you can target the target, not the prism so that even if the prism is not aimed precisely at the TS, the sight is good.
The angle will be good when aiming at the target, but with zero offset the distance will be very slightly off when the prism isn't aimed at the instrument.?ÿ That is the purpose of the -30 mm offset - for the ~3 inch prisms that offset makes the distance measurement insensitive to aiming.
I recall seeing a sketch someone here did (well over a year ago), that did that math, and if I recall it correctly, the error fell well below the standard error for a typical 3 or 5 second instrument (constant plus proportional parts); nearly an order of magnitude below, making it inconsequential to the analysis. I think the assumption was something like a typical pointing error of +/- 5 degrees or so (for the prism).
Your statement that the -30mm offset makes the distance measurement insensitive to aiming, but surely the same can not be said for the angle measurement, could it?
I think the assumption was something like a typical pointing error of +/- 5 degrees or so (for the prism).
Your statement that the -30mm offset makes the distance measurement insensitive to aiming, but surely the same can not be said for the angle measurement, could it?
I'd think 5 degrees would require some care in pointing with just the guide on a prism, and a lot of work might be done with larger prism pointing errors.?ÿ
Wouldn't you always aim a manual TS at the target, which is centered over the point??ÿ Then the angle would be right and the distance would be measured with the beam slightly off the prism center, but still close enough to work, even if the prism was aimed many degrees from the instrument.
On a robot, I'm not familiar with their aiming algorithms to know what effect the prism pointing would have.
you can target the target, not the prism so that even if the prism is not aimed precisely at the TS, the sight is good.
The angle will be good when aiming at the target, but with zero offset the distance will be very slightly off when the prism isn't aimed at the instrument.?ÿ That is the purpose of the -30 mm offset - for the ~3 inch prisms that offset makes the distance measurement insensitive to aiming.
I've tested this with my CST prisms and targets, and it's not the case.?ÿ Both angle and distance are good even when turning off-line.
I think the assumption was something like a typical pointing error of +/- 5 degrees or so (for the prism).
Your statement that the -30mm offset makes the distance measurement insensitive to aiming, but surely the same can not be said for the angle measurement, could it?
I'd think 5 degrees would require some care in pointing with just the guide on a prism, and a lot of work might be done with larger prism pointing errors.?ÿ
Wouldn't you always aim a manual TS at the target, which is centered over the point??ÿ Then the angle would be right and the distance would be measured with the beam slightly off the prism center, but still close enough to work, even if the prism was aimed many degrees from the instrument.
?ÿ
Aiming the prism with the built in sight, you can get much much closer than that. I'd be surprised if I'm ever more than 30' out at 250-500'.?ÿ
The point I was trying to make was that, aiming at the target with a 0 degree offset prism that is aimed improperly would result in an inconsequential distance error.
