That's a common belief among non-Surveyors ...
Nebraska doesn't have the number of trees that most states have, but I did overhear a land surveyor once say that that they could get the RTK shot if they fixed out in the open and then quickly ran into the trees to get the shot before it unfixed. To each his own...
I wrote my MS thesis on gps under canopy. Give me your email and I'll send you a copy if you're interested.
It's entirely possible in a science-project sort of way. It really comes down to whether it is repeatable or not.
I was able to get repeatable survey grade results under heavy doug fir canopy. It was not efficient, and was not something you would stake from without a lot of post-processing and checking.
I wrote it up on the old Board so it might still be there, but here's what it took:
mission planning: perhaps most important. set your planner for a 25 degree horizon, then pick the times where the GDOP is less than 4. This gets you a roughly 45 minute window twice a day. Plan your day around it and be there set up and logging beforehand. You can always use TEQC or something to trim the data.
recording rate: 1s at bases and rovers. Also very important.
multiple bases: I used the WSRN bases and sometimes a Virtual Rinex with a very short baseline. (Sometimes this was the only thing that was both fixed and repeatable).
multiple occupations: otherwise how do you know it's repeatable?
I used a dual frequency receiver, will try the same method again with an L1 soon.
So yes, it will work, under limited circumstances and with many caveats. I did it on a few points that I couldn't brush or chainsaw and that I could not have efficiently traversed to.
The Boss scrutinized it thoroughly, and accepted it because it was repeatable AND it matched some modern traverse data by a tenth. Not saying you SHOULD do this, only that you can, and YMMV.
Dude! send me one too!
AS said above... we use a combination of GPS to set control pairs and a ground traverse between them them if we are staking a line, boundary, etc under canopy but we do recover existing corner monumentation under canopy using Static GPS techniques...and the thicker it is the longer the observation time...and you can be pretty confident after processing as you have control over your precision during the process. Multiple vectors from additional receivers is a plus.
These new BLK III satellites that start going up in 2014 will have a stronger signal and are predicted to penetrate dense foilage and they are talking a usable constellation of 70, 80, or 90 satellites when intergrated with GPS systems from other nations. Couple that with advanced antenna technology from the receiver manufacturers and who knows. Until then keep the Agent Orange on hand and nearby.
> I wrote my MS thesis on gps under canopy. Give me your email and I'll send you a copy if you're interested.
Oooo ooooo.... (waving hand franticly) .... send me a copy too. 😀 Please.
Larry P
That's a common belief among non-Surveyors ...
LOL ... I had a Sokkia Salesman tell me the same thing about 10 years ago ... but I knew better at the time ...
Me too please!:-)
That's a common belief among non-Surveyors ...
You got that right. I was waiting for you to chime in. I would like to put on an all day seminar at Myrtle Beach State Park. You think we could come up with one? I would like to run a conventional traverse with total station with all but a couple of points under canopy. Let me know what you think. It would probably generate some good data for comparison.
Brooks
It was a good read.
It was a good read, and confirms in a much more formal way what we have experienced.
We have taken shots under canopy and then traversed in to check the shots. They have never been good enough; and were off in the same ranges you report. Hopefully time, more satellites, and better antennas will make it possible.
Thanks for sharing your paper.
Stealth technology
One of the hands remarked the other day that if they could cover an airplane with cedar branches they'd have the best "stealth" ever. No radio signals can ever get through them..
Yeppers, that sounds like a good read, include a copy to my mailbox too....
I saw this post this morning and figured he would get the replies he did...be nice is trees were not an issue, thats when a person really needs it..
I am in Search and Rescue and one of our members sends me links to interesting things...here is one on GPS indoors????
Interesting. I've always wondered if it were possible to make ground based transmitters that work like GPS on wooded sites. Like you set 3 or 4 transmitters up on control points around your site, then you could walk the site with a rover, getting your position from the ground stations. It would likely only be good for X,Y, though ... no elevations.
