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gpsblake

Which format should I use to report GPS coordinates to the NGS

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I've been submitting my handheld GPS coordinates for SCALED benchmark locations using the

 

DD MM SS.xx format example N 80 00 00.00

 

I've noticed browsing through various reports that many, including a lot of Power Squadron use the common geocaching format of

 

DD MM.xxx format example N 88 00.000

It would be much easier to use this format because I wouldn't have to convert it to the other format.

 

Question:

Which format should I be using?????

Edited by gpsblake

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Question:

Which format should I be using?????

 

Look at the NGS datasheets and you'll see their standard, which is DD MM SS.xx

 

I made the conversion from the "Geocaching standard" to "NGS standard" a few months ago.

It's easier when we all use the same language.

 

~ D.R. ~

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What kind of handheld do you have that gives you dd mm ss.ss with two decimals? I want one.

 

0.1 second is about 10 ft north/south or 7 or 8 ft east/west (depending on your latitude). Most handhelds even with some averaging only achieve about that accuracy. I keep wanting to do long averages on multiple days to get some points more accurately, and the display resolution on most units gets in the way. I use dd.ddddd format for those cases and manually convert, but that is still almost 4 ft increments. I would have to put a huge effort into averaging on many days before I presumed to give NGS values to 0.01 second.

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So I've been using the correct format, which I thought was the standard.

 

I use geocalc to convert from the "geocaching" format to the format that the NGS uses. It gives the seconds down to .00 when converting & do I cut and paste.

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I usually don't include my handheld coordinates on my NGS log entry. But when I do, I make it in DD MM SS.S format. I figure that if I can get within 20 feet or better with 15 to 20 minutes of averaging, it's better than the "Scaled" +/- 6 seconds.

 

And I do the same as Bill93, I change my format over to DD.DDDDD on my GPS and let that average out. I than convert that over to DD MM SS.S manually.

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gpsblake:

 

Bill's point might have slid by you. With a consumer grade GPSr, we shouldn't use two decimal points on seconds. Yes, that might be what you get from a conversion program, and the handheld calculator I prefer to use will give me even more decimal places. There is a subtle difference that many engineers (and others) will understand between accuracy and precision. In any case, just one decimal place on the seconds will be fine in this case. Since you get two places from the conversion software, I suggest you just round to the nearest one decimal place of the seconds.

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I may be the only one who generally uses UTM for defining waypoints and searching in the field. It's much more intuitive (for me) to know I'm x meters north and y meters east of something, rather than looking at the DD MM SS.S and trying to remember how long a scond is (thanks for repeating that Bill93). It's also the most precise way the unit displays a location. More precise than it is accurate (except maybe for long averages). Interestingly, for horizontal control stations the NGS datasheet also incudes UTM, precise to a millimeter (and I'm sure the location is not that accurate).

 

However I would not put the UTM coordinates in a log. In fact I have never put any coordinates in a log. For tri-stations it's unneccessary, and I usually don't even bring a GPS for most stations, certainly not if I'm hunting a lot of bench marks.

 

Today I was hunting some old city monuments (monuments placed where future streets were to run) and I used the GPS to look for them (with very little success). These are sort of like boundary monuments and their coordinates are not published (or known). I guess I will put in the GPS readings if I ever log these somewhere.

 

my 2 cents

Edited by Papa-Bear-NYC

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Fair enough on the coordinates being down to 1/10th of a second. I just posted down to the 1/100th of a second just to maintain consistency with their current format. The only argument is that the MM SS.x could be mistaken as MM.xxx and like I posted, the local power squadron uses the MM.xxx format in their recoveries.

 

I do think putting in GPS handheld coordinates on benchmarks that are scaled are a very important bit of information for future recoveries, especially if the benchmark is off by several 100 feet on the scaled coordinates.

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Hi, GPSblake:

 

The Power Squadron is using Degress and Decimal Minutes up here in North Carolina, also.

 

You're doing a great job in your state. The GPS unit and the bicycle make a great combination! :lol:

 

Keep up the good work....the S.C.G.S. knows that GEOCAC reports can be relied upon!

 

-Paul-

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Thanks PFF. I hope to sneak across the border to recover some NC benchmarks in your state.

 

I love the idea of using my bicycle to track down benchmarks, I get good exercise doing it and I can safely ride the bike right up to the benchmarks safely unlike a car where I've got to find a safe place to park.

 

Your idea of using a safety vest has already come in handy. Not only for benchmark hunting but for bike riding.

 

I also just realized today, I've now found more BM's than geocaches.

 

Cheers and thanks so much for your time & knowledge into the hobby.

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I don't think it's a big deal one way or the other, but I've always used the DD MM SS.S format in my NGS reports, since DMS is the format they use on their datasheets, and it seems all the coordinates on the datasheet should be presented in the same format.

 

-ArtMan-

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They have a standard on this. It starts out something like HTT1 or 2, depending on the quality of the GPS unit and specifies how you should format the numbers. Hopefully somebody knows where it is on their site. I've done some in the past in decimal, but that's bad because DMS users might not notice and will make a mistake. Handheld consumer GPS units often produce their best resolution in the decimal format, so use that and convert before doing the NGS sheet.

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Actually it's HH1 and HH2.

 

HH1 is accuracy +/- 1-3 meters as provided by differentially corrected, hand-held GPS. The reporting format is [D]DD MM SS.ss (two decimal places).

HH2 is accuracy +/- 10 meters as provided by stand-alone, hand-held GPS. The reporting format is [D]DD MM SS.s (one decimal place).

 

See, for example, http://www.ngs.noaa.gov/AERO/Genspecs_A/Vo...hment%201-6.pdf, http://www.ngs.noaa.gov/PROJECTS/INSTRUCTI...OD/SOW-apxH.pdf, or http://www.ngs.noaa.gov/ContractingOpportu...eling_sow9a.pdf (which refers to X and W, rather than HH1 and HH2).

 

-ArtMan-

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Thanks ArtMan! My recollections are usually in the right direction, but the details can be a bit fuzzy. I should take up drinking so I have something to blame it on :ph34r:

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Photobuff,

 

You might try a shot or two of 80-proof Old Google, aged on the [server] farm, rooted in the fertile Santa Clara Valley. It worked for me!

 

-ArtMan-

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Just did a little bit of math on rounding the DD MM SS.xx format down to DD MM SS.x

 

Say you convert the DD MM.xxx format to DD MM SS.xx with geocalc and come up with the following.

 

N 33 44 00.05 W082 12 35.05

 

Your accuracy is 6 feet with WAAS enabled with averaging.

 

Now you round it down to N 33 44 00.0 W 82 12.35.0

 

The distance between the .05 sec and .00 sec is 9 feet.

 

So therefore you just decreased the accuracy of your report from 6 feet to 15 feet by rounding to the numbers to the tenth of a second.

 

Comments????

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In very rough numbers, a minute of latitude is a nautical mile (6000 ft). Divide by 60. A second is 100 feet. A tenth of a second is 10 feet. You really can't expect much better on a good day from consumer level handheld GPS receivers. To continue: One hundredth of a second is one foot. You kidding youself and others if you use two decimal places of seconds. What you convert from is not really relevant.

 

And yes, a minute of longitude in the northern US is a lot less than 6000 feet. And even Latitude is less than 6000 ft away from the equator. That just makes the above discussion even stronger.

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Well, I did one more thing and I'll reverse myself again and do the 1/10th of a second format but without converting from the geocaching format of MM.000

 

In my great wisdom (laugh), I discovered I can make my Garmin GPS shows the SS.x format but it doesn't show a SS.xx format. I went to a local BM I already recovered, let it average using that got the EPE down to 6.2 feet. Compared to the adjusted coordinates, it was 2 feet off. I'll simply in the future just set the GPS to use that format and just directly copy from the GPS rather than convert using geocalc.

 

But my point of rounding when converting does decrease the accuracy of the radius greatly. If you have a accuracy of 6.0 feet, the search radius is going to be 36x3.14 = or 113 square feet. If you have an accuracy of 13 feet if you decided to round the numbers, the search radius is 169x3.14 = 530 square feet, nearly 5 times the area.

 

Anyhow, enjoyed the discussion about this. Now if we could get the Power Squadron on the same page when they publish their coordinates.

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I use decimal degrees in the field because the GPS display reacts much faster to small movements. Trying to watch the compass-type "arrow" was driving me Nuts! Now, I simply move a little one way and another, until the coordinates match exactly.

 

Once I have the exact position displayed in the GPS unit, I turn on the metal detector. If I'm not standing directly on the disk (as is sometimes the case), I'm within a couple of feet.

 

To avoid having to calculate every mark, individually, I enter the DDMMSS.S coordinates into the map program. Then I switch the PREFERENCE to Decimal Degrees. Mapsource displays a list of marks by name, and gives the position. I copy and paste this into an Excell spread sheet, which I print and carry with me.

 

The only "conversion" that is needed is if I take an averaged reading on a benchmark with SCALED coordinates. Upon returning home, I use the calculator at http://www.gpsvisualizer.com/ to give me DDMMSS.s for NGS reports, and DDMM.MMM for geocaching.com/mark entries.

 

(I feel it is a courtesy to use the DDmm.mmm format on geocaching.com/mark, for the benefit of casual users who only consult this database, and/or who want things in the identical format as the caches they are hunting during the same trip.)

 

-Paul-

 

Food for thought: Could the fact that the US Power Squadron does not switch their GPS receivers to display DDMMSS.S account for the large number of "Not Founds"?

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(I feel it is a courtesy to use the DDmm.mmm format on geocaching.com/mark, for the benefit of casual users who only consult this database, and/or who want things in the identical format as the caches they are hunting during the same trip.)

Paul,

 

Just to clarify, when you enter your coordinates at geocaching.com in the form provided for that purpose, they give you several format options for data entry, but then your coordinates are displayed in their preferred format.

 

If you're talking about entering coordinates in a free-form text block, then I'm sure your standardization is appreciated by many.

 

I, on the other hand, use DDMMSS.s exclusively for benchmarks to be consistent with what I see on the NGS datasheets. For that reason, and to avoid possible conversion errors, on the rare occasions when I enter coordinates as text, I do so as DDMMSS.s.

 

-ArtMan-

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Just to clarify, when you enter your coordinates at geocaching.com in the form provided for that purpose, they give you several format options for data entry, but then your coordinates are displayed in their preferred format.

 

 

Hi, ArtMan:

 

Yes, I was referring to the text block entry.

 

Can someone give me an example of an entry where the Add a Waypoint feature was used? How does it appear in the data sheet; i.e., is it obvious, or is using the text box better?

 

-Paul-

Edited by PFF

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I read something last week and now I can't seem to find it.

It has to do with significant numbers.

If It has the extra decimal point or second it is a significant number.

 

And thus reported that way.

I am still wondering if it is really of use for the puposes of the NGS.

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Can someone give me an example of an entry where the Add a Waypoint feature was used? How does it appear in the data sheet; i.e., is it obvious, or is using the text box better?

 

Okay. Here's an example for a scaled benchmark. LY2080

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