This is the screen showing the datum set up for the coordinate system we have in MM Office 3. This should suffice for any place in North America (no more determining approximate shifts for your locale).

So what difference does it make to overall operations?

1. You can easily set up a shape file with true NAD83 State Plane Coordinates and open that shape file with MMO and send it to the reciever without having to alter your shape file. In other words, it automatically transforms from NAD83 coming from ACAD to ITRF going to your WAAS enabled handheld. As has been discussed (to death) on this board, this takes out a systematic meter in error working with WAAS on an NAD83 project.

2. It works to convert data stored on the WAAS enabled hand held from ITRF to NAD83, again removing the roughly 1 meter systematic horizontal error you will have if you don't account for it.

3. If you set up your shape file to include the N and E of your coordinates as attributes, you will be able to view true NAD83 coordinates. Typically, if you are going to account for this error before, you had to shift your coordinates in you CAD or GIS in order to account for your local NAD83 to ITRF shift before you sent it to MMO. As such, the N and E attributes would be shifted coordinates and no longer represent true values. Now, because the N and E attributes are being set up in true (unshifted) NAD83 coordinates, they remain true through the upload process.

Some of you may not see much benefit to all of this, but trust me, the PM3 is capable of true submeter, realtime positioning using WAAS only. But because the difference between ITRF (which is what WAAS is set to correct a reciever to) is different from NAD83 by 2 meters (spacially) or about 1 meter horizontally, you can easily be off by more than a meter most of the time. It really is about squeezing out everything the unit has to offer.

Hope this helps.

Shawn Billings
Modified By Shawn Billings on 7/27/2006 at 1:07 PM

I have a similar system set up in Carlson GisCe on the Mmce. I still have to twig the false n and e to get it to work right, though. I fooled with the thing half the day yesterday. Looks like it should work right using just these parameters. I'm gonna have to do some more studying on the carlson end, I think.
Your're right, though, most of the autonoumous error in the thing is from the shift. Without accounting for it, it's generally over a meter.
thanks again,
terry
EDIT: Looks like I was wrong about having to twig the false n & e in carlson. I changed it to what it's supposed to be, and I'm hitting around a foot or two n & e. It's gonna take a little more experimenting with carlson to make sure it's working properly. Elevations are still within 2-3 meters. Not close enough for much practical use.
Modified By J. T. Strickland on 7/27/2006 at 5:04 PM