGS: you can use the double quote (") or degree (°) characters.

 

I've been entering in this format: N39d 34m 09.3s, W078d 13m 34.0s It's a little clunky, but it's unambiguous. (I use lower case, even though I know the published data sheets will be all upper case.)

 

Thoughts, anyone?

 

-ArtMan-

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I wrote this:

 

Handheld GPS coordinates are N 39 34 09 W 78 13 34

 

I think it is pretty much like what's on the datasheets except they put the N and W after the values rather than before.

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I find BDT's simple format agreeable, but would think it should be reported to 0.1 second, since your handheld on a good day is quite a bit better than a whole second.

 

BH

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Yes! The idiot factor came into play here. :ninja:

After my last post, I thought - why DID I round to the nearest second anyway? (I did all the measurements using DDD MM.MMM, so I had to calculate the seconds.)

 

Anyway, I just sent an email to Deb with the correct precision to 0.1 seconds for those PIDs where I entered coordinates (12 of them) last night.

 

I hope she or someone can catch up to my inputs to correct them, since it will take about 50 feet off the margin of error.

 

So, I come back here and sure enough, someone caught my error right away! :ninja:

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I have noticed in the last few days that the NGS scaled coordinates in this area agree with my handheld coordinates in ddd mm ss.s format if you drop the tenths of seconds. That is, not rounding, but simply dropping the tenths. That would account for almost all of the marks being north and/or west of the published scaled coordinates.

 

To wit: MG0634 (E 76)

 

My handheld coordinates this afternoon were: N 41 56 40.5 W 091 38 12.7

The Datasheet has: N 41 56 40 W 091 38 12

 

I would have to recheck, but I do not think I have found any benchmarks with scaled coordinates that were not north and/or west of the coordinates on the NGS datasheet. I have found a couple where my handheld coordinates showed the longitude as 0.2 seconds east of the published value. That may be explained by the margin of error in the GPSr, as I believe 0.2 seconds of longitude to be about 15 feet at this latitude.

 

Add to that error bias, that Groundspeak has some errors in converting to dd mm.mmm format.

 

Again with MG0634 (E 76)

 

NGS Datasheet: N 41 56 40 W 091 38 12

Groundspeak: N 41 56.667 W 091 38.183

 

Of course, 40 sec. = .667

 

But 12 seconds = 0.200 min rather than .183

 

In fact, .183 = 11/60. Hence, the Groundpeak longitude in this instance is over 1 second less than actual.

 

So the proper conversion from the datasheet to coordinates in DD MM.MMM are N 41 56.667 W 091 38.200.

 

I have not investigated if Groundspeak errors have any directional bias.

Edited by GH55

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The error is not in Groundspeak.

 

I checked some PIDs. Some were off in the W and one was off in the N, and one was OK.

 

In every case, when I'd click on "view original datasheet", the difference was shown to be in the NGS pages!

 

Perhaps there was a major adjustment since the time that Groundspeak got their data from the NGS.

 

Two examples are: tr0616 and ql0364.

Edited by Black Dog Trackers

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Hey All,

 

I Have always submitted mine in the same manner they are printed on the official datasheet; if the datasheet says it like this:

 

NAD 83(1986)- 47 40 07. (N) 122 24 06. (W) SCALED

 

So if there is an improvement to the datasheet that I can make, I annotate it as such:

 

WAAS CORRECTED NAD 83 GPS COORDINATES:

47 40 59.3(N) 122 23 11.7(W)

 

I just stay with the format on the datasheet so the thinking and interpretation remain the same. If I do not get WAAS lock then I do not say I did. I never use any other Datum or formats so there is no risk of conversion error on the part of myself or and other users who would have to field convert later.

 

I just add that paragraph to my recovery report. Thats it. I do it as a separate paragraph so as to set it apart from other forms of description.

 

I give the tenth of a second too, as without it, the update is not a lot better than scaled. Closer, but not as tight as it could be. In an ugly situation that tenth can be just the trick to find you need, and is the difference between give or take 5 and 50 feet, depending on where you are standing. We all know there are plenty of places to lose a Station in a 50 foot stretch, eh?

 

My .02.

 

Rob

Edited by evenfall

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Replying to Blackdog on the Maybe there was a major adjustment... Well, you are correct. The numbers do change if there is a way to improve upon them. In fact, adjustments to various areas and States are always happening. This is why you see NAD 83 (1986) or NAD 83 (1999) or what ever year that may be in parenthesis after the NAD 83 designation.

 

Each new year which is more recent than the last will be more precise and the superseded data should be noted on the page in it's appropriate area.

 

I hold no disregard for the geocaching.com copy of the database, and it works fine for simply playing the game, but The NGS website really is the best source to use for Datasheets and Information. So many things are constantly being done to the NSRS by so many contributors that barely a day goes by without something changing... Somewhere someone is working on the next Geoid model or is doing a major adjustment, or what have you, Maybe even correcting a scaled location... :-)

 

Rob

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If it is an adjustment issue, it is very different between scaled marks and adjusted marks.

 

I checked several (about 20) random PIDs (using the benchmark gallery). The horizontal coordinates of some were adjusted and some were scaled.

 

All but one of the adjusted ones were identical to 0.00001 seconds. The one that changed was AB5482, and that one changed by only about 0.001 second in both coordinates. The number in parentheses was different for this one station - 1990 vs. 1999.

 

The date (in parentheses) next to NAD 83 was, for some reason, 1986 or 1983 for all the scaled marks and in the 1990s for all the adjusted marks. However, in every case I saw except for AB5482, both versions ("view original datashsheet" and the current NGS data) had the same date in parentheses as each other.

 

It seems odd that the scaled marks would often change by a whole second, while all but one of the horizontally adjusted marks didn't change even in the 5th decimal place!

 

I imagine that the scaled marks and the adjusted marks are not adjusted together.

 

Something fairly large must've been done to the scaled marks' adjustment net, if it is simply an adjustment issue with them.

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I imagine that the scaled marks and the adjusted marks are not adjusted together.

 

Scaled marks are never adjusted. Scaled locations and or elevations are given as aide in locating the mark and planning a survey. The scaled position is only as good as the person who scaled it.

 

Today we have handheld GPSr to get very good positions but back in the old days, all the recon team did was mark the location on a USGS quad map when they set it or found it, take a ruler and interpolate the positions. Thats why they say, + or - 6 seconds accuracy. All the scaled postion is designed to do it to get you in the ball park, from there you have to find your own seat.

Edited by elcamino

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Well, something changed, apparently on the NGS side. Relatively few scaled PIDs show zero difference and it seems that more show a difference in W than N. The difference in the sample was always either 1 degree or 0. I don't see how some coordinates would change by a whole second and others would not.

 

A mystery. Not particularly important, I suppose. Just another reason for us to submit mark recoveries with coordinates for scaled marks to the nearest 1/10 second. B)

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I've logged coordinates on the marks I've reported to the NGS (my rule is finds only, and must have not been logged in the last 7 years). Personally, I take the waypoint measurement in WGS-84, and put those coordinates in the description marked as WGS-84 coordinates. Why? Two reasons:

 

#1) I don't trust myself to do a NAD-83 conversion, and I have no idea of the margin of error of the GPS is doing the conversion. Since it works internally with WGS-84 I figure another handheld GPS will always find the same spot.

 

#2) Since they are not survey grade observations and are in the description I feel the most likely thing someone will do is enter a mark in a handheld GPS or a car GPS and use some sort of "take me there" function to get in the general area. A few handheld units, and many car units will only let you enter WGS-84 coordinates. If someone ran into that problem there would be another conversion possibly introducing more error.

 

I also always take at least a 5 minute average with the GPS sitting on the benchmark. Sometimes more if I'm taking pictures and stuff. I also make sure the GPS unit reports < 5ft estimated error (generally I get 3-4 with WAAS lock after 5 minutes). If for some reason it's > 5ft I generally restart the averaging and reposition the antenna.

 

HV3506 is an example, so you don't have to look it up, here's the text I logged:

 

HV3506'RECOVERY NOTE BY GEOCACHING 2005 (LWB)

HV3506'NO WOODEN POST NEAR THE MARK.  CAN BE SEEN WHILE DRIVING BY ON THE

HV3506'ROAD.  HANDHELD GPS REPORTS LOCATION AS N 38 58.679 W 077 39.341

HV3506'(WGS-84).

 

It would be nice if they had a standard way to report "informational" coordinates.

That would allow them to be used by sites like geocaching.com for better placement on maps. I've found many on the wrong side of roads, I'm waiting for one on the wrong side of a creak or other element that makes getting to the actual mark much more time consuming.

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Ok, there are a few animosities here, Let me see if I can help.

 

I have covered some of this ground before but it is worth going over again.

 

Part One.

 

First WGS 84... Some people feel that WGS 84 and NAD 83 interchange. They don't. There are times when horse shoes and hand grenade theories are doable, but really, this is not one of those. The important thing is knowing when is which. There is a difference between the two Datum of about 1 meter because they both use a different mathematical model for the earth center. After all, We are helping to update a database which is the National Spatial Reference System, and it is serious minded important work. It deserves being held in our highest esteem. We should treat it with care. WGS 84 will get you there but when we work and affect changes to the NAD 83 Database, we should use NAD 83.

 

Further, if Handheld GPS units were to become more accurate, this difference would easily become revealed. The GPSr is giving you at best a 5 foot circle of accuracy, and if you are using WGS 84 you could be adding more inaccuracy. In my Professional work, have DGPS instrumentation that I can walk with in my hand that is accurate to a 1/100th of a foot while I am walking around. In other words, Pro Gear reveals this difference.

 

What I am saying is this. NAD 83 is a Datum. The North American Datum of 1983 is the official name. It was developed by the NGS. These Stations which we call benchmarks here at geocaching are part and parcel the physical references for the NAD 83 Datum. For the sake of argument, you cannot separate these monuments from NAD 83 because they are NAD 83, (and NAVD 88) so, if you use a different datum to describe where they are, you inaccurize them, because the professional is using very accurate equipment. It is easy enough to set the GPSr to NAD 83 as opposed to the WGS 84 Datum and it will convert all your waypoints to NAD 83 For you while you are toggled to that mode. Then when you want to Geocache, you can go back to WGS 84, or you could just leave it at NAD 83 as that will be close enough for a geocache.

 

Now as geocachers with consumer grade equipment, it is hard to see the accuracy, I know this too because when I am with my GPSr I find myself wanting very much to be able to see inside the 5 foot circle of accuracy. Our GPSr does not reveal it, but it is there. The NAD 83 is "Adjusted" because there are CORS Stations, Constantly Operating Reference Station, which along with other stations track the surface of the earth all the time, it is not just a snap shot, The NGS can look at any of them over time, all day every day monitoring and note changes, (read watch the earth move) and guess what? They change! Another reason why they readjust is because the see the changes and the run least squares again, Guess what? New results! Then the Geodesists don't help matters by creating new Geoid models based on Mathematics and testing, further observations of the world, and in our case, the North American Continent and each State and Counties or Cities, even Countries which participate...

 

In Summary, Gravity is found to not be stable throughout the earth's surface, and this causes minute or bigger changes to terrain. Math is becoming more inclusive of the variables, some are newfound variables as well. New theories come to light, and we can never ever just leave things alone! What fun would that be?

 

We have found things are not ever static. Adjustments never stop.

 

WGS 84 is a different Datum, Created by different geodesists at a different agency for a different purpose. It accounts for the Vertical and Horizontal all at once, yet is not super highly accurized to the millimeter like the NAD 83 Datum is on the Horizontal, nor like NAVD 88 is on the Vertical. (NAD 83 can do both Vertical and Horizontal as well but is only accurized Horizontally. Vertical Control in North America is handled by the NAVD 88 Datum.) WGS 84 is maintained by the Department of Defense and they do not adjust for small anomalies on the North American Continent, They just put a Datum out for the world and allow other countries to use it and perform their own local adjustments, A lot of Europe and Asia does this. We don't. The US Department of Commerce Heads up the NGS and they do it for here. This is not to say the Military cannot find it's way around North America, It can, but not likely to the millimeter. Tanks and Bombers do not need millimeter accuracy. Centimeters are close enough. This is also not to say that the NAD 83 Piggy backs on or is related to WGS 84 in any way. It isn't.

 

Part Two...

 

What does "Adjusted" really mean when we look at a datasheet. Well, where to start?

 

Ok, lets keep in mind that on any random sample of a group of PID's there could be both Horizontal and Vertical control involved. But I would like to recommend that we not think of them this way, because It is possible, even though I am being completely hypothetical, that PID ZZ 1234, ZZ 1235, ZZ 1236, and ZZ 1237 could be A, all Bench Marks, B, All Optical Triangulation and a mix of any order, C, all GPS derived A or B order, D, All CORS or some derivative thereof, Or E a mixture of Any of the above and you could find this to hold true in any random sample. The PID has no bearing on what kind of data the station has. It is just a form of dewey decimal system of sorts... A way to catalog it all.

 

So since we have to think of each station specifically, Lets. The Hypothetical, randomly assigned PID, ZZ 1234 just happens to be, say, a Bench Mark, and what this obviously means to most who understand the terminology, is that this data is for Vertical control. It has been carefully measured to within better than 3 inches of accuracy and is likely more accurate than one half inch, On the Vertical Only. ( I routinely level to 1/100th of a foot) But where is it? We do not think of where we are Vertically, we think of where we are Horizontally. Well, when Bench Marks are Surveyed in, in a process that was called Vertical Leveling back when it was all done optically, Uually, but not always no horizontal work was done. (Some stations got both treatments at different times, and it was usually triangulation that got both. First triangulation and leveling if a Level line happened to be passing by. I have seen leveled RM's as well...) The "where" was not established by a Survey, no angles were turned, so the where was determined by pulling out an USGS Topo or something similar (NGS Had their own inter-agency maps too) and the location was SCALED by using the Scale on a Ruler aligned to the scale on the map and so it goes... It was meant to get you close, and the narrative description would home you in from there. The basis for doing this was to simply locate the station so others could find it.

 

Enter today. The GPS era where we can know where we are with 5 foot accuracy. It is like Compact Discs that digitally reveal the flaws of the old Analog tapes used to record things in bygone eras... We commonly reveal the sad truth that scaled positions are not as accurate as we would like.

 

Here are a few fairly hard fast rules that you should be able to count on in most cases.

 

If you pull a PID from the database and see the location is "Scaled", You can pretty much bet it is a Bench Mark Station which has never been GPS'd or Triangulated optically, as so to have both types of data.

 

If the location is Adjusted, then there is Horizontal Survey Data ascribed to the station and it is highly accurate to a degree which a Consumer Grade GPS cannot reveal. I am not saying you cannot find errors. We all have. If you are looking at the station and the stamping says you have found it, you are set to NAD 83 and the GPSr Coordinate does not match an Adjusted coordinate to the degree with which it is able, you may have found an error.

 

Doing an Adjustment of Stations of Scaled and Adjusted Types together is impossible as they are totally different. The Scaled Station is Scaled for Horizontal location but the actual Data is for Vertical purposes, so the Least squares adjustment is in the vertical, not the Horizontal. Even the Datum is different. NAD 83 does not adjust for the Vertical. The Vertical realm is all NAVD 88. Conversely the Least Squares on adjusted marks is all Horizontal Survey and since the location of all vertical stations is not part of the NAD 83 Datum, they do not become part of the adjustment.

 

If there are any further questions about the come and go of all this, Please feel free to ask. It can be a confusing subject!

 

In Edit, I want to add this point. I have been reading a lot lately where people are finding the coordinates off by many feet. It is not a bad thing, and we are not finding grievous errors here. The Meaningful data on those stations is in the Vertical not the Horizontal. But we can improve it. This is just a scaled vertical control station and they will never be found as adjusted unless they were GPS'd or optically Triangulated, and almost always be off. We can make an effort to hunt vertical control and add our found NAD 83 Waypoints to the database Narrative to improve this, if it is not a GPS Station. GPS will be A or B order Vertical Control. In GPS land the Horizontal Location will be to the millimeter. Optical Horizontal Control will always be Adjusted and more accurate than a GPSr can reveal.

 

I covered a way we can format this for the narrative earlier in this thread but this should give us all a look at a way we can format the addition to the data for the narrative as a for instance:

 

WAAS CORRECTED NAD 83 GPS COORDINATES:

47 40 59.3(N) 122 23 11.7(W)

 

Remember to use NAD 83! I Hope this helps!

 

Rob

Edited by evenfall

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It is easy enough to set the GPSr to NAD 83 as opposed to the WGS 84 Datum and it will convert all your waypoints to NAD 83 For you while you are toggled to that mode.

That's easy enough, with most receivers, however, is it accurate?

 

I point to questions in the NGS FAQ: What is WGS-84? Does it change?

 

Note also the following question about conversions. In particular, the question and first answer:

 

Where can I find the transformations between versions of WGS 84 and the versions of NAD 83 and the versions of ITRF?

 

We know of no compendium which describes the transformations for all possible combinations of versions.

 

Based on this and other posts I have seen here there are multiple versions (refinements) of NAD83, and WGS-84. It appears no one has figured out how to transform between all of the combinations, which makes me wonder how the GPS unit is estimating the conversion.

 

Further, papers like this lead me to believe in the NGS's eyes there are no formulas:

 

Relation of NAD83 to WGS84

 

However, in the NAD 83 adjustment these coordinates received corrections due to interactions with other observations (mostly classical triangulation and traverses), while no such corrections were made in the determination of the WGS 84 coordinates.

 

I highly doubt my GPS is smart enough to know about classical triangulation and traverses, which the NGS seems to include in their GPSOBS conversions (which I can't find any concrete data about on the web site.).

 

As much as it makes sense to keep things in NAD83, from my not-a-trained surveyer eyes it appears the GPS units internal conversion is likely the over simplistic "off by a meter" view of things, and not adjusted in the way professional surveyers and/or the NGS would adjust satellite observations to NAD83. Thus, letting the GPS do the conversion is highly likely to introduce inaccuracies in the data.

 

I guess the basic question comes down to this: When a professional surveyer sets up a GPS rig and monitors a location for a day they receive GPS data which is in WGS 84. Does the surver or the NGS then convert it to NAD83? What forumla is used to convert to NAD83? Is there any evidence hand held GPS receivers perform the same conversion? If it doesn't, can I apply the same conversion by hand / with some other program?

 

Also, while I'm interested in the technical details (as I think all of us are facinated by these details), at the same time I think it's all a bit of a moot point for what we're talking about. I think the only thing people are submitting coordinates for are SCALED benchmarks (in the vertical control sense) to make them easier to locate. No one is trying to update adjusted coordinates. We're trying to make it so you can get within 4-5 feet of a benchmark by a handheld GPS, rather than 300' with map scaled coordinates. Even the professional surveyer using the coordinates for that purpose is more likely to put them in a street pilot in his car and say "Drive to" than to try and use them in any way with the survey grade rig. Those units all work off WGS-84 by default.

 

All that said, I still think this is an area where the NGS needs to step up. In addition to "SCALED" and "ADJUSTED", there needs to be "REALLYCLOSE" (ok, so I'm sure they can come up with a more professional name). When we find a verticle control who's scaled coordinates are way off (as some have been found MILES away from their SCALED coordinates) there should be a way to update those coordinates so radial searches and the like work properly, but also so they are not mistaken for "survey grade" in the horizontal. I think this does a service to the professional surveyers. If the coordinates are a mile off, and us geocachers can update it to be within 5 feet, now when you do a radial search you'll realize the mark is a mile futher / closer and can choose to use it as appropriate. Also, being able to walk over it with a handheld GPS is a lot quicker and easier than looking around and wondering if the 6" tree in 1942 is now the 20" tree, or if that's a different tree. If the NGS had a way to enter "REALLCLOSE" coordinates then they could establish a standard (no doubt NAD83), and also make a way for geocachers to enter WGS-84 native out of their receivers and have NGS do a highly accurate, able to be adjusted over time conversion.

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NGS works in NAD 83 and NAVD 88. If you don't mind, use that as your datum just to keep it simple. If you really really want to use WGS84, thats fine. We already know that handheld data is not that accurate, and we use it accordingly. But almost anything is better than scaled.

 

-Casey-

 

edit: I removed some information that I learned was not exactly what I thought it was. Just goes to show that you need to ask the right people the right question.

Edited by caseyb

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When a professional surveyer sets up a GPS rig and monitors a location for a day they receive GPS data which is in WGS 84. Does the surver or the NGS then convert it to NAD83?

 

Yes and the post processing software can process it to any datum you chose.

 

 

What forumla is used to convert to NAD83?

 

Its so compicated that only a computer can handle it.

 

Is there any evidence hand held GPS receivers perform the same conversion?

Yes they do.

 

If it doesn't, can I apply the same conversion by hand / with some other program?

 

Its easier to place the GPSr in the correct datum.

Edited by Z15

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To add to elcamino's list of answers, Some Cities, Counties, And Specific Projects (still) require us to Survey in NAD 27 and or do all the Vertical work in NGVD 29 even though they are both no longer officially supported. They will refuse any survey from newer datum and refuse to certify it. If that is what the local rules are, even if we think they are antiquated, it is what we use. It is a both a political and economic decision on the part of some areas, They have not the funding to properly convert, Or the powers that be are old school thinkers and refuse to move along with the progress of the world... It happens. And so we set the equipment accordingly.

 

It does highlight how important being in the correct Datum is however...

 

One thing that is nice, and a feature of any GPSr, is that there are many Datum already loaded into it, and you can easily toggle between them. If you were to make waypoints in six different Datum as you went, you would see them all in your waypoint list, but they would all display in the Datum you currently have the GPSr Set for. In other words, Automatic conversion. You don't have to go back out and re accomplish the waypoint, just change the Datum setting in your GPSr from WGS 84, or what have you, to NAD 83 and all the waypoints automatically convert. They all now are being displayed in NAD 83 if that is the setting you chose.

 

If you no longer have the Coordinates in your GPS it may be too late, but on the off chance you may need to convert some numbers back and forth between NAD 27 and NAD 83, the NGS Geodetic tool Kit Has this offering: http://www.ngs.noaa.gov/TOOLS/Nadcon/Nadcon.shtml

 

Rob

Edited by evenfall

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I did a little experiment. I set my GPS outside where it has a really good skyview and waited about 10 minutes for it to find all the satellites, get a WAAS lock, and settle down. I then took a point in WGS-84, one in NAD 83, then one in WGS-84, then one in NAD-83. All were averaged for 30 minutes, which is longer than I would probably ever wait at a benchmark. Estimated error on the unit (Garmin GPS V) was 3' after all four samples.

 

They are:

 

A) N 39 02.525 W 077 23.928 H 280 (WGS-84)

:rolleyes: N 39 02.526 W 077 23.929 H 286 (NAD 83)

C) N 39 02.526 W 077 23.929 H 300 (WGS-84)

D) N 39 02.525 W 077 23.929 H 280 (NAD 83)

 

So, within the accuracy of the handheld GPS they are identical, at least here. I wonder what the difference would be with more precise gear.

 

Anyway, ok, I'm sold, NAD83 only, not that it seems ot actually make a difference in the coordinates.

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Bicknell,

 

The observable difference is this. The consumer grade GPS units are no more accurate than 5 feet. if you are within five feet of where you need to be, the GPSr will tell you that you are on the spot.

 

The Pro Grade Gear I use in my work will survey to the Millimeter, Actually smaller than that, but the millimeter is something we can all imagine. And a millimeter is a very - very small spot. The GPSr cannot even resolve a number this small so you would never see the accuracy.

 

Now if you were to imagine Two Datums, call them NAD 83 and WGS 84 then picture a computer image of two transparent, earth sized spheres that you can see a dot for the sphere center (earth center) inside of each, and we could see the translucent surfaces. If you could walk into the computer image and were to take a tape measure and hook it to the sphere center point of the NAD 83 sphere, and pull it to the sphere center point of the WGS 84 Datum sphere you would measure a distance of one meter separation.

 

Now this is not the whole problem solved. Pretend we have a frame of reference for these two spheres which is separate from the Datum them selves that allows us to compare them. Say it is a Plane reference where we know know where level and Plumb are. we call this frame of reference the ellipsiodal height. There is a paper on this you can read here that will sort of explain in great detail some of the concept I am trying to simplify... well sort of, and the main thing is to just get the gist of the idea here, not become a geodesist unless you want to be one... Here: http://www.ngs.noaa.gov/PUBS_LIB/gislis96.html Just remember that in this explanation, we are also thinking beyond the scope of that paper... There is probably a better one too but this will work. Anyhow, When we compare these two spheres as being inside one another we find that they are not level on a horizontal plane nor Plumb on a vertical one, and so a Cartesian Coordinate way of thinking has to be applied here, because when we actually compare the datum, we do so on the surface of the Sphere.

 

So on the surface of the sphere if it were a perfect sphere there would seem to be a few, (4) places of note. Two places where we are at an extreme one meter apart, and at a right angle to those places, 2 where we should Null and both Datum would read the same coordinate. But this never happens. Why? Because WGS 84 and NAD 83 Not only use different earth center models which cause the datum shift in the first place, but they also use different versions of geoid models which further skew the result. One other thing happens. The earth is Not a perfect Sphere, it is actually ellipsoidal and the surface of it undulates and is not smooth, this is partly why they coined the term Geoid to describe the surface of the earth... Remember there is Death Valley, Mt Everest and everywhere in between...

 

It is conceivable and correct that there are places , many places on the surface of the compared spheres and the earth as well where the difference is somewhere less than a meter, and comparatively run the gamut from zero difference to the full meter, but to compare them in not just a straight line comparison. To see it we need the Cartesian thinking. This is a three dimensional set of Spheres. If from our frame of reference the WGS 84 Sphere was up and to the right of the NAD 83 sphere, then all the errors would be Up and to the right and we would then have to figure the differences between how much up on the vertical and how much to the right on the Horizontal to calc the coordinate. It is conceivable that in any given place a comparison of the Datum could be horizontally off by a foot, but in the same spot, vertically off by 2 feet yet the Hypotenuse, which is the straight line between the 2 points being compared would be less than one meter. You can observe how this works with Pythagorus' Theorem: http://www.ilovemaths.com/2pythagoras.htm

 

Most importantly here is that we know this, but we never bother to do these comparisons. We Know this happens and don't want it to, and we avoid this because we stay in the datum we need to. We don't intermix the Datums because this introduction of errors is what will happen and we don't want to compare it, we want to avoid it! This sort of skewing is a very bad thing for accuracy in our business. And this is why we stay in the Datum we are asked to. I guess I am asking you to trust in some things that you cannot see with your equipment but they are there... really!

 

Rob

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Given the excellent test above done by bicknell, the researched post by caseyb, and the GPS unit conversion note by evenfall, it appears that my previous NGS FAQ topic post has been answered.

 

Anyone want to take a hack at this result?:

 

---------------------------------------

Q. I found a mark and its horizontal coordinates are listed as SCALED. I have the coordinates from my GPS for this mark.

What format should I use to report the coordinates to the NGS?

What Datum should I be using in my GPS unit?

 

A. Although the Geocaching site uses the DDD MM.MMM format, here at the NGS we prefer that you use the DDD MM SS.S format.

Example:

Handheld GPS coordinates were N 39 45 56.1 W 077 38 27.2

 

You can set your GPS unit to any datum you wish while getting the data.

When entering your mark recovery report, you should have your GPS set to either NAD 83 or WGS 84 datum. Although NAD 83 and WGS 84 are closer together than the accuracy of your GPS unit, you might prefer choosing to set your GPS to NAD 83, the NGS datasheet standard.

---------------------------------------

 

This forum software removes extra spaces, but in the Example above, I put 2 spaces in between "were N" and 2 spaces in between "56.1 W".

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Note that my rather elderly GPS, a Magellan 310, does not have a NAD 83 datum. I suppose I could record the data in UTM and convert to NAD 83.

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Simple solution IMO.

 

Set the GPSr to NAD83 and you are set for life.

 

Like the saying; "When in Rome, do as the Romans do."

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Simple solution IMO.

 

Set the GPSr to NAD83 and you are set for life.

 

Like the saying; "When in Rome, do as the Romans do."

I keep my ancient but very servicable Trimble ScoutMaster set to NAD83 and DMS for Bench Marks. It has an automatic average function and lots of memories that work well for this purpose. My geocaching GPSr is set up for finding the objects in the first place and I don't have to try to keep uploaded memories seperate from the on site waypoints. Seems to work well for me.

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Z15 Posted on Mar 17 2005, 04:54 AM

Set the GPSr to NAD83 and you are set for life.

I must agree with this. I see the benchmark pages now say NAD 83 (I believe they used to say WGS 84, but I can't remember for sure. The geocache pages don't give any datum.) Anyway, it does seem silly to even refer to WGS 84, even if it doesn't make much difference. If yer goin' benchmark huntin' use NAD 83!

 

---------------------------------------

Q. I found a mark and its horizontal coordinates are listed as SCALED. I have the coordinates from my GPS for this mark.

What format should I use to report the coordinates to the NGS?

What Datum should I be using in my GPS unit?

 

A. Although the Geocaching site uses the DDD MM.MMM format, here at the NGS we prefer that you use the DDD MM SS.S format.

Example:

Handheld GPS coordinates were N 39 45 56.1 W 077 38 27.2

 

Set your GPS unit to NAD 83 format, the NGS standard.

Tip: when you do your NGS mark recovery reports, also set your GPS to DDD MM SS.S format.

---------------------------------------

 

At this point, I'd like to lobby for getting Groundspeak to change their benchmark pages to use DDD MM SS.S format !

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Blackdog,

 

I like the way you are thinking. Like I have said in more than one previous post. Since these Monuments are part of the very basis of the NAD 83 Datum, Uh, Why would we want to use any other Datum? Since NGS Style Benchmark Hunting is basically about Very High Technical Accuracy, It Goes without saying.

 

It also goes without saying that even though Geocaches are in the WGS 84 Datum, NAD 83 is close enough to use to hunt a Geocache, Because the Technical accuracy doesn't really matter.

 

Geocaching.com likely realized something early on and was simply trying to keep things simple. Fresh out of the Box, a GPSr is defaulted to the WGS 84 Datum and the display is set to Decimal Minute Format. I would imagine they did not want people to have to become more technical than necessary in order to geocache so they set the game up around those parameters. After all technical things are not fun for most people, just some of us seem to enjoy this. Later entered Benchmark hunting, the same theories were applied to the database, and then we as benchmark hunters evolved.

 

Now we have come to understand that this case of trying to keep it simple is not always in our best interest, and could be made worse if GPSr manufacturers ever allow us to have more accuracy than we currently have in our handhelds.

 

I concur, Set to NAD 83 and forget it. It is good enough to Geocache with and best for the serious benchmark hunter. Lobbying Geocaching to alter the format back to degrees minutes and seconds is well worth consideration but I wouldn't expect to see them change it. It may be a choice of accuracy over simplicity for us, however those who want to benchmark hunt seriously can easily make the necessary changes. The folks who just want to play may see it as too much bother and not enough fun.

 

For those who may want to know more about the display format interaction, here is the formulaic method for converting display formats (longhand method): http://life.csu.edu.au/geo/dms.html

 

Rob

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I concur, Set to NAD 83 and forget it. It is good enough to Geocache with and best for the serious benchmark hunter. Lobbying Geocaching to alter the format back to degrees minutes and seconds is well worth consideration but I wouldn't expect to see them change it. It may be a choice of accuracy over simplicity for us, however those who want to benchmark hunt seriously can easily make the necessary changes. The folks who just want to play may see it as too much bother and not enough fun.

In the "let the computer do the work" it seems to me that the coordinate display format should be a user preference item, and that the input field should default to the same format but have a pull down for other formats as well. The default can stay the same, but people doing more benchmarks can set it to the NGS preferred format.

 

Indeed, geocaching.com already gets this half right, you can pick DD MM SS.SS,

DD MM.MMM, or DD.DDDDDD when entering a waypoint in a log entry. If they just had a way for an individual to change the default, and have that also affect the display, that would do the trick.

 

As for the NGS, they obviously have a rigid output standard. There's also no "input box" for the type of logging we're doing. I still feel they need an "add a waypoint" capability for SCALED marks only, which would have an input box, should have selectable formats like the geocaching.com site, and once entered would be used rather than the scaled coordinates for radial searches, map placement, and soforth. They would not be used for survey, obviously, but that way you'd be able to search on the more accurate coordinates rather than reading descriptions to get them.

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Reading the description is very important. It is also important to remember that the NGS is dealing with the desire to keep things as accurate as possible, and to improve on that as possible. They have very rigid, rigorous standards and for a very good reason. They have to with the kind of accuracy they have achieved.

 

They allow us to submit information to be added to the narrative section on a datasheet and a pair of eyes does look at our submission before it becomes a permanent part of the datasheet. Adding the waypoint will suffice, and perhaps the NGS may choose to change the scaled info to the waypoint, but I doubt it...

 

It is way safer to leave the scaled waypoint, and allow you to update that with a waypoint in the narrative. This way the back up data remains intact and on the datasheet. It is a form of a paper trail of events, and we have all learned that knowing any given station's individual history is important. All the Data may dovetail with other data we are not privy to as well. We have to leave all the clues in tact! :-)

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You mentioned most of the erred marks were set in 1974. I think that's your answer! Was anyone paying attention in 1974? After all, if you can remember the 70's, you weren't there. :)

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The DD MM SS.S format is great to work with, except that it has the poorest precision of the 3 formats available on most handheld units. DD MM.MMM is in the middle and DD.DDDDD has the smallest increment.

 

All are better than the usual measurement accuracy, so it isn't a big deal, but if I'm trying to refine my measurements by averaging readings taken on multiple days then I use DD.DDDDD, manually average them, and then convert the average to whatever format I want to report. I don't want any more roundoff error than necessary.

 

The measurement errors aren't random enough over a period of minutes so that averaging in the unit gets that kind of accuracy, but I'm hoping that the errors of a bunch of short term averages taken on different days will be uncorrelated so that I could get into the region where it matters. I've used this technique a couple times and have one mark that I don't get to very often that I'm still trying to improve my measurement on. I'd like to get to SS.SS with it.

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Expanding a bit upon Bill93's excellent points -

 

An investigation on formats:

 

The Conversions

 

My GPS unit has 3 options for displaying its internal coordinate measurements:

(the first column is an abbreviation)

DD decimal degrees DDD.DDDDD

DM decimal minutes DDD MM.MMM

DS decimal seconds DDD MM SS.S

 

To relate these from the smallest one (kinda like the old British monetary system - how many pence in a shilling and how many shillings in a pound  ):

The smallest is DD.

DS = (2 and 7/9) DD =~ 2.8 DD

DM = (1 and 2/3) DD =~ 1.7 DD

 

Getting Distances from the GPS

 

How long is a 1/10 of a second in feet, etc.? The East-West length changes with changing latitude of course, so I used a place near me, which is vaguely in the N-S middle of the contiguous U.S.

Instead of trying to do the calculations myself, I fiddled with the GPS unit (Garmin III+) to get them.

 

(I noticed that, when using the DD format, I couldn't enter just any values into the GPS unit - it would change my entry by 0.00001 degree sometimes. I figure that some amount a bit smaller than that is related to the unit's internal precision level or the precision of its conversion programming or both.)

 

I made 2 waypoints and referenced them to each other in the GPS so that I could read how far apart the GPS thought they were. First, I would zero-out the distance between the 2 waypoints. This wasn't always easy because of the parenthetical note above. Sometimes I'd have to resort to zeroing out the distance (fortunately the GPS let me edit this value) and then go with the pair of coordinates that would show zero distance between the 2 waypoints.

 

To get a more precise measurement of distances, instead of changing lowest decimal, I changed the next-to-lowest decimal instead, and divided the resulting distance by 10. I realize this probably isn't mathematically exact, but probably better than just changing the lowest decimal place.

 

Also, I both added and subtracted my changes and averaged the results, i.e. the distance between 36.78173 to 36.78183 and the distance between 36.78173 and 36.78163.

 

The Distances

 

DDD.DDDDD format:

Distance, changing the N value: (37+35)/20 =~ 4 feet

Distance, changing the W value: (27+29)/20 =~ 3 feet

 

DDD MM.MMM format:

Distance, changing the N value: (60+61)/20 =~ 6 feet

Distance, changing the W value: (47+46)/20 =~ 5 feet

 

DDD MM SS.S format:

Distance, changing the N value: (102+101)/20 =~ 10 feet

Distance, changing the W value: (80+77)/20 =~ 8 feet

 

The precision vs. accuracy

 

My GPS unit (no WAAS) with some averaging has about a 12-15 foot accuracy. (One can spend endless hours researching test data, relationships of error distance vs. confidence intervals, product specifications, etc., but I cut it short. :D A good site to read on this kind of topic is here.) Unfortunately, the DDD MM SS.S precision level is about the same level as the unit's accuracy so it really cuts the accuracy of a pair of recorded coordinates down a lot. The unit must pick one or another 9-foot rectangle that the position is within, thereby adding up to 4.5 feet of error.

 

The question remains

 

A review of the current topic indicates people favoring DDD MM SS.S format. The NGS uses DDD MM SS.SSSSS for adjusted marks and DDD MM SS for scaled marks, so it seems rather obvious to use the DDD MM SS.S format choice that amateur grade GPS receivers have (unless some have DDD MM SS.SS - does yours?). As we have seen, this obvious answer isn't the most precise. If I report coordinates, I like to see how it compares with the scaled coordinates. That comparison is difficult if you don't use DDD MM SS.S format, but is this comparison really important to be able to do? The question remains - what format should we be using when entering coordinates to the NGS?

 

A recommendation

 

Go ahead with the DDD MM SS.S format. It's a 9 foot fuzzball, chosen by a GPS unit that 'sees' a 5 or 15 foot fuzzball depending on whether you have WAAS or not, but the end result is a whole lot better than the (+- 6 seconds) 600 foot fuzzball of a scaled position!

Edited by Black Dog Trackers

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Blackdog,

 

I think I have tried to answer your question on more than one occasion, but I will try to do so again.

 

You Asked: "The question remains - what format should we be using when entering coordinates to the NGS?"

 

This Question does not really remain, as it really doesn't need to be a question, and hopefully I can explain why.

 

The NGS is a subdivision Department of the Department of Commerce. They control all the Civil Geodetic Data in the United States and set the standard for all of North America, Including the countries of Canada, Mexico, and has also been extended to the Caribbean. They are the Creators and Owners of the NAD 83 and NAVD 88 Datums, and continue to further the science of geodesy with the best people they can find, working on new methods all the time. This is their Standard and it is up to the users of their standard to follow it if they use it. When we use a system, we accept that we also use that systems set of Standards and Practices. Many, Many Books are written about Standards and Practices, By the Feds, Each and every state, Many Municipalities... And we as Surveyors, (and anyone else) have to follow them. It is just the way the game is played.

 

When a Practice seems to be in place as a standard, yet does not seem to be expressly permitted, advocated, or forbidden, it is good form to follow the practice or someone will be along to write a rule governing the Practice in question shortly. It is kinda like Murphy's law in that respect. The correlation to the Law is always something that will make things more painful to use, I assure you! That is just the nature of this sort of thing. :-)

 

They (NGS) set a Standard and the hope is that all People, Agencies, Municipalities, what have you, will enjoy the high accuracy, and so to make this a repeatable experience, we all adhere to the methods set forth. Many of these standards are historical and Age-Old.

 

D.M.S is a format that has been used for most all Surveying all the way back to the early days of this countries history, likely much of the history of Survey. Perhaps the practices of the Sumerians, and of course we see the higher accuracy of this format by the number of places the number is carried to the right of the decimal. It is designed around the way a Transit, Theodolite or in today's world a Total Station divides up a 360 degree circle. We don't see if we can introduce errors to it by using different methods, we use the one that makes most sense, as all the old instrument divided a circle in this way, and the Math was done with a paper and pencil. It was not good practice nor exactly easy or timely to play with alternative conventions until quite recently. In fact it was not long ago that if you were on a survey crew and suggested this, or an idea as such, the party chief and some of the others would likely look over the top of their glasses at the mention of your idea, and it could be a couple weeks before they talk to you much, or again. Yup, It was Old School, and in some places and ways, it hasn't changed much.

 

All the Data is output in the format they have always used, and it stands to reason that it should continued. These numbers are not about how close they are with a $350 GPSr, they are about how close they are with a $10,000 RTK GPS. At best in any format, a GPSr can give a circle of 5 foot accuracy. Remember, all we are trying to do is physically find the Vertical control and improve it's scaled location with a GPSr. If we want this improvement to have credibility, we need to adhere to the standards being used.

 

There is a bigger danger for error being introduced by using the alternative formats that we might think, and though it appears we think we can test this, but it really is more of a happenstance.

 

As an example, Recently, I think I read where there was some confusion over inputing data to the mark recovery page at the NGS site... Somebody used the back button but forgot to correct all the fields for entry to the proper *new* PID for submittal and so they wound up writing Deb to correct this human error. I think it is very cool that we all try to be this conscientious and get our errors repaired. I am sure it has occurred to more than one regular here at the Forums. But this human factor is the purpose of my point.

 

In the same Fashion, this is why I would like to encourage everyone to just accept the practice of using the NGS standard for D.M.S format when dealing with updates to the datasheet. We may think there is little difference in accuracy, but the crippling factor is when mistakes get made, You know, the Human errors, and they will get made. The Three formats all output a different number. When matched to the correct output format each describes the same place. But, and a Big But, if we mix our metaphors, or output formats with our data we can quickly inaccurize the result by mistakenly calling a D.MM number a D.M.S number, and I have seen this happen more than once in my career. This mistake will foul the actual location value up by Hundreds of feet, and all by a very innocent mistake.

 

I have personally, and professionally hunted D.MM waypoints in D.M.S and they are not findable by that method. My mistake was not realizing that the person before me had not followed the standard practice, and when I changed formats I walked right to it. The important thing to note is that I should not have had to worry about such practices if the person before me had followed the standard. Things that make you go Hmmmm are well, not always a good thing... Just like Arsenio Hall and Martha Stewart on a date, if you could imagine... Uh, well, or don't :-) We don't want to go there...

 

What I said is if we submit a Number output in D.MM and mistakenly call it D.M.S Number, or visa-versa, or juxtaposition by mistake, the result will now be inaccurate by hundreds of feet. This is not good, and not only can it happen, it does, happen by just adding a D.MM number to a datasheet without saying which format you used.

 

** All Professional users of the NGS Datasheet will be assuming the D.M.S Format and field conversions are not what they want to have to do to make it work for them. **

 

That reason alone is the best reason to stick with the D.M.S Format if there are no others.

 

Soon we find our selves asking did I do that right? as we were back and forth between so many formats...

 

I realize that not all GPSr units over time have not been created equal, and we all have the one we have. Good bad or indifferent, it is always considered a good practice, or good form if you will, to stick with the formats being used, or as someone recently pointed out, When in Rome. If we always stick to the standard practices and always do it the same way, we get into good habits which never have us wondering what we did or if others will be able to figure out our work. This is also why we surveyors can figure out the work of other Surveyors. We stick to the practices which are the accepted norms so others can duplicate our results.

 

We can of course choose instead to be independent and do it our way, but we might not be seen as helpful by everyone concerned if we do.

 

It is cool and informational to know, concerning the ways the GPSr seems to handle this information in the different formats, and it may be cool to write the manufacturer and see how they test all this as they develop their own Specs, for each brand and type of unit. If they are using a Parts Per Million method of determining accuracy, it is likely that the accuracy is the same in all formats, yet changed by the way the format may truncate the data output to the screen.

 

I hope this helps you understand, but if you like, you can write Casey, Dave, or the NGS and see how they come down on this. I perceive that all their datasheet output formats already tell the tail. In any case you are correct, this new position is usually better than a scaled position any day!

 

Rob

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evenfall -

 

So your point is that we should be using DDD MM SS.S even though this will force us to be less precise than the measurement accuracy of our GPS units, because using a format that professional surveyors expect is the more important than the accuracy difference.

 

I agree as well - perhaps you missed seeing my Recommendation in my last post.

 

Anyone have a differing point of view on this?

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Black Dog,

 

In My professional opinion Yes. The difference in accuracy between these modes on a GPSr is not going to matter to the surveyors as much as keeping with the conventional way they think. We as geocachers are simply trying to improve the position of a scaled location. With the equipment a geocacher has that is all you can do. I as a Surveyor use this Data on the clock to do my work in a timely, accurate manner. My equipment is capable of infinitesimal accuracy in any display mode. If I can stake a 2:1 slope ratio with a vertical soldier pile wall cut 40 feet above what will be finished building pad grade, all while keeping track of my topo for earth moving quantities as per job bid item, I can sort out the last 5-10 feet of an improvement to a scaled location.

 

The Culture of Survey Data Annotation is in D.M.S Format and we are not going to change that 200+ year culture. We should make all data entries in the Format which is expected. If we do not, we will cause Surveyors to make errors or waste time if they do not catch what method we did.

 

I can tell you first hand that looking for a Location in the wrong format can lead to errors of over tens to hundreds of feet.

 

Let us avoid causing errors by not using formats that end users of the data will not expect.

 

No one is going to change this convention. The consumer grade GPSr is not dual channel nor often DGPS capable. This sort of accuracy simply is not enough of a big deal to matter to the consumer level, as we are talking about improving a scaled location to within 10 feet. I am sure 10 feet is a lot better than hundreds eh? In that respect we have already done the Surveyor a huge favor, given them a big leg up on the hunt. That is worthwhile and good to smile about. I can tell you that I for one am grateful for the improvement of the To Find. So let us accept that this is the best we can do with our consumer grade gear.

 

Please remember, we Surveyors are not going to perform Horizontal Surveys from a Bench Mark. This is simply to aid the To Find accuracy and that is all. These are Vertical control Stations. When I am looking, and if I am looking with GPS I am looking in D.M.S Mode... Always.

 

We are not going to change the way Surveyors and Engineers think and it is not helpful to add one more thing for them to remember. I am one of these people and I know my brethren well. If they read your D.MM entry and follow their training and conventions of working in the D.M.S formats as they are required to do by every municipality or other agency around , this little conversion will throw them off by hundreds of feet if they overlook it, and they will overlook it. When we do this to the Data, we are asking them to convert for you, the Geocacher, when in reality, we should be doing the conversion for them. They are the prime end users of the NGS Data. The Surveyors are the Customers and Clients of the NGS and that is the Customer service they provide the users of their database...

 

I did not miss your recommendation, but more importantly you left the premise of what you felt was an unanswered Question, and I very much wanted you to have the answer to that Question. I also had a sense from how you prefaced things that you felt your unanswered question held higher importance than the recommendation you made. We surveyors do not really want to see 40 different ways of convening on the where of a Bench Mark, we want the one we have been using for 200 years... When the Surveyors try to answer these questions for you here in the forum as you pose them, Please trust our experience. We don't know everything but we are doing our best to give you the best information we have.

 

Thanks, Rob

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you left the premise of what you felt was an unanswered Question, and I very much wanted you to have the answer to that Question. I also had a sense from how you prefaced things that you felt your unanswered question held higher importance than the recommendation you made.

 

Yes that is true. What I have found to be rather odd, from when I first visited it, is that the NGS mark recovery site is, in my opinion, missing some important instructions, definitions, and specifications. Like fairly precise definitions of "good", "poor", how often to report, etc. Therefore, I like caseyb's idea of having an NGS reporting FAQ topic. In my opinion, such an FAQ should really be on the NGS site with a link from the Mark Recovery page.

 

Until the NGS does this, the question is officially open, it seems to me. I think the NGS should make the question not open. Perhaps they're considering that and watching this, I don't know.

 

It won't be you or me that decides. It must be the NGS who decides, and I, at least, think that they should give the answer on their website. No matter how much you and I and others think it should be DDD MM SS.S, other people will use other formats until the NGS puts the instruction on their website or a new version of their mark recovery page.

 

One can say that the NGS' use of DDD MM SS.SSSSS on adjusted marks and DDD MM SS on scaled marks really implies that we should be using DDD MM SS.S but until the NGS website says that's what we should be using, it unfortunately remains an opinion.

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