shrug-l: RE: Lat/Long Tool

Sykes, John John.Sykes at
Thu Jun 12 09:45:24 EDT 2014

The idea is eliminating error from calculations.  The "standard" precision for fixed geographical locations in the USGS Bluebook is DMS with 5 decimal places.  In Florida, that is roughly 1mm.  This tool shows DMS to 6 decimal places.  I have used it to check the accuracy of plotted data and it is accurate to that level of precision plus a protection digit.  I don't think any of us using it believe the 13 decimal places in the DD readout.  My calculator will only take 9.  But if you take that 9 decimal places DD result and convert it to DMS, you get the 5 decimal place precision that the USGS uses in the Bluebook.

I've used the tool several times to check the plotted location of a CORS station or a USGS monument in ArcGIS and it is dead on, if you zoom in tight enough.  In actuality, though, I think that Julie (who wrote it) just didn't bother to round the floating point numbers to any given precision, but left it up to the user.

By the way, there is talk that with the new high-accuracy atomic clocks (1000 times more precise than current ones), that GPS may eventually be eclipsed by a system that will tell you where you are anywhere on the face of the earth, without any external reference.  Right now, good GPS survey data will get you to about 1 cm horizontal and 2 cm vertical accuracy in Florida with an hour of data acquisition, this new system could give you mm accuracy in both dimensions with virtually instantaneous data (ok, maybe 1 second).  It would make self-driving cars and auto-landing aircraft routine.

But getting back to the subject, I think the major advantage is that it eliminates one source of error almost completely.  You can then concentrate on the other errors of the various layers in your map.

-- John

From: shrug-l-bounces at [mailto:shrug-l-bounces at] On Behalf Of Jim Robeson
Sent: Thursday, June 12, 2014 9:18 AM
To: 'Peterson, Lance'; shrug-l at
Subject: RE: shrug-l: RE: Lat/Long Tool

GPS, clearly is not.  In the moving of data back and forth from system to system you do get rounding.  Over the years positional dada can move.  13 decimal places is a case of just because you can, should you?

Jim Robeson

James M. Robeson
Mapping/GIS Sales, Trimble Certified Trainer
Jim at<mailto:Jim at>
Direct (850) 656-6075

[cid:image003.jpg at 01CF349E.EF731ED0]<mailto:Jim at>

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From: shrug-l-bounces at<mailto:shrug-l-bounces at> [mailto:shrug-l-bounces at] On Behalf Of Peterson, Lance
Sent: Wednesday, June 11, 2014 10:40 AM
To: shrug-l at<mailto:shrug-l at>
Subject: shrug-l: RE: Lat/Long Tool

I find it hard to believe that GPS measurements can be accurate to 13 decimal places. For decimal degrees that would be .00001mm.

Using a greater number of significant digits in a calculation than a device is capable of measuring will just lead to false precision.

Lance Peterson
ISS Systems Developer
City of Tallahassee

From: shrug-l-bounces at<mailto:shrug-l-bounces at> [mailto:shrug-l-bounces at] On Behalf Of Sykes, John
Sent: Wednesday, June 11, 2014 9:48 AM
To: shrug-l at<mailto:shrug-l at>
Subject: shrug-l: Lat/Long Tool

Before ArcGIS 10.2, I had a dynamite tool from the USDA National Forest Service out of Santa Fe, NM, that could be added to a toolbar and would allow you to click on a point and it would give you a pop-up with the latitude & longitude to about 6 or more decimal places in the seconds field (e.g., 26° 15' 20.546947") and decimal degrees to about 13 decimal places.  Of course, it no longer works with 10.2.

Now before you say no one needs that kind of accuracy I say, wrong!  Just look at any CORS station, which is listed in DMS to 5 decimal places as is all USGS marker data.  This tool had those locations nailed to all five decimal places!

The DEP tool is less useful that the ArcGIS readout both of which are 2 decimal places in DMS format (the ArcGIS readout can give higher accuracy if used in the degrees, decimal minutes format - go figure).

GIS and GPS are getting way more accurate, we need GIS tools that have the same level of accuracy.

But enough of the preaching, the original question is, does anyone have or know of a lat/long tool with about 6 decimal accuracy in DMS mode that works with 10.2?

-- John

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