Mike Margolis and others have reported sub meter position accuracy with WAAS and/or Beacon.

What do the elevations look like?

Paul in PA

There is no vertical spec, and frankly no place in the software to enter an HI.

So, I never bothered looking at the V when I did my tests.

never mind...I was explaining how to set vertical HI for MM Pro in the MM Office


I gotta take more time reading before I try to answer

Modified By J.D. Billings on 8/9/2005 at 9:33 PM

There is a place in the Thales gps utilities where you can set the HI. I don't know if this is reflected in the Arcpad GPS analysis, though.

I'll post some results by the weekend. I'm still working on getting data collector info into shape file, without much success. I would like to see some MM CE elevation data from an external antenna.

hoping to not add any confusion to a MM CE subject, but in MM Office for the MM Pro you can set a vertical offset for the observed point(s). If you want to split hairs, be sure and use the L1 phase center of the antenna for the HI (rover) and input it as a negative number.

Not sure about ArcPad or the utils with the MM CE. But, since the CE is not curently post processed I guess that info would have absolutely no relevence to the subject.

I think that's the reason I edited my other post

In the latest performance analysis report from the FAA, all reported WAAS vertical values at the 95% confidence level were sub 2 meter. The best station results were Washington DC and Chicago at about a meter. The worst was Los Angeles at 1.676m

Sat

Thank you J.T. Al. I expect about twice my horizontal accuracy in my vertical. I was not sure though if Beacon and WAAS signals gave North, East and Up corrections.

In affect using GPS with WAAS would allow a plane to approcah a runway much more accurately than an altimeter?

The accuracy potential is there, Thales is not using it. It is definitely worth a Feature Request once users hook up there good antennas to the units.

Who has gotten a cable to hook up a ProMark antenna to an MM CE?

Have you yet J.D.?

Paul in PA
Modified By Lawrence Paul Lopresti on 8/10/2005 at 12:10 PM

We not only do not have a cable to connect an external antenna to a MM CE, we do not have a MM CE.

My caution to anyone using any "submeter" gps is to understand the difference between the displayed coordinates that you believe to be the most precise possible as related to your NAD83 SPC Zone, and the "truth". The coordinates reported by the unit will most closely resemble ITRFR coordinates - NOT NAD83. If you look at the difference in the ITRF coordinates and the NAD83 coordinates of the CORS site nearest your position you will see the (approximate) amount of shift to expect. In our immediate area the shift is N -0.61m, E +0.69m, and Vertical +1.25m.

I bet many a user has declared their units were not getting the desired results when they had set the unit for displaying local SPC's. The unit is actually displaying SPC values on the ITRF, not NAD83. Our workaround for this (also did it with the Reliance unit) is to modify the false northing and false easting settings in the unit. Also, I have MM Office set up to use the modified false northing, false easting and vertical correction. It does make a tremendous difference for us.

It's a simple thing to correct, and I would doubt that many gps manufacturers have addressed the problem yet. Many of us got really ticked off at Mr. Geo about 4 years ago what he started a thread with the title "Ashtech Solutions is Wrong". I do not think he intended to slam the actual post processing engine, rather I think he was trying to point out the error in real time WAAS positions being distorted by the ITRF/NAD83 shift. Well, it's still there and we need to address it. The MM CE is just as vulnerable as any other unit.

JD

I sat my MM CE on my tripod today over a nail that I had coords from a harn point using my locus.

Ashtech Solutions Coords:
N 1,912,575.26
E 1,192,519.87
EL 582.90

MM CE Coords:
N 1,912,576.0
E 1,192,518.9
EL 497

Coords are MS E State Plane, US Survey Feet.

Less than a minute after acquiring DGPS, waas only, I wrote the coords in my field book from the Arcpad GPS status window. The elevation started out at 494, and increased to 497 when I wrote them down. The tripod was 5' above the nail. The MM antenna height was set to the default of 1.50 meters, or 4.92 feet, in the gps settings under the gps utilities folder. I don't know if Arcpad uses this or not. I'm gonna find out first chance I get, change the height to 50' or something, and see if it changes the elevation in Arcpad. I don't know yet if it accounts for the ITRF to NAD83 shift, either, but I plan on finding out.

Arcpad GPS status window shows coords to the nearest tenth of a foot, elevation to the nearest foot, after acquiring DGPS waas correction.

Not too shabby for a short occupation real time waas only correction, regardless. The point wasn't in an ideal spot, either, trees to the south.

Ya'll get 'em while they're hot, so's ya'll can tell us dummies how to use 'em. :-)

I can pretty much guarantee you that your 497 height is an HAE, not an ortho height. As far as I can tell, Arcpad has no geoid model to calculate a decent dirt height.

You know what, I just realized it was over 100' off. I was thinking it was within about six feet! I could have wrote it down wrong, but I don't think so. Anyway, it does a darn good job horizontal. I don't really care about the vertical, anyway. Six feet or Six Hundred, I can't think much of a use for that much elevation error. Jeez, I was kind of proud of the elevation till I looked at it. I guess the antenna height is kinda irrevelant. There is a check box under Arcpad Options, Protocol, for "Use Height in Datum Transformation" that I have unchecked.

It didn't occur to me about the geoid model. I kinda regret posting it now. I read in an earlier post where somebody said the elevations were pretty close.

I'm tickled with my MM CE. The Arcpad has a lot of bells and whistles that I can't ring or blow yet, but I learn a little every time I use it. It's hard to work and play at the same time, wind up not doing much of either.

Well, I got the dummy part right....

It is a cool tool. I am also getting to know Arcpad, one of these days I need to set aside two hours and do the tutorial.

I did a demo today, these guys have been using an old racal unit with Arcpad on an iPaq. When it rains, they put the iPaq in a zip lock baggie.

They were in love with the MMCE receiver, then I showed them the bluetooth beacon and told them "no more $800/yr subscription fee, no cables and no backpack either." It was like shootin' fish in a barrel.

If the 497 is HAE (like Mike suggests) then using Geoid03 for that location would make the Ortho elevation of that point (according to the MMCE):

586.45'

This seems to agree pretty well with your 582.9'. Don't you think?

Yes, that would fit pretty well, especially if the MM isn't recognizing the antenna height default in the thales gps utility settings. Another 5' off would put it at 581.45.

I'm sure proud you thought about that and brought it up. I'm gonna change the antenna height to something drastic and see if it reflects in Arcpad. A person could go back and re-calculate points based on the geoid and probably get some decent rough elevations if they wanted to. It would be close enough for a water system model.

Sometime later I'll post some observations based on an average like it's supposed to. I just set it on the tripod, and wrote down the coords less than a minute after it started logging DGPS.

NOTE: Arcpad does not recognize the antenna height in the gps settings. I just went out, changed it to from 1.5 meters to 10 meters, and the Arcpad elevation stayed the same. So, it appears that it was a pretty good elevation after all, within 1.5 feet! Whew, I feel better. Thanks, Shawn.
Modified By J. T. Strickland on 8/11/2005 at 7:15 PM

NOTE: Arcpad does not recognize the antenna height in the gps settings. I just went out, changed it to from 1.5 meters to 10 meters, and the Arcpad elevation stayed the same.

I did the same thing today. My results were much the same:

I took three different 60 second averaged shots with Arcpad, and got three exactly same HI’s of 21.71 meters. My antenna was on a 2m pole, and the HAE at the bottom of that pole is 21.734m. That shows me that I was within two meters of truth.

Modified By Mike Margolis_ on 8/11/2005 at 9:05 PM