My prism is one of the first GRZ4's and did not have the yellow arrows. I took a paint stick and marked one of the faces so the 180° side facing the instrument was the optimum facet for accuracy. I just line it up with the rod, perpendicular to the bubble. Like I said, one of my OCD things, find doing the same thing every time leads to consistency within my own world.
On our jobsite, we have multiple contractors and a gremlin .05'wide and .03' tall in the control network. It depends on who you talk to as to where the problem lies, as long as I can keep my gremlin smaller than everyone else, it's all good. With that degree of consistent recording procedure, mine is about .028 wide and .011 tall, by last check. That is on a 100+ acre site.
Jim,
We have been seeing about 0.012' vertical variance from the faces with the arrow to the faces without the arrows.
Ed
Huh. That solves a mystery for me, how to finesse the 360. I will have to try it again.
When I was first learning to run the 1203, I traversed my tiny urban lot time after time, trying to get a decent closure. Turning angles to the 360, it seemed like the ATR was picking upper or lower prisms randomly, even when trying to shoot it straight on. It would close 1:2000 with the 360 but 1:50,000 with the full cylinder glass. It's hard enough to close well at short distances and the 360 didn't seem to be helping.
Also, at the time I did not know that ATR points within a few seconds of the center of the glass and then calculates the exact center based on the image that the ATR is seeing, and records that data. This can be spooky to see in the scope because it gives the impression that the robot is not aiming very precisely ... I have since learned to trust the ATR (when kept calibrated) because no matter what it looks like thru the scope, the least squares results over the years say it can aim better than I can by eye.
Anyway, that's how I got stubborn about avoiding the 360 prism.
Just a note from many years of using Leica robotics for precision layout.
I have never seen 0.06' in error in any Leica instrument/prism package. Very early on, we did see small errors creep in when we did not use a Leica prism.
We used have several GRZ4 prisms - their stated accuracy is 5mm and 2mm when pointed at side with yellow arrow. We have since finally updated all of our 360 prisms to the GRZ122 which is 2mm no matter where the gun points.
When doing precision layout, standard equipment is the GRZ122 on a Leica pole with bipod and GPR1 prims on tripod/tribarach backsights. Using this setup we have no problem maintaining a 1-5mm accuracy throught the entire life cycle of a project. All control is run with GPR1 prisms on tripods with closed loops.
We also have several GPH1P prisms that we use for very tight control (centering accuracy is 0.3mm). We have compared measurements made with these special prisms with the GRZ122 and found few little difference between the two.
Of course, every one of our Leica guns are factory calibrated every 3 months or as a project allows and tribrachs, rods, etc. are checked and adjusted on weekly basis.
We are starting a project in two weeks that will require 5,000 points to be set within 5mm of plan coordinates and I would trust nothing but a Leica setup to accomplish this.
If you are not seeing a normal accuracy within hundredths, then either your equipment is not calibrate properly or your need to change your procedures.
The 0.06' was years ago, when we were first learning the equipment. Switched to regular prisms and it went away. These days we get results similar to what you cite, i.e., right at the equipment spec. From this thread, it sounds like at the time, we missed the key point that you have to aim the 360, strange as that seems. Happy New Year!
It is counter-intuitive that you have to be concerned about pointing a 360 until you study the construction and realize that even the modern 360's are just several individual prisms joined together. When I received my Topcon 9003 and the A7 prism I made the mistake of reading the short manual that came with the prism. Here's a quote from it: "Ensure that one of the 6 prisms is facing directly towards the total station. As for the position facing towards the total station, refer to the 6 direction marks on the top and bottom of the prism body. If the prism is not facing towards the total station, a measuring error may be produced in proportion to its inclination." So my misconceptions about 360's were quickly resolved. I think that the only reason 360's came into use was to allow reliable tracking while moving about a site.
Exactly so. On topo, that tiny bit of error is inconsequential, just as taking a ground shot a foot closer or farther.
On tight control or stakeout consistency and redundant observations are our friends.
> The bottom line is that any of these prisms are great for topo and standard construction. If you are running control or need precision greater than 2mm then use a GPH1P, GPR1 or GMP101.
The GMP101 is appealing due to its size, weight and cost. Does it work with Power Search, or is it too small?
Doubt it. Powersearch really seems to need a full size prism to work reliably.
Does your 1100 have Powersearch? Seem to recall it was introduced on the 1200s.
Powersearch is in addition to ATR and Lock, and uses a different mechanism, a vertical fan laser that is mounted in the telescope body on the lower edge. Not coaxial with the scope like ATR/Lock.
> Does your 1100 have Powersearch? Seem to recall it was introduced on the 1200s.
It was available on the 1100-series, though I think it was introduced after the series had been out awhile. I think it was a response to complaints that the regular search was painfully slow. Mine has it, though I haven't had an opportunity to try it out yet.
