Leica Robotic Prism: GRZ4 or GRZ101?

I suggest giving the existing prism a try for a week, just never found it noticable as far as weight was concerned.

the GRZ101 is a great prism for use in setting out - but it only goes on the smaller poles that have the smaller screw stubs :

http://www.surveyequipment.com/accessories/detail-poles/leica-gls115-mini-reflector-pole-4-section-screw-together?zenid=ib1aof5jpbp953lq12vjf9c0b1

(not the usual prism adaptor) so you couldn't use it with a standard detail pole.

I also found the ATR to be pretty rubbish at picking it out when setting out. I would usually end up using the 'joystick' to point the instrument in the right place again!

Hope that helps!

Tim

> I also found the ATR to be pretty rubbish at picking it out when setting out. I would usually end up using the 'joystick' to point the instrument in the right place again!

Do you mean that the gun doesn't track it very well as you move about, but when it finds it the pointing is good? Leica claims that the GRZ101 offers the highest pointing accuracy due to its small size.

Note that there's a quick-release adapter for the GRZ101 that allows it to be used on standard Leica poles:

Cool, I wasn't aware of that! We were only using it for setting out, so sticking it on a large pole wasn't required!

Once its tracking, its fine - but if it looses lock power search would struggle to find it. Hence the manual pointing to find it again!

I only really used it within say 50m of the instrument, so in theory the further away the better it should track!

Tim

We have the larger Leica 360 prism & would gladly trade it for just about any other non-360 prism. Powersearch had a hard time finding it in the woods, or at distances closer than 100 feet (the individual prisms that combine to make 360 degrees do not reflect enough of the search beam). I can only imagine that the tiny 360 would be worse (for Powersearch). Probably is more precise with ATR than the larger one, though.

At closer ranges (200' or less) the larger one can give horizontal/vertical errors of up to 0.06' if you are using it with ATR. This is because the ATR centers on the brightest return, and unless you are aiming at the little arrow on the 360 by eye (ATR turned off), that is usually offset to one side or another from the plumb line. You might aim it carefully but the robot just looks for the brightest return. The effect drops out by the time you get to about 200 feet. After that apparently the two visible prisms blur into one bright image that is closer to the plumb line.

Recently I watched a crew for an afternoon to try to figure out where their extra 0.20' on every job was creeping in, and the only thing I could really see them doing that would add that was using a 360 prism for lots of 50' work points and traverse shots. If there is a systematic error adding that 0.06' uncertainty to every shot and you propagate it ... whee!
Definitely would not use one as the only prism in the truck.

All that said, sometimes I wish we had 2 of them, because you could put them on tripods a thousand feet apart and free station between them all day without ever re-aiming them.

I live and die by the accuracy of my Leica setup, specifically bought another large 360° prism for the tribrach just so I didn't have to add the error of prism constants to the equation, the more human error I can eliminate the better the final product. I regularly triangulate and trilaterate, as well as old fashioned taped measurements for redundancy. I can honestly say at no time have I ever had 0.06' of error in measurement with ATR. I have a consistent 0.006' that is inherent to the mechanical limitations of the equipment, and willingly concede in fast track mode that stretches out to 0.03', but I don't use anything but standard measurement mode unless I am topoing, and then I'm usually in lock and track mode.

You probably work at longer distances, so the centering error drops out. If every shot was longer than 200 feet then it's no problem. Most of my shots are 50-150 feet so I start to see it.

I work busy construction sites where getting more than 200' from the instrument is an invitation for disaster. Sure there are times when I can stretch it out, but most of my work is done up close as well.

Do you collimate your instruments regularly? I am using an older TCA 1103 and find most of the time I can just leave values where they are after collimation, am pretty sure last time it went to the shop they left it alone as well. The EDM board was replaced last summer.

I will add that my instrument goes from the tripod to the case to the truck and never gets carried any other way than in the box. When it was the boss's gun it was important, when it is mine it is critical.

I use the larger 360 prism with a 1200 TPS. I get great results and have the uptmost confidence in its accuracy.
As far as weight, I don't see a big deal about the minor savings between the 2 prisms. I use the Leica Al composite rod w/8' leveling bubble) and with the Leica DC and prism and bipod its still pretty light setup to carry around. I can't see changing to the smaller prism simply for the minor savings in weight. I doubt it would be noticeable.

> I can't see changing to the smaller prism simply for the minor savings in weight. I doubt it would be noticeable.

The GRZ4 weighs a little over 23 ounces. I can't find a weight listed for the GRZ101, but it looks to me that with the GAD103 quick-release adapter it could be close to a pound lighter. That would be a significant savings to me (and my left arm!), especially since it would come off the top of the rod.

I'd have to agree with the comments about the weight issue being negligible.
For myself, I used a three-section pole with a data collector so the +/- 1# of prism wasn't so much an issue. Good luck with the repair.

I do all those things, collimate, carry in box, say sorry, bring flowers. Treat the Swiss Miss right.

The errors I am talking about are all from using the ATR and the 360 at closer ranges.
The 0.06' is not EDM error, it is H&V angle error. If you are aiming at the 360 by eye then no problem. Switched to the regular cylindrical Leica prisms and suddenly everything worked (powersearch in woods, ATR up close) & closed tight.

If you are getting the 6 thousandths least read accuracy when tracking robotically with a 360, then there's something I need to learn from your settings or procedure!

There's another little Leica gotcha about the difference between Fast mode and Standard mode on the IR EDM (I do not know if this changed on the TPS1200+ models, that use the same laser for both prisms and reflectorless): If you take multiple same-face shots in Standard mode, the ATR will re-point for the every shot. If you do this in Fast mode the ATR will not re-point, so the angle stays the same and only the distance is re-shot. I figured this out looking at some sets shot BBBBFFFF with a handheld rod. The error ellipses were long and skinny and I had to ponder how the rodman could be so tight side-to-side and not so much fore and aft. Read the manual about EDM modes and mystery solved.

I never use tracking, always powersearch + ATR. The TPS1200 firmware disables tracking when you mount the GPS antenna to make it a Smart Station, but it works fine to use powersearch and other automation (change face, position in 3D to stake a point) although it does turn much more slowly to avoid stressing anything with the extra weight of the antenna.

> I'd have to agree with the comments about the weight issue being negligible.
> For myself, I used a three-section pole with a data collector so the +/- 1# of prism wasn't so much an issue.

You guys are probably bigger and stronger than I am. At 135 lbs soaking wet, a pound on the rod is a big deal to me over the course of a day's topo. I've spent many hours shaving ounces off my Geodimeter robotic pole arrangement, with noticeable effect.

> Good luck with the repair.

Thanks! I've heard many rumors about lack of repair parts for the 1100 series guns, so at this point I don't even know if repair is feasible. I should find out one way or the other in the coming week.

"You guys are probably bigger and stronger than I am. At 135 lbs soaking wet, a pound on the rod is a big deal to me over the course of a day's topo. I've spent many hours shaving ounces off my Geodimeter robotic pole arrangement, with noticeable effect."

LOL, No, for myself i'm just lazier. That sleek and futuristic silver Leica robotic pole is fairly cool but was always just a half foot short of being able to clear any fence or obstruction I wanted to shoot over. I just got tired of taking the walk for an extended pole.

> That sleek and futuristic silver Leica robotic pole is fairly cool but was always just a half foot short of being able to clear any fence or obstruction I wanted to shoot over.

Are you're referring to the SECO 5711-10?

At 8.3 feet it's generally tall enough for my day-to-day work, so I'm not concerned about the height. What did surprise me is that it's actually lighter -- by about 3 ounces -- than the SECO 5129-52 carbon fiber pole.

I do all those things, collimate, carry in box, say sorry, bring flowers. Treat the Swiss Miss right.

Love it. They are demanding wenches, ain't they?

I reread one of your other posts and realized one thing I do religiously is make sure the benchmark I made on the prism housing lines up with the rod when collecting a shot. When dialing in for stakeout or rough topo, no big deal, but when collecting a shot one of my OCD rituals is to may sure it lines up. This may be where the differences occur.

Jim the pole I was referring to was the Leica GLS11

I wish I had known of the SECO prism pole. I had no idea Leica had the Mini-360 prism either.

Jim,

I have all three flavors of Leica 360 prisms. Both the original GRZ4 and the updated GRZ122 a little on the heavy side with the GRZ4 weighing in at 23.4 oz and the GRZ122 at 23 oz on my mail scale. While I have never found this to be a problem on a standard Leica rod it does flop around on top of a 7.5m rod. As for the accuracy issues mentioned elsewhere in this thread, I have never seen any significant error using the glass. I have using them since they were introduced in 1997 (I that was the year) and have done an extensive amount of testing with them. The GRZ4 is more accurate horizontally when the arrows are pointed towards the instrument while the vertical is just the opposite. This accuracy bias is all but eliminated in the improved GRZ122. The centering accuracy of both is 2mm.

At one point a crew lost one of our GRZ4s and being the cheapskate I can be I replaced it with a GRZ101. I actually liked the idea that it was significantly lighter at 8.8 oz when weighed with the GAD103. It also has a better centering accuracy of 1.5mm and a reasonable range of 350 meters. The one downside is that while both ATR and Lock work great, power search will not find the damn thing. The funny thing is that I swear it did in a previous version of the firmware. This makes it a little hard to find when it is sitting comfortably on said 7.5m rod. Another side note is that while the prism itself is 15mm in diameter and 30mm high the GAD is nearly triple the diameter.

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.

> one thing I do religiously is make sure the benchmark I made on the prism housing lines up with the rod when collecting a shot.

By this do you mean that you always point the same prism face (of the six faces) toward the gun? Or do you mean that you point any one of the three faces that are indicated by arrows on the opposite side of the upper bumper? I would expect, given the cost of the GRZ4 and Leica's reputation for accuracy, that all six faces would be centered horizontally, and that the three marked faces would also align vertically. (I understand that the unmarked faces are set a bit lower -- anyone know how much? -- than the marked faces due to the prism construction.)