I'm going to be adding a 2nd crew to my operation soon and am currently engaged in working up a list of equipment to outfit it. While we do the lion's share of our work with a total station shot lengths rarely approach 1000'.?ÿ I am wanting to have 2 prisms (in addition to a 360) for use when running control. I'm thinking that mini-prisms will be sufficient, take up less room in the truck, and cost less.?ÿ ?ÿ
But will they negatively impact accuracy? What say you? And what kind of practical range could I expect with one of them and a Trimble S5, for example?
Mini prisms are great for close work and setting monuments.
They are difficult to see at a distance and to get a shot on thru any kind of foilage.
I much prefer looking for and at a regular sized prism with a target for anything over 100ft and expecially into the trees and into shadows.
The accuracy is the same with either.
BTW, a second crew will usually cost twice as much as the first crew, it puts you into a whole new bracket when all the costs are put into place.
good luck
The last time I took all my prisms to a calibrated base line the mini prisms turned out to be the most accurate: the?ÿ worst, 8mm in 1,475 meters.
If you set the prism constant offset for each prism, any prism should give essentially the same accuracy as another over most of the working range.?ÿ
Error will increase if you are stretching the range so the return signal is weak or too close so the EDM is oversaturated.?ÿ
The limitation on accuracy should be centering error and temperature & pressure settings.
Mr. OK
I went to all mini (Leica) years ago and have never looked back.?ÿ Just shot 311m with ATR to one today, no problem.?ÿ If you were turning to them conventionally the size might make it harder to see but if you use the magic of robotics then that just is not an issue.?ÿ They are cheaper, lighter and smaller and according to Leica, just as accurate as the circular.
I'm a big fan of the Leica GMP101.?ÿ Small, light, accurate and I routinely get over 1,000' robotically.?ÿ On the one I use the most I cut off the portion of the target that sticks out beyond the frame in order to allow me to get the prism closer to building corners and the like.
I'm curious if you've had any tracking problems to the gmp101 in wet conditions? ?ÿThe prism in use didn't have the rubber hood they supply them with but not sure that would have kept much rain off.
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Demo'd a Zoom90 and while traversing a shower came through, enough for small drops on prism and I got some 0.04m tracking errors using atr on a couple of shots. Backsight was 250m, foresight 200m. Was doing the traverse in three separate jobs hence I could prove tracking error. ?ÿNot seen that sort of issue with the standard gph/got circular ones.
I like to have the full size for running control, for distance, but mainly poor conditions, fog, dust etc.
Sure do hate being able to see the glass but not shoot until the fog burns off.
I do, but removing the plate changes the offset, and I want all my minis to have the same 17.5mm offset.
Check a little closer, the housing is offset to accommodate the plate, removing it will not change the offset.
Check a little closer, the housing is offset to accommodate the plate, removing it will not change the offset.
I stand corrected.?ÿ I certainly removed the plate to saw it off, and I find it hard to believe that I was so inobservant as not to see the step in the housing, but the only thing I can figure now (about 9 years after the fact) is that I wanted the bottom part of the plate in place to make adjusting the prism angle with my thumb easier.
but the only thing I can figure now (about 9 years after the fact) is that I wanted the bottom part of the plate in place to make adjusting the prism angle with my thumb easier.
I'll buy that 😉 ?ÿ
Licensed Land Surveyor
Finger Lakes Region, Upstate New York
Soooo...... Following up.
I took delivery of a Trimble S5 last week and bought a pair of Leica GMP101 mini-prisms, from Allen Precision, to use with it. They arrived last week and are extremely nice.?ÿ I also bought 5/8" thread to bayonet mount adaptors. Slick.?ÿ We used them for the first time on a site survey yesterday and something new, to me, came up.?ÿ
The prisms are clearly marked as having a +17.5mm offset. Turns out that is valid only if using them with a Leica instrument?ÿ (or, presumably, any of the several Leica derivatives). With any other brand you must subtract 34.4mm from whatever Leica has written. So this +17.5mm is actually a -16.9mm offset when used with my Trimble, or with my old Topcon.?ÿ
Conversely, when using non Leica branded prisms with a Leica instrument you must add 34.4mm to the rated offset.?ÿ?ÿ
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Got a shot at 1500' with a mini-prism not too long back.
Always beware when mixing gear from different sources. With the (very) old Kern rectangular prisms, used with a Geodimeter the constant was different depending upon which way up you had the prism ( on each axis - hence 4 constants!). We still have a couple we use occasionally on the back of the inflatable -no great financal hit if they ever fall off into the water. For that purpose a few cm. on the distance doesn't matter.
