L1/CORS TEST #3
Posted By J.D. Billings on 12/8/2001 at 9:48 PM

The results are now in for the third weekly examination of positioning a single Locus unit (screwed on a POST) from 5 "nearest" CORS stations. I'll recap with all the previous coordinates to date, and end with Test #3 coord's.

Original Coordinates Derived "Locally"

N 6835851.505
E 3100685.732
ELE 402.979


Test 1 01.325 0600-1400 UTC

N 6835851.427
E 3100685.739
ELE 402.873


Test 2 01.333 0700-1500 UTC

N 6835851.422
E 3100685.757
ELE 402.956


Test 3 01.340 0600-1400 UTC

N 6835851.415
E 3100685.742
ELE 402.728

Looks like the vertical may be floating a bit, but considering these positions were determined from CORS stations at 65 miles, 124 miles, 124 miles, 124 miles and 181 miles, I'd think a 0.15' spread in the observation sessions is fairly decent. I don't think I could run conventional surveying from those distances with that kind of repeatability.

Hopefully the "Final Exam" will be done in the next couple of weeks....... Positioning with a dual frequency unit on my precious POST to process to both the same 5 CORS stations and send to OPUS. Maybe then with results from those two dual frequency sessions I will have some "benchmark" coordinates acceptable to the "majority" to use for comparison and analysis of the L1 results.

This little experiment in no way quells my desire to possess dual frequency units. Can't help but 'spearment with all this technology though. After all, I'm the one that blew the electrical breakers for the entire South wing of Chandler Elementry School in 1963 with a failed "science project". (Wasn't really a failure...I just eliminated one possibility).

Hope you're not all bored with my experiment.

J.D. Stumpwater R&D, OPIE LITE Division



PPM....
Posted By Mike Margolis on 12/8/2001 at 10:20 PM

remember Locus is spec'd vertically at 10mm + 2ppm, that means 2mm per km of baseline length.

Average baseline of 125 miles is about 165km x 2ppm = about 330mm (roughly a foot) of allowable vertical error.

I think the fact that you're within 0.15' at ten times the distance that single frequency receivers are designed to be used at is nothing short of incredible.

Thanks for the effort, personally I find your experiment very interesting.


Re: L1/CORS TEST #3
Posted By J.D. Billings on 12/9/2001 at 12:30 AM

Thanks Mike

I find Ashtech receivers, and especially Ashtech Solutions Software to be "nothing short of incredible". Well, the software anyway. I'd suppose any survey grade L1 receiver could be capable of these results, but I'm not sure about the processing capabilities of other softwares. At least as far as ease of use as I have to consider myself an uneducated novice in the general field of gps.

I still have to cling to my original theory here in that the amazing results are in some way attributable to the geometry of the constraint network and the ability of the processor/least squares adjustment to force the error uncertainties to the "middle".

I'm really looking forward to the L1/L2 CORS and OPUS coordinates for comparison. Then on to the joint project between the Stumpwater, Texas POST and the Coon Ass Kitchen Station somewhere in the marsh land of Southwest Louisana.

J.D.

Mike, any tips on how to evaluate these extremely long base line networks would be appreciated. The 95% error estimates on the adjusted position of the one unknown point (POST) were between 0.087 and 0.117 N, 0.111 and 0.144 E, 0.122 and 0.170 Ele, in all three tests. That in itself looks like a fairly good indicator. Do you agree?



JD...Were certainly not bored...
Posted By Trimble Man on 12/9/2001 at 6:51 PM

Still trying to work through the math on the Trimble processor and find out why I had such a bias...Was hoping that Kent could shed some light on this fact...
I believe our difference may be located in the software, but don't think that is necessarily bad...None of my software says that we should be doing what we are doing... (of course, if your like me, then you press the envelope every day with equipment)...

Still perplexed (so what's new) in Oklahoma..

TM


Re: JD, amazing stuff!
Posted By Brian Ewing, PLS on 12/10/2001 at 12:27 PM

JD,

Pretty damned good results for L1 during a peak cycle of solar activity! I doubt if you're boring anyone with these experiments (certainly not me).

Good luck,
Brian


Very quick post...
Posted By Trimble Man on 12/10/2001 at 6:34 PM

Have redone the data (and in violation of Trimble's practice)...Did not seed any coordinates...Came very close to your results...Hmmm....What does this mean, if anything?
Probably doesn't mean anything, since they (Trimble) are assuming that I am not trying to process L1 at over 100 miles...

Still working on it...

TM