"Fixed" should not necessarily be considered synonymous with "good" or "correct" especially in bad locations. More time would improve the result. In an area like that I would try 20 minutes.
Post pics of difficult shots
- Thread starter Matthew D. Sibole
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You may have to set there for a long time, how long, I am not real sure there are any set rules for how long to occupy when in canopy, just experience. My preference would be to check it again later too. A PPK solution can come back as a float solution. Fix is statistical, not neccesarily meaning it is a correct solution.
It is good to test the limits like you are doing with your equipment. Thats how you learn.
Wes Cole
Active Member
Yeah I understand "fixed" is statistical and not necessarily "correct", I've seen bad fixes. In this instance it was experimental.
When I go back to review the plat I may set back up and let it run for 20-30 minutes just to see what I kind of results I get...
There's motive behind my testing and questions. I have about 1.8 miles of boundary to survey in a very mountainous area. I would like to use the LS on the front end to recon the line and get some close shots when/if we recover the corners. Then we will have to traverse the line with a total station, our contract requires it. But I believe the use of the LS on the front end will save a ton of time keeping our traverse online as we'll have to come back and sign/paint/blaze the lines.
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Darren Clemons
Well-Known Member
The LS will get correct and very accurate data in coverage such as this - at times. Other times it won't and will require as Adam and others have said at least 10 minutes of PPK. I learned the hard way also testing like you've done and had several PPK solutions come back "fixed" but not be correct using the five minute minimum, so I've upped my "line in the sand" as Adam called it to 15 minutes in heavy canopy.
We have had our LS totally underneath pine trees, up against the trunk of up to 24" trees and it's amazing what it will do. Just have to be, as we all are, very careful and check, double check, and then triple check.
I've seen spots like you show underneath the beech tree where it will sit for 15 to 20 minutes and do nothing. Come back to that same spot an hour later or maybe the next day and - bang. It may get it in a matter of minutes.
So many factors like wind blowing the leaves, where and how the constellations are and even cloudy thick skies seem to make a difference.
One thing I've started doing quite a bit with this LS, I think it might've been Jim Campi who first mentioned it, is to rotate the LS in a different direction to try a little different alignment.
However, if I do this, as long as the unit is on a bi-pod, and stays plumb, would/could it affect my PPK raw data that I'm collecting by moving it just a titch?
Wes Cole
Active Member
Darren, very good info!
I believe that if I took that same observation under that beech in mid December I'd not only gotten good PPK values I'd probably gotten good RTK values too.
The time duration is the learning curve on the LS for me.
Hope no one takes my post as a knock against the LS/T1M, the fact that it got within 2 feet of the real value under that tree is still IMPRESSIVE! I believe the Javad systems are the best on the market, wouldn't have bought one otherwise!
DPOS is processing using phase center variations now so the receivers should be aligned to north (T-2 and T-1M record button and green triangles to the north, LS display to the north with the compass reading 180 degrees). Processing with phase center variations mostly improves the vertical results. A good paper about this topic is Influence of GPS antenna phase center variation on precise positioning.
No one thinks that Wes, as a matter of fact the feedback from all of us users is why, Javad is so much ahead of any other GNSS equipment manufactures. I have learned probably more from this forum, than any dealer or salesman or support techs combined. It is interesting how Javad Users get on this forum and help each other figure out things, it's a community in my opinion.
Nate The Surveyor
Well-Known Member
Spot on.
Nate The Surveyor
Well-Known Member
Dixieland delight!
Darren Clemons
Well-Known Member
Javad, the nature friendly GPS
Darren Clemons
Well-Known Member
When I got to this point I was sure I'd have to stay and get at least 2 separate 15 minutes dpos sessions.
I had the first validated RTK in SIX minutes! Stored that shot and started another and intentionally let it run for 15 minutes to get a dpos, which I base processed after getting back to the office within 0.017!! from the RTK shot!!
The most amazing of it all was a good portion of the phase two collections were with 6 full engines.
How did the 1st post-processed shot compare to its RTK solution? Did the 2nd shot get a RTK solution?
Darren Clemons
Well-Known Member
I didn't even post process anything on the first shot as I already knew it was good in the field. The 2nd shot also stored a validated RTK within 0.04' of the 1st shot. I also had a good survey line I was following and had an inverse from the other end of that line within 0.08' after the 1st shot so I was confident it was good right off the bat.
I only did the 15 minutes PPK just so I'd have a dpos to compare out of curiosity on a point this tough.
Just so hard to understand what/when it will do things like this. Look at my interference numbers - very high.
Also, this is within a mile of a spot I was at last week when I couldn't get it to shoot anything
like what we've become accustomed to (spoiled is a better word).
Of course, we had tons of rain last week. Lots of wet leaves and honestly, it seems to never work this well on overcast, cloudy days.
I only did the 15 minutes PPK just so I'd have a dpos to compare out of curiosity on a point this tough.
Just so hard to understand what/when it will do things like this. Look at my interference numbers - very high.
Also, this is within a mile of a spot I was at last week when I couldn't get it to shoot anything
like what we've become accustomed to (spoiled is a better word
). Of course, we had tons of rain last week. Lots of wet leaves and honestly, it seems to never work this well on overcast, cloudy days.
It is hard to say sometimes. Most of the time I am amazed with where I can go reliably. Sometimes I'm disappointed. I see that picture, Darren, and it looks like any given Tuesday for me. Generally, if I have to wait for thirty minutes to get that shot (like you said, two DPOS solutions) it's worth the time compared to conventional traverse for one man. So when I can get them in 5 minutes, it's a bonus. I agree that wet leaves make it much harder to get a verified position in canopy like that, but I haven't really noticed any problems on cloudy days vs. uncloudy days. I did have a job this week that was all total station. Too many pine trees to use GPS. I tried, but it just wasn't going to happen. So far I get about 80% of my work done with the Triumph-LS (boundary surveying mostly), and I find myself in places like you show in your picture frequently.
Good for you getting that kind of redundancy on those points. Javad gives you enough on the front end to know you have a good point, but the surveyor in me likes to see redundancy.
Good for you getting that kind of redundancy on those points. Javad gives you enough on the front end to know you have a good point, but the surveyor in me likes to see redundancy.
I don't have the pics, they would not do it justice anyway. I topod 2 acres on the North slope of a piece of property close to table rock, NC on Table Rock Mountain Rd. I had planned on doing it with the total station but when I got there it was nasty thick, probably 10 year cut over and steep steep. I used the LS and a 12 ft pole. I was able to crawl thru it all and topo the entire site with the LS. I will post a Google earth of it later. I would have spent two days cutting for optical topo.
Darren Clemons
Well-Known Member
The main reason it's so frustrating sometimes is like I said, this LS has completely spoiled me! It gets points like this in six minutes and regularly, reliably, goes where like they say in Star Trek "where no GPS surveyor has gone before" so when I have days like last week - lots of what I'd call marginal canopy - and I have to do 15 minutes after 15 minutes to process dpos, I think something is wrong.
Is is like you say, any given Tuesday, it seems. There are so, so many things that affect canopy RTK: base position, radio strength, elevation drop, wet leaves, radio interference, heck even solar flares. It was so odd last week I looked online to see if there'd been any major events. There wasn't.
Many, many times you can be struggling on a spot, walk away for 30 minutes and go back and bam - it'll eat it right up. Problem is, I'm usually to stubborn to walk away for a while or it's the very back point two miles from the truck!
Fact of the matter is, I wouldn't even be in half these places trying RTK with any other GPS system out there!
I agree. I was serious about that 80% figure. The LS is reliable enough that when you get to that 20% that's a no-go, it can be frustrating for sure.