State Plane Coordinates with Cheap Handheld GPS Receiver

#1 · July 5, 2010, 3:28 pm

Quote from Kent McMillan on July 5, 2010, 3:28 pm
This is a topic that was recently discussed elsewhere, but I thought I'd mention it again. If you have one of the now vintage Magellan handheld GPS receivers such as the SporTrak, Meridian, or eXplorist units that will accept a "User Grid" projection and will display those User Grid coordinates as the main coordinate system of the display, you can configure the receiver to display State Plane Coordinates in whatever length unit you wish.

Here's a link to a page that explains how to do it and that gives a link to a spreadsheet with the various projection parameters you'll want to use.

State Plane Coordinates with a Magellan handheld GPS

Note that only one User Grid projection can be stored at a time, so if you change zones, the new parameters need to be entered. This takes just a couple of minutes.

The 2004-vintage Magellan SporTrak I use is WAAS-enabled and generally displays NAD83 coordinates in the Texas Coordinate System that are generally accurate within about 7 ft. in Northing and Easting. Part of that is the systematic offset between ITRFXX and NAD83(CORS96), i.e. the handheld is really returning ITRFXX coordinates, not NAD83. I haven't made a careful test of this or bothered to figure out what minor adjustments to the projection parameters would minimize the offset effect since for corner search if I can navigate within about 7 ft. of a corner in a rural area, I can find it and many of the 19th century surveys have errors in them larger than that anyway. A more industrious person could fine tune things.

The other feature that is exceptionally useful is setting up the navigation display to show crosstrack error on a route. To walk a line between two points, the coordinates of the points are entered as waypoints for a route and the route is activated. That is also exceptionally useful for recon and search.

It isn't clear whether any of the current generation of inexpensive Magellan handhelds allow the use of the User Grid projection feature in this way. I understand that the Tritons, for example, do not. This may well be a case of the older technology actually serving the purpose better than the new. I discovered that one can still buy new SporTraks on the internet for about $125.

This is a topic that was recently discussed elsewhere, but I thought I'd mention it again. If you have one of the now vintage Magellan handheld GPS receivers such as the SporTrak, Meridian, or eXplorist units that will accept a "User Grid" projection and will display those User Grid coordinates as the main coordinate system of the display, you can configure the receiver to display State Plane Coordinates in whatever length unit you wish.

Here's a link to a page that explains how to do it and that gives a link to a spreadsheet with the various projection parameters you'll want to use.

State Plane Coordinates with a Magellan handheld GPS

Note that only one User Grid projection can be stored at a time, so if you change zones, the new parameters need to be entered. This takes just a couple of minutes.

The 2004-vintage Magellan SporTrak I use is WAAS-enabled and generally displays NAD83 coordinates in the Texas Coordinate System that are generally accurate within about 7 ft. in Northing and Easting. Part of that is the systematic offset between ITRFXX and NAD83(CORS96), i.e. the handheld is really returning ITRFXX coordinates, not NAD83. I haven't made a careful test of this or bothered to figure out what minor adjustments to the projection parameters would minimize the offset effect since for corner search if I can navigate within about 7 ft. of a corner in a rural area, I can find it and many of the 19th century surveys have errors in them larger than that anyway. A more industrious person could fine tune things.

The other feature that is exceptionally useful is setting up the navigation display to show crosstrack error on a route. To walk a line between two points, the coordinates of the points are entered as waypoints for a route and the route is activated. That is also exceptionally useful for recon and search.

It isn't clear whether any of the current generation of inexpensive Magellan handhelds allow the use of the User Grid projection feature in this way. I understand that the Tritons, for example, do not. This may well be a case of the older technology actually serving the purpose better than the new. I discovered that one can still buy new SporTraks on the internet for about $125.

#2 · July 5, 2010, 3:43 pm

I'm trying to work out something similar with my iphone. the "GPSkit" application has a way to upload waypoints. It seems that most users are running or biking and sharing trails, but it might just work. I was hoping to play around with the uploader today, but have to finish some maps first.

I have a Garmin 76S that I did a user defined grid on a while ago, but I haven't used it much, might have to dig that out too.

#3 · July 5, 2010, 3:52 pm

Lambert User Grid Projections

> I have a Garmin 76S that I did a user defined grid on a while ago, but I haven't used it much, might have to dig that out too.

As I recall (from about six years ago, though), the Garmins would handle user grid projections as long as they were Transverse Mercator. They weren't configured for One or Two-Parallel Lambert projections, which is what many SPCS zones, including Texas, are based upon.

#4 · July 5, 2010, 4:10 pm

Lambert User Grid Projections

Again, seems like this would surely become the next hot app for cell phones, at least for our interests.

Kent, do any of the Delorme products do what we want?

dla

#5 · July 5, 2010, 4:20 pm

Lambert User Grid Projections

> Kent, do any of the Delorme products do what we want?

I don't know, but would like to find out. The utility of an inexpensive handheld GPS unit that operates in some meaningful rectangular coordinate system is huge. The Magellan's have a couple of annoying features, one of which is defaulting from Feet to Miles rounded to the nearest 0.01 for all navigation distances > 0.10 miles.

#6 · July 5, 2010, 4:29 pm

Lambert User Grid Projections

I have also found the “handheld” (resource/recreational grade) GPS units to be very useful for reconnaissance purposes recently. Getting to with a few meters of your “search position” without running a FORMAL Coordinate into the site is a real time saver (I drive, Spud runs the Garmin). When we get “close,” we bail out and hike to the search position.

I have approached it a little differently than Kent does (although the results are similar).

I simply wrote a small program (in BASIC) that takes my PROJECT COORDINATES (SPC, LDP, etc.) and generates the corresponding NAD83 XYZ values, transforms these to ITRF2000 XYZ via the 14 parameter transformation, and then computes the WGS84/ITRF2000 UTM Zone 'X' values thereof.

The input “heights” (elevations) can be VERY approximate without degrading the final solution in any practical sense, and EVERY handheld will handle UTM Coordinates without any user input.

Like Kent, I would like to see Magellan, Garmin, et. al., improve their support for “user defined coordinate systems,” but in the mean time, this works well for me.

Loyal

#7 · July 5, 2010, 4:34 pm

Geocaching

>I would like to see Magellan, Garmin, et. al., improve their support for “user defined coordinate systems,” but in the mean time, this works well for me.

The funny thing is that Magellan has brought a specialized handheld receiver to market that is configured for the geocachers. Apparently, the surveyor market is either too small, too segmented, or Magellan thinks we all should spend a few grand on Mobile Mapper instead.

#8 · July 5, 2010, 5:10 pm

Geocaching

"Apparently, the surveyor market is either too small, too segmented, or Magellan thinks we all should spend a few grand on Mobile Mapper instead."

I think that you have hit the nail on the head Kent.

Surveyors ARE a very small market, and handheld devices such as those we are discussing have only limited application in our work (albeit a very useful one at times).

I keep hearing rumors of TRUE sub-meter (autonomous) “el-cheapo” units on the horizon (still a few years off), and that will alter the paradigm significantly.

Just ANOTHER reason to keep ALL PROJECTS in georeferenced (NSRS compatible) coordinate projections.

Loyal