Has anybody done experiments with the WAAS on the ProMark2?

Yesterday I stood on a known position with the ProMark2 attached to a prism pole with the external antenna hooked up. In Navigation mode, I watched what apparently are the terse WAAS messages on the Position Screen for a few minutes but the position displayed (NAD83 state plane coordinates in feet) never got any closer than about 38' of the control point.

Then I disconnected the external antenna and watched with disappointment that no change occurred.

The reading materials pertaining to the various WAAS related screen messages on the PM2 are nonexistent.

Not one word in the MAP 330 User Manual talks about WAAS.

Only brief mention in the ProMark2 Survey System User's Guide for Surveying was found stating: "ProMark2 includes the capability to utilize the WAAS..." (page 13). Table 1.1 (page 12) indicates that with the external antenna, one can navigate within an accuracy of less than 3 meters. However nowhere else in any of the three manuals (ProMark2 Survey System User's Guide for Surveying, MAP 330 User Manual or the Ashtech Solutions User's Guide can I find further instruction, reference or even mention to WAAS and how it pertains to being used with the PM2.

When I asked tech support if there was any further information available from Ashtech about how the PM2 is to use the external antenna for navigation (with WAAS), the reply was; no.

After visiting the FAA's web site, the reader can get the idea of WAAS but no real insights as to how the ProMark2 will behave regionally.

I'd be very interested in hearing from somebody that can describe what all of the WAAS messages that are displayed mean and exactly why disconnecting the external antenna made no difference in the displayed position while in Navigation mode.

Kelly,

I don't remember exactly how much I had to tweak the parameters in the PM2 to get it to output very close SPC's but it was on the order of 40-50'. What I did was to just change the false northing and false easting until it got close. There doesn't have to be a whole lot of trial and error to get there either, the PM2 will allow you to display your SPC and geodetic (lat/long - set to NAD83) coordinates at the same time. Simply scribble down both numbers while the unit is running (doesn't matter how accurate the position is on this technique, you're looking for the relationship between the two numbers). Run the lat/long through corpscon or someother trustworthy coversion software and see the difference between the SPC and the lat/long SPC. Whatever the difference, is adjust your false northing and false easting to fit. Since the lat/long display is only out to the 5th decimal place, lack of significant digits comes into play (you could be off in your tweak factor by 4-5 feet due to the rounding of the geodetic coordinates). So a little extra refinement has to be made, this is the trial and error part. Set the unit up in a static set up and let it run in navigate mode for some amount of time (5-60 min) on a known point. The unit will average the position. Scribble down the offset from your known coordinates. After you have done this several times on several days you should have a reliable offset to further tweak your false northing and false easting. This should be the same for all the units so you don't have to go through the experimentation process on each of them. A word of caution though, as you might imagine the further you get from where you derived your tweak factor the more potential for error there is. So I would suggest only using this for reliable coordinates within 20 miles (just a guess - I know it works to spec within that). Also Ashtech did not come up with this and I am rather sure that they would not condone this method so don't hold them to it.

As for the WAAS messages the only ones I know of are the one stating that a lock on WAAS has been achieved (which can sometimes takes several minutes) and that the unit is WAAS averaging the position.

Hopefully in future firmware refinements Ashtech will improve the user coordinate system feature. It is very useful. We use it on large boundaries to assist in corner search. We have found on average that it positions to 10' in WAAS and the worst I have seen is about 15'. Of course you have no way of knowing this (stats) so it would be hard to rely on for something more than "navigation"

Hope this helps
Shawn Billings
SIT Texas

I haven't had as much testing on Magellan GPS units, but under Garmin you can get exact user grid parameters for SPC (yes and in feet too) for the Mercator Zones. I can tell you what they are, as I built a spreadsheet for all SPC TM zones. I would bet these would work in the Magellan's also as my quick look at one it looked more flexible than the Garmin, including Lambert projections etc.

That being said, I did not find a quick exact solution for creating a SPC simulating Lambert Zone. I didn't try too hard though it might/should be possible.

If I get a chance to borrow a magellan and if the PM2 unit is similar as I expect, I could say better.

If you would like my values to try let me know...

Kelly,
I have the NOAA Manual "SPC system of 1983" in a .PDF format if you think you might need it. Also, make sure you put the User Grid Constrants in decimal.degree format.

I will agree with Shawn, I had to do some minor "tweaking" to get very close. Right out of the box I was getting within 10'. Now after some adjustments to my origin I am usuall within 5'.

Dean

Thanks guys for the tips and hints - albeit a tad off topic (was WAAS afterall ;)

Dean, yes, I already have that paper written by Mr. Stem - excellent article. Here is the link to the file in case anybody else wish to download a copy:

State Plane Coordinate System of 1983 - NOAA Manual NOS NGS 5 (pdf format)(January 1989)

Do you do the same technique-tweak that Shawn discribed?


Jerry, yes please, I'd be interested in looking at that spreadsheet. If it isn't too much bother, maybe post it somplace where we could all download it from.

Shawn and Dean, are you using the external antenna hooked up to the ProMark2 while in Navigation mode and in search of the anticipated corner or are you doing your recon without the external antenna?

I use the same method as Shawn discribed in my tweak method as well as using the old "well lets see if this works" method;). I use the external antenna to help me find my state plane monuments.

Hi Dean,

Have you tried any experiments with and without the antenna hooked up to the ProMark2 to see the effect of WAAS in Navigation mode?

Did you say "experiment"?

Don't you know we don't do that around here??????


jd

Experiment is just another word for experience...
Bet you blew up the high school lab just like I did...
Lotta fun shooting corks from them bunsen burners with a 'capped' flask though....
Come to think of it...This is probably why dogs have a natural instinct to bark at us...We're cat people (at least from our inquiring nature)...

More manufacture's should just send us any type of equipment...We'll let em' know what will work and what won't...Guess Phil can keep that up on the Ashtech end...He's the original 'sperimenter'....

TM

And sadly, I don't think our RTK is going to make it in our normal budget..Heard today, that a straight across the board 10% cut has been ordered. But we have a mandated drainage study that it might be purchased with, so there's still hope..

Now, it seems, experiments that result in a 3' diameter fireball are failures ;)

Don't eat Jalapeno Pintos the day before burning brush piles.....

When I typed WAAS on the address bar of my browser the result was 20,972 hits.

It's certain that not all of them are relevant but I found a little light reading at this location.

http://gps.faa.gov/Library/library.htm

Since the WAAS is an FAA project I figured they might know a little something about it.

As far as some of this info that relates to the NON-survey capabilities, you will probably find more info on consumer GPS user sites and on magellangps.com for the 330. For example:

WAAS info

While Kelly's original question could be an operational problem, or a characteristic of the unit, or even WAAS it seems more likely that the issue was trying to use user grid which may or may not be set up right.

The example doc given on the ashtech ftp site only seems to cover a lambert zone, so if you are in a mercator zone and follow that obviously going to run into confusion.

The first thing to do to see if WAAS coordinates are working is to be comparing lat longs or straight UTM's and not complicate things with the user grid issues at the same time in my opinion.

Can you tell me WAAS coordinates don't check into a NAD83 control point by 8 meters in lat long? Also as Mr. G often reports in here, WAAS corrections are in WGS84 so they will differ a meter or two from NAD83 even if the world were perfect.

- jlw

You are correct Jerry. It could have been any one of those things that you mentioned. I'll attempt to test which one was most likely.

The ProMark2 was first setup over a known point (NAD83 44°32'40.29808"N, 68°25'01.71217"W, elevation 147.429 NAVD88 - MESPC83, Eastern Zone (1801), 320000.846N, 1005850.886E) in Navigation mode with the external antenna hooked up.

It was allowed to set for 10 minutes while the WAAS message indicated WAAS Avg. After 10 minutes the position (NAD83) displayed in the secondary position screen was 44°32'40"N, 68°25'02"W

Because the ProMark2 conveniently allows two coordinate systems to be simultaneously displayed and I had previously set the user grid to SPCME83 (1801), the position displayed in the primary position screen was 010-05-860E (+9), 003-20-011N (+10), 173 FT. (+26).

After the first 10 minutes, I unplugged the external antenna and waited about 12 minutes. Everything else about the setup remained unchanged. The position displayed in the secondary position screen was unchanged (44°32'40"N, 68°25'02"W). The position displayed in the primary position screen was 010-05-848E (-3), 003-20-017N (+16), 173 FT. (+26). So it grew further away in the northing, but actually improved in the easting.

After waiting an additional 15 minutes (still unplugged from the external antenna), the position displayed in the secondary position screen was 44°32'41"N, 68°25'02"W. The position displayed in the primary position screen was 010-05-844E (-7), 003-20-025N (+24), 178 FT. (+31). So it grew further away in both the northing and the easting.

Next, the antenna was plugged back. I noticed that the WAAS Avg. timer started anew. After waiting 60 minutes, the position displayed in the secondary position screen was unchanged at 44°32'41"N, 68°25'02"W. The position displayed in the primary position screen was 010-05-844E (-7), 003-20-021N (+20), 176 FT. (+29). So it improved by 4' in the northing and remained unchanged in the easting.

Lastly, the external antenna was unplugged from the ProMark2 at 6:20 PM EST. The WAAS Avg. timer kept going, but for an unknown amount of time. At 7:30 PM EST, the WAAS Avg. timer displayed only 21 minutes. The position displayed in the secondary position screen was unchanged at 44°32'40"N, 68°25'02"W. The position displayed in the primary position screen was 010-05-835E (-16), 003-19-999N (-2), 204 FT. (+57). So it improved by 18' in the northing and grew further away in the easting by 9'.

It seems curious, that while the external antenna was unplugged, the position displayed was actually closer to the known position than when it was attached to the ProMark2.

As for the differences between WGS84 and NAD83, Ashtech Solutions reports absolutely no change in the processed latitude and only .00001" change in the longitude for the known point.

Therefore, the data seems to suggest that the full effects of WAAS might not reach this eastern region of our country or the unit isn't processing the WAAS signals correctly.

Incidentally, setting up the user grid for a transverse Mercator coordinate system is fairly simple once you have the proper values (thanks Richard and Mike). If you want it to display SPC in feet, go to the Setup Menu, choose Nav units, then Miles/MPH. Then from the Menu, select Map Datum, -> Primary, -> NAD83. Next from the Menu, select Coord System, -> Primary, -> User Grid, -> Trans Merc, -> enter the lat of origin in degrees.decimaldegrees, -> ditto for long of origin, -> enter Scale factor 1-(1/x), wherein x is 10000 for Maine East (1801), so 1-(.0001) = a scale factor of 0.99990000, enter the Unit to meters conv value, for U.S. Survey Feet the reciprocal of 3.28083333 or 0.38480061, enter the False easting and northings at origin in feet, 00984250.0 and 0.0 respectively for Maine East (1801) and you're done.

Well I would bet that the accuracy of your user grid can be probably be checked by entering lat long values in your primary and reading the results in secondary system.

The user grid can only be set up as the Primary coordinate system.

Kelly on my Garmin we only have one system at a time, so I set to NAD83 dms and enter waypoints around the zone to check, then toggle to user grid and read out the values for those points to check. This will probably work on a magellan also.

- jlw

Kelly,
Sorry for the delay. Yes I have done some testing without the external antenna and I find some 5' to 10' diff. between the internal and external ant. I have not done the one hour navagation testing like you have. I have done walk ups to the known point with the external and without.