For deformation work I like to use -30 mm offset prisms, and i have a bunch of them. I also have two 0 mm offset 360° prisms and one Trimble +2 mm 360°, but I don't like to use these for anything precise due to aiming issues. But, we do a lot of setups, and you always have to go back and turn the prism to face the gun at the new setup.
A neat product would be a remote controlled motor that could be used to change the direction that a prism is pointing. maybe a little light on top to aid in pointing it back to the gun.
Anything like that exist? Wouldn't be terribly hard to make...a small motor and a remote controller with a radio link. Be even better if it was integrated into the data collector.
In the late 70's, a guy that had worked for me, designed, built and used the remote prism concept. He spent a lot of time trying to get them patented, but the end result of this was apparently it conflicted with some other patent pending item. It may have been the developing of the remote EDM operating system or that they took his idea and instead of revolving prisms, changed the concept to the instrument instead. Needless to say, his idea never really got off the ground as far as being a commercially viable enterprise. He had written a program for his TI59 to do all his reductions to go along with using his setup in the field.
For those jobs that the traverse will be closed the same day I begin, my first backsite will be one fixed prism assembly on bottom and stack another target and prism on top with each facing different hubs.
Leica mini 360 has very little pointing error and is probably cheaper than a motor arrangement?
Do you have a part number for the Leica version (GRZ101?)? What I have is a large Zeiss 360 and a large Seco 360. I can definitely see the effects of misalignment (my EDM is 1 mm ± 1 ppm).
Lasse Kivioja did research at Purdue on the effects of misalignment of the prism on the distances, and created a very interesting report
Yes that's the one - GRZ101. they specify 1mm error, I think that includes pointing error and the other centring errors you may get when mounting it on a point.
Coincidentally I just had an email from SECO 1 hour ago about this new product you may be interested in.
http://surveying.com/Products/New-Products/6603-03
You will still have pointing errors unless you can view it from the same angles each time, but it does give you a couple of choices without having to move it.
Thanks for the report I will digest it at leisure...
ps you would need to be aware of the limitations of this prism.
I can search and lock on it up to about 100m away with Trimble S6.
The Leica "powersearch" does not work with this prism.
That email from seco is what got me to thinking...
I wonder if that 1.5 mm "pointing accuracy" is just that-meaning it can determine the horizontal angle to that accuracy. If you read Kivioja's report you will see the reason for the extra path length, and that it is minimized for offsets in the -30 mm range. So I suspect that there is still some effect from misalignment, although it is definitely different than the 360° prisms that I have. They are actually a number of small prisms set around a circle. So, sometimes you may be looking directly at one and other times you might be shooting in between.
Little by little I see optical tooling gizmos and field surveying gizmos converging. Sort of like the scanner sphere/retro reflector posting above ...
I actually built a working prototype for my own use years ago. I was able to cobble together RC parts and house it into a 4inch diameter PVC fitting with some machined aluminum parts top and bottom. Worked very well although the range was around 1000 ft and I thought that was not long enough to be a commercial success. Kept it around for years but did not use it in the field.
I have been using two of the CST Berger -30mm offset prisms stacked for sometime. Chris and I often work together on jobs running two robots, and use the same backsight on occassion.
Old thread I know, but I recently thought about this, was googling keywords/phrases and saw this thread as one of my top results.
Here is a link to what looks like the patent for such a device. Perhaps even by the person Charles mentioned, as the patent shows the Inventor was from Cheyenne, WY. Granted in 1983 and I would guess it had a term of 20 years, but I am not a PTO expert. It's kind of interesting to see the old sketches/figures there... and wonder why this doesn't exist. :unamused:
I am quite sure that a servo, 2.4GHz radio, LEDs (for alignment), small capacity Li-Ion battery, and optical plummet (plus an Hm reference mark if Trimble were to build it) could be constructed to fit into a standard "puck" diameter housing less than 100mm tall that could be used to rotate a typical prism (62mm) horizontally. From what I comprehend, this type of setup would be inherently more accurate than any 360?ø prism (that exists today), provided the placement tolerance of the servo on the rotational axis was appropriately minimized. As for vertical tilt, that would likely have to come as a purpose built kit, but the cost-benefit ratio on that probably wouldn't be worth it.
I guess I will just keep dreaming.
