Gps, when used under canopy MUST have redundancy. And, must have a mechanism in place to quantify tolerances. Ie, 0.03' 0.05' 0.07' 0.10' 0.15' etc.
I have given a bit of thought, on how to compare gps systems, under canopy.
The closest to reality, and reasonably fast, should get a higher score.
Items that have meant alot to me, are
1.) Real life conditions.
We are often trecking into crazy locations, with search areas that are 3' to 50' in diameter. So, if our equipment gives us bad data, we would not know it (by comparing to previous data). I've SEEN work by my competitors, that had 3' errors, in 60 feet. That is, 2 monuments, that were shown on his plat as 60.00' apart, and, I found them at 62.87' apart. I know he uses rtk. This is pure equipment abuse. It's happening right now. While I'm typing this. This is due to a lack of redundancy, and a lack of a mechanism to quantify tolerances.
With rtk surveying equipment, you MUST have redundancy. And a mechanism to quantify tolerances.
So, my motivation to discuss this, comes from a noble sentiment, towards our profession. And, a desire to see my colleagues make informed choices, on what tools, for what job. And, to eleminate abuse of tools.
2.) Simplicity of use.
We are surveyors. In so doing, we have to learn stuff. New ways, to do old things. We need equipment that does not require a doctors degree to operate.
-zz-
So, here is how I suggest to test them.
Index the poles bubbles first. (lets eleminate this error source!)
Set groups of nails, (dimples in top) down through the woods. A group is about a foot apart apiece. (so that they have similar environment, and obstructions) Each is a different color. Set as many nails, as contestants/gps units to test.
Contestants are given instructions.
Pick a color, and occupy it until you are comfortable, that you have sufficient data/redundancy, for a boundary survey coord.
There are 10 groups of nails.
Start the timer, and go!
See who gets through all 10 groups, the fastest. (only occupy one nail per group).
Afterwards, shoot all nails, with total station.
Also, 2 nails, out in the open, to localize, or index on.
After everyone has run through the "gauntlet", upload the total station data, and all the gps shots. (different layers).
Publish the data.
So, each gps user gets a time through the gauntlet. And an accuracy, on each point. Ie, difference between total station coord, and gps coord.
The final results, could be reduced to:
Time through gauntlet.
Total error, (add up all inverses, gps to total sta data)
Any outliers.
This could give the end users a better working knowledge of the tools we use.
As an addendum, this test could be repeated, 24 hrs later, (plus, or minus a couple of minutes). If, somebody got left out of the test, and wanted to compare another brand.
I'd like to know the results of this test.
I'm sure somebody has a better way to do this... But that's an idea... And maybe a start.
Of surveyors being more informed and in charge of our profession.
What do you think? Got a better idea?
Let's talk about it. I don't work for any company. I just promote thoughts.
Of course "what we bought is the best". It's brand bias. (IF there was something better, I'd have bought it...) goes the thinking.
And, i can tell you this. If i could get Javad performance, out of one of those tiny sokias,
That'd be interesting...
N
Nate,
Your test through the "gauntlet" would have to be performed over several days to provide an answer to the question being asked.
During testing of an unmentioned feature, on an unmentioned brand, it became abundantly clear to me that the only way to perform such comparison testing is to use an antenna signal splitter, and a single antenna. The "truism" of real estate is "location, location, location". It holds true for comparing receivers in a high multipath environment. The fact that you can not physically place two receivers in the same location means that there is no "exact" way to compare them. It would always leave questions also if we were using external antennas for such testing. I have proven to myself that two identical receivers w/internal antenna, sitting side by side can have radically different performance in the woods. The only difference being location. Swap them back and forth with quick connect adapters, just to find that it is the location that is more favorable, not the receiver.
In other words, it would take anywhere from one hour, to several days to declare a winner in your test.
To provide real world testing stress regarding "time through the gauntlet". The penalty for a bad submitted coordinate is loss of license, or the life of your neighbors dog. That should discourage the drive by rtk shots.
Nate The Surveyor, post: 428132, member: 291 wrote: Gps, when used under canopy MUST have redundancy. And, must have a mechanism in place to quantify tolerances. Ie, 0.03' 0.05' 0.07' 0.10' 0.15' etc.
I have given a bit of thought, on how to compare gps systems, under canopy.
The closest to reality, and reasonably fast, should get a higher score.
Okay, I realize that you are Javad's director of Research and Development for the Ozarks, but what put you off the obvious idea of actually *surveying* the test points to determine their positions to check various on-the-run methods against?
Too much variability, Nate, having the different tracks. It would be almost impossible without a lot of redundancy to determine if performance differences were due to the receiver or the minor differences in multipath near a particular point. Using ground marks, like nails, you also include potential sources of error in the pole and bubbles that may make the apparent measurement errors seem worse than they are.
John's idea is better, but it takes out of the equation the actual antenna of the RTK rover. So you would only be comparing receivers and receiver engines and not the entire RTK rover (which should include the GNSS antenna for the rover).
I think the best way to compare them is similar to what [USER=1087]@Mark Silver[/USER] does. Have two stable mounts (quick connect preferable), located about 1-3 feet apart. Set receiver A on mount 1 and receiver B on mount 2. Collect a point on each. Then swap and repeat, then swap back again and repeat and continue. While neither receiver will be on the same point at exactly the same time, the repetitive process should allow each receiver to experience good and bad observation times meaning out biases. This should be repeated over the course of hours.
This process only compares two receivers at a time.
I believe you could also do this with a single mount by mounting receiver A on the mount on Monday and repeating multiple shots on the mount throughout the day then set receiver B on the mount on Tuesday during the same time and perform the same test, then put receiver A back on the mount on Wednesday and then receiver B on the mount on Thursday, etc.
If you had several mounts you could test as many receivers as you have mounts (ie mounts 1, 2 and 3 and receivers A, B and C). Each day the receivers would advance to the next mount. On day one, receiver A on mount 1, receiver B on mount 2, receiver C on mount three, on day two, receiver A on mount 2, receiver B on mount 3 and receiver C on mount 1, etc. I would repeat this such that each receiver hits each mount at least three times.
A careful total station traverse would be very helpful. I would look to use a base from the same manufacturer as the rover instead of using one base to provide corrections to all of the rovers. The bases should be in an optimum location and placed as near each other as possible, preferably on mounts rather than ground marks for the same reason as the rovers.
Nate I'd suggest these nails need to have legs and tribrachs set over them and used for comparisons to be somewhere fair.
One could argue otherwise, but at least it takes out pole, bubble issues. (assuming tribrachs are accurate)
I'd also suggest a TS station out in the clear, where "just about any GPS (don't get too excited about that phrase) would get a fix.
A decent backsight, similar in clear and radiate each "under cover point". Fix with all test GPS and as John says do same over couple days through the day.
This surely would be interesting.
Issue I see is the difference between species of trees. What is good for one species, not so another.
And then time of day, frost, wet windy. Gets a bit complicated.
Maybe good to repeat all in another part of the country.
Richard, post: 428165, member: 833 wrote: I'd also suggest a TS station out in the clear, where "just about any GPS (don't get too excited about that phrase) would get a fix. A decent backsight, similar in clear and radiate each "under cover point".
Yeah, that's a pretty easy solution to actually determining the actual positions of the control points to be splattered with RTK shots. You don't need to be deep in the Arboreal Forest to be in a highly obstructed location due to tree canopies. In that same setting, moving 10m practically guarantees a completely different environment for GPS/GNSS positioning.
While your at it. let's test the tilt sensors on these devices.
Verify a location in open sky, free of multi path, with TS. Then set fix a 2m pole at a 15å¡. Occupy for same time duration with is each device in the test. Record length of time calibrate the IMU, Compass and sensor, and accuracy of located point.
Well, I dont have signal splitters... But I do have an old LegAnt Topcon antenna.
When my rover fell over, it broke the antenna. Lee Green sent me an extra. So, I have 2 good LegAnt antennas. And one broken one.
So, if anybody has a signal splitter, we could do this.
I know my LS can use an external antenna.
N
Any test under canopy will have to include some means of quantifying the canopy. The canopy one encounters in Oklahoma is much different from that in Oregon.
Gps, when used under canopy ..... you are not supposed to be there if you are surveyor.;). Yeah seems like another Javad glory wave.
OK, this thread keeps popping up every few months...
More and more surveys are getting done, with gps, under canopy, with inadequate redundancy, and causing havoc.
It bugs me.
N
Surveyors using GPS in "heavy canopy" sounds like a full time employment act to me. Keep on truckin!
I watched an owner of topcon hipers, go into canopy. Used float to get close, then got a fix, stored it, and used an inverse, suunto compass, and box tape, to set a '40 cor'.
Got no witness trees.
One fix. One corner.
Later, I retraced one of his surveys. He had a bust of 5-6 feet, in 1/4 mile. (bad distance between) And, a whole passle of lot corners, were set off of those 2 corners. I did not retrace those. But, it's happening. As we speak.
N
Nate The Surveyor, post: 428231, member: 291 wrote: I watched an owner of topcon hipers, go into canopy. Used float to get close, then got a fix, stored it, and used an inverse, suunto compass, and box tape, to set a '40 cor'.
Got no witness trees.
One fix. One corner.
Later, I retraced one of his surveys. He had a bust of 5-6 feet, in 1/4 mile. (bad distance between) And, a whole passle of lot corners, were set off of those 2 corners. I did not retrace those. But, it's happening. As we speak.
N
Bad techniques are not limited to any technology or manufacturer. What you saw was plain and simple bad surveying.
Mark Mayer, post: 428207, member: 424 wrote: Any test under canopy will have to include some means of quantifying the canopy. The canopy one encounters in Oklahoma is much different from that in Oregon.
Agreed because the canopy in East Texas is WAY different than in Central/South/North or West Texas.
