Yesterday we had to establish a couple of radiation stations, and due to circumstances, had to use this prism. The station was higher up and the shots to prism were maybe about 40 degree down. This prism is fixed and cannot be tilted as per normal traverse prism.
JUst wondering if anyone had verified that the measurements would not be affected by this lack of tilt ability for this particular prism or is it? TIA
About a week ago there was a thread titled "How much does prism selection affect Accuracy?". Check for it, and the very good video that the OP of that thread produced and linked. I've never seen that specific model of prism before, but it appears that it would have the same issues that the Trimble MT1000 multi-track prism has.
The short answer to your question is yes, there would be some adverse effect on zenith angles.
Interesting ..Thanks.
FWIW we were using Trimble Access and SX12 combo, and this particular prism is selectable inside the Access measure mode. One would think that Access is smart enough to 'compensate' for this oblique angle shots?
I wouldn't count on Access knowing any more than the prism constant. I've never seen anything written (either in manufacture' literature or elsewhere) about software correcting for high angle observations.
With any shot on a high angle I default to a tilting, and nodal, reflector. That being said we were using the same Trimble 360 last year a magnetically mounted to structural steel modules when setting them and it seemed to work well (though we were doing our localizing observations at a similar angle so there wasn't a default known value to compare to).
360 prisms are intended for moderate-precision topographic work. They'll maintain datasheet-level precision until you start going outside of 15-20 degrees vertical angle.
Trav kit / tilting prisms are what you want for establishing control that is significantly higher/lower than the current setup.
It would have been interesting to record the vertical angle manually and compare with the stored one.
How far was the distance btw? If I was in that situation and had doubts about the prism, I would have tried a reflectorless/DR shot to the top of the prism as a check for the slope distance then compare the two values.
