Are 360 prisms height to center normally off? I??ve noticed pretty much every 360 prism I??ve had has been .01??-.03?? off when I measure height to center. Current one is consistently .03?? lower than measured height to center. If I use the regular flat prism it??s unusual to be more than +/- .01?? when I back-sight the previous setup. It does well with horizontal usually at .003??-.005? on the distance and dead 0 on the angle. Just curious if this is usual for 360 prisms?
I asked about this from Leica few years ago.
The triangle shaped mirror "centers" on Leica type 360 prisms (GRZ4, MPR122 etc.) are offeset from prism center and this is intended. Its +-2mm on GRZ4 and +-1mm on MPR122.
The reason for this is because its impossible to manufacture such a prism so that the triangle centers on each side?ÿ would intersect at exact?ÿ same height. For this to happen the prism wouldnt have any diameter because you would have to "bend" the triangle mirrors up/down and they would collide at 0.
Use other prism types for accurate height measuring or fix with prism height depending if your shooting the upward or downward mirror.
Very hard to explain, hope you got the point...
I did not notice this issue with my Leica grz4 prism. I always pointed the yellow arrow toward the robot and error seemed reasonable.?ÿ
It's slightly worse on the Trimble multi track I use now but not what you're seeing.?ÿ
Take a shot using?ÿ leica circular prism?ÿ on your pole?ÿ then change it with your 360 prism aligning one face at the time with the instrument. Compare the elevations. My 360 reads the same elevation when the face tilted upwards is towards the instrument on farly flat ground , the face tilted downwards?ÿ reads -5mm.
@350rocketmike The yellow arrors sides are to be used to maintain good elevation, the ofther 3 faces would generate an elevation difference of close to 0.02'.
Probably a good time to post this paper again:
Leica and Trimble are slightly different, but both are within 3-4mm vertically no matter how it is rotated. Leica tends to have the edge horizontally by a mm or two, but Trimble is locked down tight in the vertical as long as you are using semi-active or passive mode.
95% of the graphs show deviation less than 3mm, or 0.01ft. If I need better than that I'm going to a miniprism way down low, or digital levels.