I have two of the above instruments (a 3" and a 1") and didn't realize until too late that although the instruments are specified to be of thia ponting accuracy, it does not apply when you use the "autolock" feature which was one of the main reasons they were purchased.
I have done a test in my office where I set up the S6 and also set up a tripod approximately 50' away. When you let the instrument lock onto the 360° mini prism or the larger trimble 360° multitrack prism and set the horizontal angle to 0°, and then rotate the target approximately 30°, the horizontal angle changes by approximately 32" of arc. While this may not seem like much iof you are using the instrument for stakeout routines, it does come into play if you are traversing. I have done some rough calculations and it seems that you have to be approximately 800 feet from the instrument to where this rotation will introduce only 1" of angular error which is what the instrument is spec'd to. I have also tried this with conventional prism (-30mm os) and there is also an unacceptable error introduced, although I have not documented it as well.
It seems that a resolution might be to use a prism that has a sighting scope on it so you can always point the prism at the target in the same manner. I don't have a prism that will accomplish this so am wondering if any others have encountered this problem and if they ahve come accross any resolution.
Thank you.
Maybe I'm confused as to what you're doing.
when you turn the prism on the tribrach, how do you know you are exactly plumb? Trying to get a handle on what you did and the results. Couldn't the 32 seconds be a combination of plumb line/prism error?
Sounds like you need a nodal point prism.
I don't traverse with the 360^ -
for control- we use precise tribach adapters and -30s- this resolves the issue. We also turn 4 sets.
On side ties with the 360^, we use -30s on the backsites and tie either from 2 backsites or from 2 different occupied points (preferred). minumum of 3 sets for the dc to dislpay residuals.
Adjust it all in Star*net.
Ditto, except that I use either a Leica TCRA1203 or a Leica TCRA1103plus. The 1103 just came out of the shop almost like new and it turns like new. The 1203 is in the shop right now. It has to go back to Leica to get the "you haven't calibrated recently" (although I have) message turned off which is goofy in my opinion. But despite the crazy Swiss backwards thinking software Leicas are the best mechanically and optically.
This is how we traverse with our S6's. I believe it even says somewhere in the Trimble documentation not to traverse with 360 prisms. Seems like pretty common sense.
This is one of the reasons I switched from a Geodimeter 640 robot to a Leica TCRA1102plus. With the Geodimeter I wasn't able to get repeatability of position better than about 0.03', and it was mostly due to direction rather distance. On small urban boundary projects that just isn't good enough. With the Leica, which I use with a Leica mini-prism (GMP-101) when I want to bear down on the errors, I'm nailing everything.
The Geodimeter tracks better, but the accuracy problem was a killer for me. I sleep better now. 🙂
> This is how we traverse with our S6's. I believe it even says somewhere in the Trimble documentation not to traverse with 360 prisms. Seems like pretty common sense.
I never heard that about the 360 prisms. We traversed and did everything with a 360. Only once we did we have to go back a re-shoot a couple of legs.
Our biggest problem was our S6 was it liked to "chase cars". i.e. license plates and brake lights. It also liked to lock on to signage and the reflective strips on our vests. Guess that's why I baby-sat the robot so much while the PC was having all the fun.
Yup, still does that in autolock mode. Not when using active track though.
The trimble traverse prisms have sighting pointers.
I'm not exactly sure what you're asking, and I use a 5600 instead of an S6, but I do know that while using Autolock, the pointing axes are offset. This is from my 5600 manual:
That figure is scary.
Nothing scary about it. This is referred to as autolock collimation, and is compensated for. The specifics ate detailed on the pages following the graphic that was posted.
This is not surprising. The instrument will aim at the nodal point of the glass (where the faces all intersect). If the nodal point is in front of the prism pole/tribrach centre, then rotating the prism will introduce an error.
We have a few methods to minimise this problem.
Traverse with circular prisms, preferably with the nodal point aligned with the centre of the tribrach/prism pole.
Ensure that the prism used can meet the requirements. eg: the GRZ4 has a pointing accuracy of 5mm. That's the difference you'll see if you shoot the two different faces. Only the one with the arrow marking is correct. Therefore, if we're doing work that requires more accuracy we don't use that prism. We use a mini360 (1.5mm pointing error), or the precision mini (<1mm pointing error) or a circular prism (<1mm pointing error) or the new 360 with 2mm pointing error.
Finally, if we use a 360 prism and want to be a bit more accuracy, then we shoot two faces, and turn the prism 180 degrees while the instrument changes face. This removes the issue of prism having a pointing error, the verticality of the prism pole and the instrument collimation.
I'm new here so please correct me if I have this wrong.
This thread seems to cover 3 or 4 different errors.
Having the S6 track left and right as you spin the 360 prism would not be a tracking error. The target, the nodal point of the prism, is moving from side to side, so this would be an issue with the position of the prism. This would also be an issue with vertical angles and I suspect the controller corrects for this (but not any horizontal) error when you use the 360 prism.
Is the "pointing error" that CSS refers to the worst possible result of the apparent offset between the pole axis and the nodal point of the prism?
CSS says "we shoot two faces, and turn the prism 180 degrees while the instrument changes face. This removes the issue of prism having a pointing error, the verticality of the prism pole and the instrument collimation." Seems to me that spinning the prism would do none of those things. To the ccontrary, the only thing you could expect is that, if the 360 has an odd number of prisms, then the target or nodal point will shift to one side or the other.
I have pasted this from another post I responded to last night..
I use an A7 360 prism and have had no trouble traversing with it..What I have discovered however, is when rotating the rod, the pointing will deviate slightly from center..so..I use the following technique to ensure best results...find and point the prism class in "near perfect" alignment to the instrument and the center pointing becomes quit perfect.
I first discovered this "non-perfect-pointing" of 360 prisms some time ago when we used older 360 "circular" prisms (not of the inverted triangular type) in conventional 'tracking' mode and while observing the rodman run the rod, I could see that the prism was not pointed directly at me resulting in 0.04'+/- (diameter of the rod) and when rotating the rod, pointing alignment became centered. Having experienced this..I observed the similar using the A7 360
You are absolutely correct! on the construction series instrument white pages the robotic accuracy is called out as 10mm. I find the same issue and even a greater issue with the multitrack prism. The way the gun tracks the prism is by equalized zones of the light the prism is producing. So four zones divided in the tracking recepticle. If the bottom row of the prism is covered Vertical can be off. If you are near an object of any type with the prism the light striking that object influences the tracking. If you do not believe me cup your hand over the prism so you cover the instruments view of the prism and the gun will track your shirt. if you have a vest with reflective tape you can have the instrument locked and shot a distance and will have an incorrect shot. I had safety stickers for the site I was working on on my hard hat and did an as build of 10,000-15,000 shots 10% were wrong.
Errors of 2"-3" were common. it cost me weeks of rework and embarressment. If the objects had not been at a standard distance apart I would have not realized the errors. I would have taken the equipment for calibration.
I have demostrated this to the local trimble representative and inquired three times regarding an answer for months. They will not reply or admit to the problem! This is the worst equipment on the market! I will never trust or purchase from them again!
> You are absolutely correct! 1.)on the construction series instrument white pages the robotic accuracy is called out as 10mm. I find the same issue and even a greater issue with the multitrack? prism. The way the gun tracks the prism is by equalized zones of the light the prism is producing. So four zones divided in the tracking recepticle. If the bottom row of the prism is covered Vertical can be off. 2.)If you are near an object of any type with the prism the light striking that object influences the tracking. If you do not believe me cup your hand over the prism so you cover the instruments view of the prism and 3.)the gun will track your shirt. if you have a vest with reflective tape you can have the instrument locked and shot a distance and will have an incorrect shot. I had safety stickers for the site I was working on on my hard hat and did an as build of 10,000-15,000 shots 10% were wrong.
> 4.)Errors of 2"-3" were common. it cost me weeks of rework and embarressment. If the objects had not been at a standard distance apart I would have not realized the errors. I would have taken the equipment for calibration.
>
> I have demostrated this to the local trimble representative and inquired three times regarding an answer for months. They will not reply or admit to the problem! This is the worst equipment on the market! I will never trust or purchase from them again!
1.) Can you post a source for this 10mm error? The S6 instrument spec. claims an RMSE 4mm + 2ppm (though I am unclear on the units of the ppm)
The observed error would be a function of distance, would it not?
I used the S6 with the Trimble 360 passive prism on a large project and never saw more than .05 on grade stake checks (yesterdays stakes) at 700' staking distances. I chalked it up to poor quality tripods/tribrachs and sloppy measure downs and pen strikes on stake markings.
2.) You are saying using the LED array, staking with the LED array half obscured, the S6 will aim at some place other than near the center of the prism nuggets?
Is this error horizontal or vertical, and how could there be much vertical error, since the instrument would fail to get a return unless it was pointing closely to the band of prism nuggets? From my experience MultiTrack and the S6 will not observe a distance unless it is also observing the LED emission. And my experience with the Passive 360 prism, is that it won't get a return unless it can see the nodal point on an individual nugget.
3.) This happens frequently when using a road-safety vest with the passive setting on the S6.
4.) 1 minute of angle equates to .03' of error at 100'.
The error of 3" would be .0015' at 100'.
This equates to .015' at 1000'
Where does this make a difference?
>spec. claims an RMSE 4mm + 2ppm (though I am unclear on the units of the ppm). The observed error would be a function of distance, would it not?
PPM stands for parts per million and is a dimensionless ratio.
At short distances the spec is 4 millimeters.
At 1000 meters the spec is
0.004 + 1000 * 2x10^(-6) = 0.006 meters
etcetera. That's how it depends on the distance.
It's statistical in that for 68% of the measurements with this kind of instrument the resulting error is somewhere between +/- that amount, more if the instrument drifts out of calibration over time.
He's saying 2 to 3 inches, not 2 to 3 seconds.