Prisms for staking out

If I am doing general layout even at 5mm, i use the mini 360 prism as the tracking is decent and doesn't drive me nuts. However for things with tight tolerances or when verticals are important, I will use the nodal prisms like you use GMP111-0 for setting out.

which mini 360 prism are you using Sireath?

i use both the Leica GRZ101 or the sokkia atp1s. The advantage of the sokkia is that it is a sliding prism so you can adjust the height on the fly.

I use GRZ4 on 2-5 foot pole.?ÿ 5mm but 2mm if aimed at correct face.?ÿ Good all around prism I use for everything I have to do. And my mm are more accurate than yours:)

Is the positional accuracy of these 360 mini prisms okay when low to the ground?

I know with my Trimble MT1000 that if its too high or too low compared to the robot the positional accuracy is diminished.

@fobos8

Just for those folks that can offer help, but are unfamiliar with metric.

Fobos is actually staking to 0.016 ft accuracy.

I use a Topcon GPT9003 Robotic with a A7360 prism or a ATP1 prism for staking out.

I started out with a Topcon/Sokkia -30 offset prism but found maintaining prism lock was a problem so I went to the 360 prisms.

I do have some problems with accuracy in critical stakeout work such as concrete nails in concrete and punch marks on cast-in plates for steel columns for building construction.

I am on my knees with a 1 foot pole.

I find check measurements can be different by up to 5 or 6mm (1/4")

I am also looking at testing instrument settings with fine and course measurements.

I compare fine 1mm with coarse 1mm settings with quicker update repeat measurements but looser specs for the coarse settings.

fine 1mm is +/- (2mm +2 ppm) for measurement time of 1.2 sec and coarse 1mm is +/_ (7mm + 2ppm) for 0.5 secs

so coarse does not look good

I had a hire PS103 with RC5 and magnet field recently and had similar problems.

I was able to eliminate the problem with a fine rapid measurement setting for bluetooth TS connection but the problem was still apparent with the RC5 connection.

?ÿ

?ÿ

Do the red neck check. Set the whole rig up, 11 feet apart, with 2 tripods, and as near to the same elev at both ends. Shoot dist. Check with box tape.

It's fast, easy, and de-intellectualizes the whole process. You might want to use several different box tapes, to "get picky".

N

Some interesting reading in a paper by a Queensland (Aus)?ÿ student surveyor 2011 Matthew McDonald

https://eprints.usq.edu.au/22560/1/McDonald_2011.pdf

I don't believe that 360 prisms are as good as they're rated for. set one in a tribrach and rotate it while measuring continuous, watch your values change. for highest accuracy, round prism is necessary. also, lock on a mini 360 is hard to maintain over about 40m and forget about wide search. this is with MS60

@loganwoolf

Every 360 prism I've encountered is designed to be most accurate when turned so that one of the faces/individual prisms is facing directly to the instrument.  Just like a traditional prism, turning them off angle will result in errors unless it is a nodal prism.

@loganwoolf

ironically the grz101 works better with trimble instruments! because their passive lock is much less fussy it will search and lock much easier. Leica powersearch does not work with these. A Leica MPR122 or a Topcon ATP2 are examples of slightly more compact 360 prisms that will work with powersearch.

the down side is that they are easily distracted by reflective material so for my sites I lost patience with it and moved to active lock exclusively. Using leica instruments now though.

We are using a minus 30mm peanut on a carbon fiber gps pole for line stake out in the woods (height doesn't matter). The S6 doesn't stick to it as well, likes reflective vest almost as much. Like it because no weight and same offset as BS and FS. It could be 2 tenths off and no one would know or care. The existing line hacks are up to 5' off, probably run in with compass 30 years ago.

@dave-karoly

It is becoming rare to find hack marks along boundaries.

A lot of paint splattered within 20ft of line is very common.

Many new fences off that much when there is an old downed fence along the boundary.

Not many people asking for hacking and painting boundaries because of the price.

We usually set new tpost along boundaries and a big yellow machine clears it out and some keep that area mowed and others fence.

@dave-karoly

Trimble would do well to bring out an active mini prism. Something like the old 5600 (RMT??) prism would be a good start.

At one point I did look at experimenting with making an LED that would flash in the correct manner and start that way. Though I never made any progress before I ended up moving back to Leica equipment.