With the Kilgore contingency of the Red Neck Science Consortium en route to Oklahoma, I can only imagine what wires might be twisted together this weekend, but I am sure whether positive results or negative, the experiments will be a complete success. (Any time you come away knowing more than you did before, you were successful). I am anxious to hear of the results.

DP,
Mom and Dad left about 3ish with more trinkets than you could shake a stick at. The wagon sure looked funny with all that crap strapped on the sides. The mule team was giddy, so I'd expect them by dinner.

JD said that Wanda wanted to have a stay in a Lawton motel for tonight. The best in town, hot tub and sorta a vacation.

She will be surprised to find that our best motel has bathtubs with feet and the hot tub part comes from Miss Kitty downstairs in the bar coming up every now and then with a boiling pan of water and a spatula..

Such is life in Lawton.

And you thought you guys were rural.

I did some other stuff with the MM files, but I can't post them on the board. Thales marketing guys would have a heart attack.

I will let JD know about them though.

I'm getting ready to post a few eval shots from last night. Pretty interesting stuff.

Deral Paulk, PLS OK

Some are bracing for Charlie tonight..I'm bracing for the Kilgore contingency.. Heck..Looking forward to it.. Sorry you couldn't come up also with your wife...

I read your email pertaining to the MM results from a couple days ago. It could be that the MM is the 'every tool' I've been waiting for Thales/Ashtech to come up with for several years now. Seems they may have done it (albeit accidentally). Oh well, intentions don't mean near as much as results, and getting out of the box from time to time will certainly give results.

jsb

By the way did you note the shift from the ITRF-NAD83 I posted below? Pretty interesting.

Now they are calling our 'new' unit the MM Classic..

I own cars that are classic. That implies stuff that is pretty old, but I'm taking it more as the MM Basic.

The MMCE has a new processor, and probably some other enhancments to the standard MM. Maybe better shielding to avoid reciever bias and a better antenna design..

I'll let JD in on the secrets I've found in the MM, but I will not post them on the board...

I'm thinking Thales is saying...I thought these guys were just rednecks..How did a redneck who went to OSU to get an ME decide to go into surveying and buy our stuff..lol

And yes..I noted the shift pattern from ITRF..Still researching it now. Gotta read all the stuff from Frank Moon that I printed out last month. A very good discussion on the main board about WAAS. Mainly him and me.

Deral

Do you remember a discussion with Mr. Geodesist on this subject when the WAAS was new? You will find it on this message board if you dig deep. At the time the phrasing was an irritation but the science project that Mr. G. set before me proved very rewarding to me personally. Several folks will get honorable mention in the next sentence but I want to thank Mr. G here again for his patience and straight answers to my questions. With some help from Frank, Mr. G, Dave Doyle, and some other very nice folks at the FAA and NGA I have learned a bunch about the WAAS, WGS84, ITRF00, and NAD83(CORS96).

There are a few things I can help with. The FAA went with ITRF00 because that is as close as the NGS can get to WGS84. The ITRF00 is as close an approximation of WGS84 as any of us will get. The reason for using WGS84 for the WAAS is because of a treaty requirement as I understand it. Why is not nearly as important as a comprehension of what it means to our measurements.

You can read more about the WAAS on the FAA web page at

http://gps.faa.gov/Programs/WAAS/waas.htm

I get a newsletter from the FAA once in a while that is very interesting.

The NAD83(CORS96) or HARN positions are shifted from the ITRF00 by amounts that vary across the continent. You can find out how much at each CORS station just by downloading the coordinate lists for the CORS from the web page at

http://www.ngs.noaa.gov/CORS/coordinates/

The NGS has software called HTDP that is used by some folks to compute the difference between the NAD83 and WGS84 positions of points. The software is a challenge but it is priced right.

http://www.ngs.noaa.gov/PC_PROD/pc_prod.shtml

I have submitted a feature request for the coordinate conversion between the ITRF00 and NAD83(CORS96) to be included in the tools. As the hardware reaches a point where the difference is not buried in the noise I keep hoping that the software will be made to handle the conversion.

I think we have reached that state where it does matter.

Bias no matter how small, if known, should be removed.

Deral

This, like some other things that remain a burr under my saddle, could be changed in more than one way.

Instead of expecting the GPS makers to deal with the bias why can't we all pester the FAA to use NAD83(CORS96) as the basis for their coordinates. For the purposes of landing on a runway what is two meters anyway? Yes, it would add some bias in a difficult landing but what datum and coordinate system is being used to map the runway?

Why does using NAD83 for the WAAS matter?

1. By executive order NAD83 is the national standard for mapping in the USA.

2. NGS data sheets are referenced to NAD83.

3. The state plane coordinate systems are defined relative to NAD83.

4. Elevations in the USA are referenced to NAVD88 and the Geiod03 model relates NAD83 to NAVD88.

But if it is time to change the world around a little then lets offer this alternative approach. Let's make the ITRF00 (aka WGS84) the national standard and get everybody to define state plane coordinates relative to the ITRF00. Then the WAAS corrections and the coordinate conversion software will all work just fine with existing software and GPS receiver operating systems.

For the purpose of differential corrections and post processing where we have control of the base station this is a non-issue. We put in the coordinates based on our personal preference for the desired datum and coordinate system. It only matters when we want to use the base station, like WAAS, that is owned by somebody else.

One alternative is to use their system. Then apply the corrections in our mapping software. As we prepare to load maps into the receiver they must me scoothed over to fit the broadcast corrections. When we download the maps from the receiver the maps have to be scootched over to fit the desired coordinate system.

This is a lot like the debate about how the GPS makers need to solve all problems related to local coordinate systems. My suggestion is that the CAD, COGO, and GIS software makers should provide tools that let the data base stay tied to the National Spatial Reference System while bearings and distances are related to whatever system we want. The benefits of such a system are much better than hammer fitting good GPS measurements to a lousy tangent plane map.

Now that we have a national digital elevation model and a well defined national datum to use as a reference framework the software tools needed for the various CAD, COGO, and GIS software products "should be easy to do".

But those are just the opinions of a dirt surveyor and map maker.

Yes.

Yes..

Heck yes..

Talk to your dad tomorrow. Wanda and him are staying tonight.

All was a resounding success (even the secret stuff worked)...

Deral

The ladies stayed with us throughout the day and watched with amusement every time we had a high five for a successful experiment.

I thought we might have a bit of fun and let them in on the game. My MM has our streets, sewer,water,survey control and section corners built as a background map.


I handed the unit to the ladies and pointed at a dot on the screen and asked them to go find it. The only instructions issed was that "the top of the screen is always pointing north"..

They took off, while JD and I followed behing listening to them and sipping some cold frosty beverages.

After a few blocks, then they declared they were at the dot. Gale has no survey experience, but Wanda has been around JD long enough to pick up quite a bit. She looked around and then down at her feet and found one of our control monuments..She asked if this was the little dot on the screen? Of course the bottom of the screen showed 25-01 (survey control number) and that is what was stamped on the monument, thus verifying the find.

I pointed out another dot (different symbol) and then they took off again. We nearly had to jog to keep up with them this time. They were having as much fun as us.. When they got close to the prey (this time a fire hydrant), they had already figured it out and practically ran to it.

The point.. They had never seen the MM or background maps such as these and within a few minutes could use it to find the points. If they knew what the symbols meant, then it would have been even quicker.

I'm thinking about the volunteer firefighters, water repair guys and other non-surveyors who only need to find some infrastructure for maintenance.

Oh..And we had baked potatoes (in the coals), corn on the cob and filet mignon on the charcoal grill....You missed a pretty decent meal.

And hooking up the Thales correction antenna was a breeze, although it took quite a few cables, but it was nice to see the MM screen drop from WAAS and start showing DGPS.. I think it took us all of about 10 minutes to get it figured out and hooked up.

The real time corrections consistently showed the ITRF bias, and if accounted for then we were generally hovering around the 1 foot level to the known coordinate.

Deral

From A PM2 antenna? How so? I ask.

Or, do you actually have JD's Reliance antenna?

I have a few extra L1-DGPS antennas around, if you need one.

Paul in PA

We used his Thales correction antenna for the DGPS stuff.. We disabled the GPS portion and used both the MM internal and the PM2 as the source of standard GPS signals for our testing.

And we then used the Thales correction antenna for both the DGPS and the GPS..

Results were similar.

I didn't say the PM2 Antenna provided the DGPS..You misread my post or I didn't word it correctly. JD pays for the Thales corrections..That is what got us the DGPS..

A blue pack with about 6-8 pounds of stuff (two camcorder battery's)... I just knew the MM, JD knew his correction stuff..

Together, we batched it together in a New York Minute.

JD is not in an area served by the Beacons, but we are so I would expect a NavBeacon to provide similar results.

The experiment was to make sure the corrections would talk with the MM..They did just fine.

Deral..

If I were to buy a Mobile Mapper, can I just feed it an L1-DGPS signal or do I need a decoder(receiver) to reduce the DGPS signal to NMEA(or whatever the code thingy) format?

Next question, will the MM work with DGPS corrections from 2 different DGPS stations simultaneously?

I've seen Garmin DGPS adaptors pretty cheap and CSI has a reasonable unit. Is there one in the Thales mix?

Deral, Using mulitple antennas with all those cables and signal joiners/separators is OK for a science project. Phil, will there be a production hardware solution down the road?

Paul in PA
Modified By Lawrence Paul Lopresti on 8/15/2004 at 3:18 PM

I guess I don't fully understand your question.

We were receiving via RTCM the corrections. Many sources such as the Omnistar, NavBeacons and the Thales Corrections supply this but you must consider the references frame.

We just had to tell the MM what baud rate and which type of corrections to look for and then if supplied it applied them.

The RTCM corrections are code corrections and not L1 corrections. A simple shift in dX,dY,dH... Nothing to do with L1.. It will not provide a fixed solution real time, but a fixed position based on the RTCM correction difference.

I think Thales already has a beacon solution based on their product releases. If you are in range of a NavBeacon source. JD is not, so we were using the Thales corrections (ITRF)..

Since the DGPS is a code correction, then there is no advantage to using two code corrections. I think it will only use one.. The closest one is preferably in most cases.

It is not like the ORGI in any sense.

We are not processing L1 data and doing a fixed solution. We are gettting a position then applying the shift from a reference station (Omni-Nav-ect.) to derive a position.


As far as this weekend. Then Thales said it should work, and we just proved it does work.. Nothing better than proving stuff in the dirt.

Deral

If I misread your questions, then elaborate a bit more..Thanks

There is an advantage to using 2 code corrections. As there is some variabbility in corrections as it is for the specific DGPS station location. You can get 2 different corrections from your 2 nearest DGPS sites. By meaning them out you can generally get closer to the possible truth. However at a specific location the coreection may be very near to correct from one station and way far off for the second. But at least then you are only halfway off the truth and can generally feel that you are closer to the truth.

There are some units that monitor 2 DGPS stations continuously. You can set them to mean out, or use your preference or the stronger signal as base and the second signal as a check. It lets you know if the second solution is beyond whatever tolerance you set for variation. This is real time.

I am taking it you need a receiver(decoder) to put the DGPS signal in the appropriate output format. Too many acronyms to keep them all straight.

Paul in PA
Modified By Lawrence Paul Lopresti on 8/15/2004 at 5:26 PM

The corrections using RTCM are based on code solution, at least on our end.

PPM's come into play at this point, so all things being equal then the closest station will provide the best results.

Meaning stations with a code fix will not improve a solution..I am positive that it will degrade your solition..

Again...RTCM is not like an L1 solution..
Deral
Modified By Deral_ Paulk on 8/15/2004 at 5:32 PM

There are three Coast Guard DGPS signals I could pick up. 60-100 miles away. NW, S & SE. It makes a difference to me.

The closest station physically may not be the station with the closest atmospheric conditions to my location. Similar conditions matters more than the distance.

It is a real time L1 solution, so everything and then some that can booger up your L1 solution is in play.

When I get 2 differnt locations from 2 different corrections I am going to mean them. I want the best from the data I have.

If not then I've just wasted $50,000 bucks for a college education.

Paul in PA

The DGPS beacons are fixing their position, but they do not transmit the carrier code to you, as you would need to do a L1 fixed solution.

The DGPS corrections are either the raw range errors for each SV or the error in position (dXdYdH). You cannot do an L1 fix from a beacon.


You are not getting any iono corrections from the station, so this point is moot.

With DGPS, I've used stations 200 miles aways and still gotten submeter results. There is no way that I would have attempted an L1 fix.

Deral in Ok