Jump to content

Reporting G P S Coordinates To N G S


PFF

Recommended Posts

Hi, Group:

 

I'm wondering if there is value in including coordinates from a consumer-grade GPS receiver when writing recovery notes for the NGS database?

 

My unit's resolution is Degrees, Minutes, and Seconds to one decimal point. This hardly compares with Adjusted Coordinates which go to six or seven decimal points. On the other hand, my readings are considerably more accurate than most Scaled Coordinates. (We're speaking only of horizontal positions, here!)

 

Related question:

If including the coordinates is of value, is it worthwhile to state the displayed accuracy? At the tenth of a second level, does anyone care if the reading is plus/minus 15 feet or 7 feet?

 

I generally include my readings in the GEOCACHING recovery notes. But I'd like the professional surveyors to weigh in about whether they care to see this in the NGS data sheets.

 

Thanks,

Paul

Link to comment

Our consumer-grade GPS receiver coordinates are an aspect of the to-reach information for SCALED marks. If any professional surveyor is using a handheld GPS unit to find a SCALED mark, our coordinates will help find the mark.

 

I'm assuming that you're not talking about submitting coordinates for ADJUSTED marks, which would be a waste of everyone's time.

 

BTW I am not connected to the surveying profession.

Edited by Black Dog Trackers
Link to comment

Paul

 

Yes, Depending on the Type of Survey marker, there is added value in submitting this information.

 

If you Find Vertical Control, and it is a Scaled Location then by all means, Please feel free to submit your GPSr derived location for this station if you find it as it will almost surely improve it. The type of markers that will usually be improved with this sort of information, are Bench Marks. Please refer to the NGS Datasheet to confirm what is needed.

 

On any type of horizontal positioning that is not scaled positioning, you are not going to be able to improve the position with GPSr. There would be little if any value in reporting the GPSr position for these.

 

Good Luck,

 

Rob

Link to comment

Black Dog; Evenfall:

 

Thanks to both of you for the prompt replies! What you say makes sense.

 

I believe the rule of thumb for me will be to report my GPS reading when it differs significantly from what is in NGS.

 

Sometimes, the scaled location is exactly on. And occasionally the Adjusted location is off--which I attribute to a typo when entering the original data into the system.

 

Of course, nothing beats an accurate, up-to-date description for dealing with the final 100 feet.

 

-Paul-

 

"Ice Plant? Honey, there ain't been no ice plant here for forty years!"

----Resident of Warsaw, North Carolina (June 1, 2005)

Link to comment

Few if any will have a measurement or calculation error large enough to measure with a handheld, but I know of one ADJUSTED mark where something has been entered wrong.

 

MH0702 was probably entered with the description of the station set and the coordinates of the next point in the traverse. I have no way to determine which elevation was used.

 

[deleted ref to some SCALED marks] not pertinent here].

 

I submitted these to Cheryl some months ago, but have seen no update. I don't know if that's because it takes a long time in the researcher's queue, or they got lost in the computer crashes at NGS, or if I should have submitted them to Deb.

Edited by Bill93
Link to comment

Paul,

 

Let me clear a few things up here for those who may not be following what we are discussing. It seems at this point a good time for me to get the right semantics out in the open and have all of us understand this as universally as possible. It has been some time since we addressed this.

 

You said, "Sometimes the scaled location is exactly on. And occasionally the Adjusted location is off--which I attribute to a typo when entering the original data into the system."

 

The scaled location is exactly on, means they got lucky. No Biggie.

 

And occasionally the Adjusted location is off--which I attribute to a typo when entering the original data into the system. I would have heavy reservations to call a location a typo. With GPSr as benchmark hunters, we have no instrument accurate enough to make a real determination here. In fact there are many things that would cause me to way sooner question the accuracy of a GPSr than a datasheet. Here is why I feel this.

 

First, read this link as a refresher for what accuracy means to these Stations:

 

http://www.ngs.noaa.gov/cgi-bin/ds_lookup....em=HORZ%20ORDER

 

Now keep this in Mind; For the establishment of the level of accuracy a station may possess, Lets look at what it took. Third Order Accuracy is a minimum of 4 optical surveys of the position for positioning and a Least Squares Adjustment. Second Order Accuracy is a Minimum of 8 Optical observations of the position and a Least Squares Adjustment. First Order Accuracy was a minimum of 12 and usually 16 optical observations of the position and a least Squares Adjustment. A and B Orders of Accuracy are GPS or VLBI Derived.

 

Now If I was looking at the position, while staring at the station, and I was set to NAD83, D.M.S Mode on my GPSr and it was radically different than the latest version of the NGS datasheet, I would re observe this location again on another day. Maybe it is an anomaly we will see in our gear or the with the satellites. If after a few hard looks I would write NGS and ask if there is something I am doing wrong. Then they will look at their Data and see if in the records they created a typo. A typo would indeed make them wrong of course but to be sure, their adjusted positions are a country mile more accurate than a GPSr can discern.

 

For Leveling, which is vertical control and in a pure sense of reference called a Bench Mark you have more than one observation creating the Data and the more observations per location the higher the accuracy after the least squared is taken.

 

Here is a good link to what "Adjusted" means as far as the NGS is concerned:

http://www.ngs.noaa.gov/cgi-bin/ds_lookup.prl?Item=ADJUSTED

 

Here is a good link to what "Scaled means as far as the NGS is concerned.

http://www.ngs.noaa.gov/cgi-bin/ds_lookup....em=SCALED%20%20

 

I would like to make this as clear as I can. Horizontal positions When it says adjusted are heavily Surveyed positions. You can trust this is as good as it is needed to be and there really is nothing we as Benchmark hunters can do to improve this position.

 

Here is where we come in. Older Bench Marks, or Vertical control is often not horizontally positioned at all. Leveling is about elevation, not location. We should look at the Fresh NGS Datasheet and look at this section of it:

 

SY0301 *CURRENT SURVEY CONTROL

SY0301 ___________________________________________________________________

SY0301* NAD 83(1986)- 47 38 53. (N) 122 22 52. (W) SCALED

SY0301* NAVD 88 - 8.690 (meters) 28.51 (feet) ADJUSTED

SY0301 ___________________________________________________________________

SY0301 GEOID HEIGHT- -23.68 (meters) GEOID03

SY0301 DYNAMIC HT - 8.691 (meters) 28.51 (feet) COMP

SY0301 MODELED GRAV- 980,725.5 (mgal) NAVD 88

SY0301

SY0301 VERT ORDER - FIRST CLASS I

SY0301

SY0301.The horizontal coordinates were scaled from a topographic map and have

SY0301.an estimated accuracy of +/- 6 seconds.

 

When we see that the NAD83 position has been Scaled, there is a chance we can help it become more accurate by reporting the GPSr position we get when we find it to the NGS.

 

If instead we see this in the datasheet:

 

SY4786 *CURRENT SURVEY CONTROL

SY4786 ___________________________________________________________________

SY4786* NAD 83(1991)- 47 40 39.13954(N) 122 23 47.77352(W) ADJUSTED

SY4786* NAVD 88 - 59. (meters) 194. (feet) SCALED

SY4786 ___________________________________________________________________

SY4786 LAPLACE CORR- -2.98 (seconds) DEFLEC99

SY4786 GEOID HEIGHT- -23.64 (meters) GEOID03

SY4786

SY4786 HORZ ORDER - SECOND

SY4786

SY4786.The horizontal coordinates were established by classical geodetic methods

SY4786.and adjusted by the National Geodetic Survey in December 1991.

SY4786

SY4786.The orthometric height was scaled from a topographic map.

 

We can see that The NAD83 Position is heavily Surveyed. In fact, at second order we can know at least 8 times. Then it was Adjusted by Least Squares Adjustment. This is a station we cannot do anything with to improve with a GPSr.

 

This Adjusted does not mean from NAD27 to NAD83. That was mathematically done but it was not an adjustment, it was a conversion, or sometimes referred to as a transformation.

 

One line on the datasheet I like to look for at a glance is this one:

 

SY4786 HORZ ORDER - SECOND

SY0301 VERT ORDER - FIRST CLASS I

 

I can see immediately whether I am working Horizontal control or Vertical control, or a Station which has both, and I can also tell immediately how good the control is:

 

AF9780 HORZ ORDER - B

AF9780 VERT ORDER - FIRST CLASS II

AF9780 ELLP ORDER - THIRD CLASS II

 

Here on AF9780, I can see it has both types of control, It also has Ellipsoidal accuracy as well and It would not have if it were not a GPS Derived location.

 

Hopefully we can look at this as something different than Scaled or adjusted. I hope I have shown that each plane, both the Horizontal and Vertical can be referred to as either Adjusted or scaled and that we can be more concise by referring to it first as Horizontal or vertical control first, then as Scaled or Adjusted afterwards. We first need to refer to it as what it is. If there is vertical data We will see it as VERT ORDER right away and if there is no HORZ ORDER then we can know that the Horizontal location is likely Scaled and we may be able to help improve that.

 

Hope that helps,

 

Rob

Link to comment

From my knowledge of adjustment procedures, if there's a typo or some other error large enough for a handheld GPS receiver to notice something's wrong, the adjustment would flag the mark as incorrect and it would not be adjusted and accepted into the NGS database until it is fixed.

 

So, I think it's not possible for any adjusted mark to be off unless it is switched with another PID's accurate coordinates, and in that case the coordinates would not really be off, they'd be misidentified with the wrong PID.

 

PFF, so in that kind of case, it would be good to sent a note to the NGS when this happens, but as evenfall says, you'd better be really really sure :D. If you ever do find one, I'd suggest emailing cheryl about it instead of just logging it with the coordinates you saw.

 

If a SCALED mark happens to be within a few feet according to your GPS, I'd recommend submitting your coordinates anyway. This is actually not non-information. It would be saying that the listed (scaled) coordinates are as good as handheld GPS coordinates. That fact would not be known to subsequent searchers if you omit submitting your GPS coordinates.

 

In conclusion, I'd suggest sticking with:

SCALED - always report your GPS coordinates

ADJUSTED - never report your GPS coordinates (unless you happen to find a 1 in 10,000 PID-switch situation)

Edited by Black Dog Trackers
Link to comment

BDT,

 

Nice addition, but please allow me retouch just a tad:

 

From:

 

"In conclusion, I'd suggest sticking with:

SCALED - always report your GPS coordinates

ADJUSTED - never report your GPS coordinates (unless you happen to find a 1 in 10,000 PID-switch situation) "

 

To:

 

In conclusion, I'd suggest sticking with:

Horizontally SCALED - always report your GPS coordinates

Horizontally ADJUSTED - never report your GPS coordinates (unless you happen to find a 1 in 10,000 PID-switch situation)

 

Vertical positioning is not something we can effectively determine as Mark hunters so thought it is good to understand, No worries there.

 

I just want to clarify this vague reference for those who may wonder or may have never encountered this prior to now. We know what we mean but it is important for those wondering, as I have a sense that some have not always had their mind around this.

Link to comment
In conclusion, I'd suggest sticking with:

Horizontally SCALED - always report your GPS coordinates

Horizontally ADJUSTED - never report your GPS coordinates (unless you happen to find a 1 in 10,000 PID-switch situation)

 

Thanks, Guys! Now, on to the next question......

 

What wording best describes the coordinates I'm entering at the NGS site?

 

Brief version: Simply give the numbers?

 

Medium version: Give numbers and indicate it was a handheld GPS unit?

 

Lengthy version: Give coordinates, indicate it is from a consumer-grade GPS receiver, and note the displayed plus/minus figure in feet?

 

Up till now, I've leaned toward #2 and #3. I didn't want #1 to imply that I visited the site with precision measuring equipment.

 

-Paul-

Link to comment
What wording best describes the coordinates I'm entering at the NGS site?

 

Brief version: Simply give the numbers?

 

Medium version: Give numbers and indicate it was a handheld GPS unit?

 

Lengthy version: Give coordinates, indicate it is from a consumer-grade GPS receiver, and note the displayed plus/minus figure in feet?

Paul,

 

I use approximately this format:

 

Handheld GPS coordintes - N36 39 24.4, W077 24 14.9

 

I used to add the model of my unit (Garmin etrex), but usually not anymore.

 

I think any professional probably has a pretty good idea of the accuracy of those units (+/- a few meters, typically, or a little more), I have presumed that adding the displayed radius of uncertainly was not really necessary.

 

-ArtMan-

Link to comment
Up till now, I've leaned toward #2 and #3. I didn't want #1 to imply that I visited the site with precision measuring equipment.

No one doing survey work is going to use any number in the description field for anything other than finding the mark. I don't think there's any danger something in the description will be mistaken for a "survey grade" mark.

 

I put in "Handheld GPS", mainly because I figure that plus the date will allow people in the future to estimate the accuracy. It's not hard to imagine that 10-15 years from now we'll have handhelds that will give us 1cm accuracy.

 

It's all rather moot though, as the whole purpose is to allow someone to drop a waypoint in a handheld GPS and walk right to the spot, and for 99.99% of the marks if you're within 6-10 feet you can see it, if you look hard enough. <_<

Link to comment

As a vague measure of local PID interest, I used a spreadsheet I had of 1,968 PIDs, with their last AGENCY reporting and its date. I downloaded the NGS approved agency list, imported it into the spreadsheet with vlookup, recategorized it to a few generalized types and made a pivot table of the results.

I'm just showing the dates starting with 1990 but the Grand Total includes all dates.

 

COMM= a commercial surveying company.

 

 Date    COMM   COUNTY FEDERAL  GEOCAC  INDIV   STATE   USPSQD  Total
 1990        37              22                       1              60
 1991         9                                       5              14
 1992        63              85                                     148
 1993         1               2                               2       5
 1994         4               1                                       5
 1995         1                                              73      74
 1996                                                        38      38
 1997         1               6                              17      24
 1998         1               6                                       7
 1999         1               6                       1       1       9
 2000         7              25                       2      49      83
 2001         9              10                       1              20
 2002        19       1       3      26      56              27     132
 2003        40               1      86       2               6     135
 2004        16              10      37       1               1      65
 2005         1               1      23                       6      31

Grand To     273     122    1079     172      59      40     223    1968

Link to comment

Evenfall—

 

We’re very grateful for the time and care you took with that explanation. We hope to inquire a little more deeply into a couple of aspects of the matter of precision and accuracy—which as you know are not the same thing.

 

Our understanding is that if a set of horizontal coordinates is ADJUSTED, then pro gear can be set up on that point with accuracy to a couple of millimeters.

 

But what was the set of coordinates on which the adjustment was based?

 

For example. PID# LW4228, Hummock 1887, on the south shore of Nantucket Island, now has ADJUSTED coordinates, to wit: NAD 83(1996)- 41 15 10.59846(N) 070 09 59.43193(W).

 

What was the basis for this set of coordinates? There are four “Reference Objects” listed on the datasheet: LW 4211, LW 4224, LW 4220, and LW 4235. LW4224 and LW4235 now report as destroyed. LW4211 has not been seen since 1894. LW4220 (which incidentally is about 610 feet N7.4W of LW4204, which was recovered in 2003), was first observed in 1887, and not searched for in 1955, and that’s it. So any azimuth reading from LW4228 to any of those four points is going to be at least 111 years old?

 

In this particular case, the ADJUSTED coordinates are for a point that beach erosion has placed some 500 feet offshore, so the chances of a successful recovery are quite literally dampened. But our question is still there: what was the likely basis upon which the NGS arrived at the ADJUSTED coordinates for this station?

 

Thanks again for your expertise and clarity.

Link to comment

evenfall - I included them in the COMM(ercial) category.

 

PFF - yep, that seems to have happened around here.

 

BuckBrooke - we can blame ArtMan and seventhings for that! :)

 

A better analysis would be to include all reports, not just the last report, but I didn't import those fields for my spreadsheet for hunting benchmarks. The last report by GEOCAC partly supplants what I was really looking for - the number of surveying profession's reports which I collected together and called COMM. The idea was to see how much they were paying attention to survey marks by counting their reports. As we all realize, they use them much more often than they offer recovery reports to the NGS.

Link to comment
The idea was to see how much they were paying attention to survey marks by counting their reports. As we all realize, they use them much more often than they offer recovery reports to the NGS.

 

Agreed. In my area, it is not unusual to arrive at a station where the several-centimeter-deep disk has been exposed and the survey tape on the post looks "fresh". Occasionally, a station has a tripod set up.

 

On the other hand, there are days like Wednesday when I visited over twenty sites and only one recent use was evident. (Granted, when the disks are embedded in a wall, one cannot tell if they have been utilized.)

 

-Paul-

Link to comment
Wow, then Geocac is 50% of the recoveries in your area in the last few years.

Yes, but to be fair, the DC area has quite a few active benchmarkers. There are certainly other parts of the country where GEOCAC reports represent a significant percentage of recent NGS reports, but I would guess that in the vast majority of counties, we are a non-presence.

 

-ArtMan-

Link to comment
Agreed. In my area, it is not unusual to arrive at a station where the several-centimeter-deep disk has been exposed and the survey tape on the post looks "fresh". Occasionally, a station has a tripod set up.

 

On the other hand, there are days like Wednesday when I visited over twenty sites and only one recent use was evident. (Granted, when the disks are embedded in a wall, one cannot tell if they have been utilized.)

 

-Paul-

Almost all of the GPS-observable stations that I visit seem to be used, since there's usually paint or flagging or sometimes even a fresh stake placed nearby.

 

I've even noticed flagging at some benchmarks that I would never have suspected were still useful -- some old monel rivets set in crumbling culverts.

Link to comment

M&H Taylor,

 

Here let me sort through this with you... I'll repost and answer as I sort through.

 

> Our understanding is that if a set of horizontal coordinates is ADJUSTED, then pro gear can be set up on that point with accuracy to a couple of millimeters.

 

For the most part, yes. Millimeters or Centimeters depending on the station's inherent accuracy. a Pro RTK GPS sitting over a Third Order Survey Mark is more accurately positioned than the station it is sitting over.

 

> But what was the set of coordinates on which the adjustment was based?

 

In the initial sense it is a here we are, so where are we sort of process. In the old days it was optical and today it is radio but it is basically a process of Triangulation. to known points are used to derive an unknown point. Like I said before Third Order wise, that was 4 separate sets of intersected surveys. Then a least squares Adjustment, (read Calculus) is performed to place the position amongst the surveys and then the position is run against the rest of the stations in the vicinity and this can be a number of different ways... The best explanation for the process can be found here:

 

http://www.ngs.noaa.gov/PUBS_LIB/DataProcessing.html

 

> For example. PID# LW4228, Hummock 1887, on the south shore of Nantucket Island, now has ADJUSTED coordinates, to wit: NAD 83(1996)- 41 15 10.59846(N) 070 09 59.43193(W).

 

All High Accuracy Survey Data has been Least Squares Adjusted. The word Adjusted denotes the quality of the data you can expect for a given coordinate location. Posted and Scaled are other qualities as well.

 

> What was the basis for this set of coordinates? There are four “Reference Objects” listed on the datasheet: LW 4211, LW 4224, LW 4220, and LW 4235. LW4224 and LW4235 now report as destroyed. LW4211 has not been seen since 1894. LW4220 (which incidentally is about 610 feet N7.4W of LW4204, which was recovered in 2003), was first observed in 1887, and not searched for in 1955, and that’s it. So any azimuth reading from LW4228 to any of those four points is going to be at least 111 years old?

 

The referenced objects.... Those are from the part of the Datasheet called the "Box Score" It lists the bearing and distances to nearby horizontally positioned survey marks. The basis for them? Well they too have been surveyed in to what ever accuracy they have and the least squared has been performed on them too and so on. Unfortunately the stations that no longer work as active Data in the database are not pulled out of the Box Scores. The NGS Datasheet compiler does not have a subroutine to check if these stations listed in the Box Score are still active or not.

 

As to the azimuth reading? Well Probably not. Surveyors do not file a report each time they use a station. so the likelihood of there not having been a Surveyor use it in 111 years is hard to say.

 

To clarify Azimuth. Basically put, an optical survey instrument like today's total station or the older brother theodolite, does not know which direction it is facing when you first set it up. Performing a survey from the Instrument to a known position starts the process, then the instrument is turned to another known location. Learning the angle between the two known points allows the position of the instrument to be known. Then the instrument position and another known position can be used to learn the coordinates of an unknown position.

 

Stations which have an "Azimuth Mark have a Station usually set to the South about a quarter mile away to aid in speeding the process and as a local ease of use way to calibrate when making a lot of survey observations from a position. Usually only First Order and some Second Order stations had them.

 

> In this particular case, the ADJUSTED coordinates are for a point that beach erosion has placed some 500 feet offshore, so the chances of a successful recovery are quite literally dampened. But our question is still there: what was the likely basis upon which the NGS arrived at the ADJUSTED coordinates for this station?

 

They surveyed there. Really! They turned angles on that point and maybe from that point. It was likely not as eroded then. Keep in mind a few historical points. 1887 was in the pre brass disc era. It was almost around the time Steel was a new invention. This was a drill hole in a granite boulder. Tools were not Motor powered or electric powered. this was done with a Rock Drill and a Hammer. In that day the NGS was known as the Coast Survey and they were likely working to survey the coastline as they found it in 1887... In 1955 they didn't find it as you know. Today, look at how far you say the coastline is from that position.

 

Nothing's Forever.

 

> Thanks again for your expertise and clarity.

 

Anytime.

 

Rob

Link to comment

We'd have been quicker to thank you again, but have been digesting, not swiftly, the article you linked us to. Many thanks again.

 

As to your last answer, certainly they could have surveyed an offshore or nearly offshore mark. In this particular case the mark was set on the island proper, on a knoll between the sea and Hummock Pond. It was a granite post with a hole drilled in the top, and its length was between 18 & 36 inches. But up on the Maine coast we know there are marks that were made with considerable water between them and anything much like dry land. The erosion of the south side of Nantucket has been somewhat dramatic (humanly, not geologically) over the past century.

 

Cheers,

m&h

Edited by m&htaylor
Link to comment

FLASH! USPSQD DISCOVERS GPS.

Adds Coordinates to Recovery Reports

 

I was reviewing the May loads at the NGS site and I noticed that a USPSQD hunter in North Carolina (using the initials JV) has added GPS readings to each of his reports. This is the first time GPS coordinates have been inserted with the usual RECOVERED AS DESCRIBED reporting from this agency.

 

The individual is using the ddmm.mmm setting on his/her receiver. But that's okay. It's a start!

 

They say that imitation is the most sincere form of flattery. :)

 

-Paul-

Link to comment
FLASH! USPSQD DISCOVERS GPS.

Adds Coordinates to Recovery Reports

 

The individual is using the ddmm.mmm setting on his/her receiver. But that's okay. It's a start!

LOL!

 

By the way, just to chime in here, when I'm providing coordinates for a mark that has previously only had a SCALED location, I use the same or similar wording as others have mentioned: "Handheld GPS coordinates DD MM SS.SSS (N) DD MM SS.SSS (W)". Hope that helps.

 

Patty

 

p.s. Paul, the email address you have on file with Geocaching.com isn't working. I tried to send you a message about something a couple of weeks ago and it bounced with an "unknown user" message.

Link to comment
Paul, the email address you have on file with Geocaching.com isn't working. I tried to send you a message about something a couple of weeks ago and it bounced with an "unknown user" message.

 

Thanks for the "heads up". Messages were coming through from GEOCACHING over the weekend, but I can see why there might have been a problem a few weeks ago.

 

The GEO mail reflector points to an address on AOL and your correspondence may have been caught in the major rework they did on the mail system last month. Please try again, sometime. I love hearing from others in the hobby!

 

-Paul-

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...