ArcPad Elevation errors

[KenSwinson]

I recently collected elevation data with a Trimble GPS setup running Arcpad and the Trimble Positions software said my accuracy was 4 inches. When I get the ArcPad elevations in HAE and add the geoid height for that location using the NOAA website, my elevations are about 4 feet too high. How do I know this? Because the site was previously surveyed a few years ago and I am using that data to compare with my recently collected data. I spoke with a local GPS rep and he said that ArcPad will always give you bad elevation data, regardless of what others say, it is not right. He has run into the same problem before.
Has anyone else run into this issue? And is there a way to fix it or am I doing something wrong?
Has anyone ever used ArcPad to collect a position over a known benchmark and compared the elevations?

Thanks,

Ken

[MatthewKing]

Ken,

Were you ever able to figure this out?

-Matt

[KenSwinson1]

Yes and No!
I actually tested the system with ArcPad to collect a position over a known benchmark to compare the elevations and it was not good. I cant find my results right now, but I will go through what I did.
I used a GeoXH 6000 with external Zephyr antenna that had both TerraSync and ArcPad. I set up on a local benchmark and collected a point with Terrasync, then closed it out opened ArcPad and collected another point. The point collected with TerraSync was all within the expected horizontal and vertical accuracies, but the point collected with ArcPad was only acceptable within the horizontal accuracies. The vertical was several feet off and I could not identify why. The offset was not from geoid heights or different vertical datums, it was just wrong. So I would not use ArcPad if you want accurate vertical elevations.
I hope someone else could chime in on this as I would suspect many people are using this setup and think they are getting good data, but are not.

[CraigGreenwald]

ArcPad would just be reporting the HAE, in meters, as reported by your receiver -- UNLESS you have values set in the GPS Height tab of GPS Preferences.  Values you set there will affect the reported elevation.

Now - is your map datum WGS 1984 or is it NAD 1983?  If it's WGS 1984, then ArcPad is absolutely not adjusting the elevation from the HAE reported directly from the receiver (again, unless you have values set in the GPS Height tab).

If it's NAD 1983, there there will be a very slight elevation adjustment with the datum transform, but on the order of mm (maybe cm) since GRS-80 and WGS 1984 ellipsoids are nearly identical.

I would love to help you dig in deeper if you want me to.

Also, please note that we wrote an extension to ArcPad that handles the high accuracy WGS 1984 to NAD 1983 (2011) transformation as well as HAE to MSL elevations using Geoid12a.

The extension is called GeoBullseye: Mobile GIS Experts : GeoMobile Innovations : GeoBullseye For ArcPad