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360-Degree Prisms
Posted by davidgstoll on August 13, 2014 at 2:49 pmOK, there’s this type:
And then there’s this type:
So is there any difference in angular accuracy, both horizontal and vertical, between the two?
Dave
johnhls replied 9 years, 8 months ago 12 Members · 23 Replies- 23 Replies
The one on the bottom of your post looks like a knock-off of a GRZ4. The Leica GRZ4 original has a molded arrow painted yellow that should be pointing at the gun to increase angular accuracy. The more expensive GRZ121 is high accuracy (and high cost) when shot from any angle and I believe there is a mini version of it. You can get the specs from Leica sites.
Coady,
Both pics are Chinese knock-offs on eBay. They are both roughly $200, and probably the quality is in line with price.
Not having any experience with the GRZ4, I didn’t know about the Yellow Arrow. I’ll go to the Leica site and scope things out.
Thank you.
Dave
You know, I might be wrong about angular accuracy when using the pointer – it’s probably the distance that’s off (sorry about that) I waited too long to edit the post. There were some posts in the past regarding the accuracy of the Leica knock-offs – one of them was from a poster named Conrad. I have the GRZ-4 but haven’t even used it yet.
With the GRZ4 the yellow arrows will allow the user to align the sight of the measurement to what I call a “strong face”. On the GRZ4 the cost is lower because the corner cubes are not cut precisely to align the center of the cubes when you rotate the prism and look at the center of the cubes. If you just measure to the prism at a random face with the GRZ4 the specification is +/- 5 mm. However if you have a measurement that needs maximum accuracy with the GRZ4. You align on of the yellow arrows to point back towards the prism (person running the rood sees yellow arrow pointing back to instrument) the accuracy spec changes to +/- 2 mm whic is the same for the GRZ122 (more expensive). You just manually have to pay attention to the facing of the GRZ4 for tight shots.
The GRZ122 is more expensive because the corner cubes are cut so that the centers align “perfectly”. So no matter how the GRZ122 is facing the specification is +/- 2 mm. The GRZ122 also has the 5/8 thread mount on top for attaching the GPS RTK antennae.
Both GRZ4 and GRZ122 have the same dimensions.
There is a GRZ101 which is the mini 360 prism. It is only 30 mm tall and is great for close work. It has a specification of 1.5 mm +/-. It does not have the range of the large 360 prisms due to smaller reflective surface area.
There is allot of good information on the standards and contruction of the Leica prisms and other accessories at:
http://accessories.leica-geosystems.com/en/index.htm
Some good white papers if you are interested.
> So is there any difference in angular accuracy, both horizontal and vertical, between the two?
Don’t know about either of those prisms, but I’ve been robotic for about 20 yrs. I think you’ll find a major difference in elevation at close shots. Plus they won’t even take a measurement within about 5 ft.
When in doubt about the vertical, just shoot it again with an inverted scope. I think you’ll see a difference at close range (within 100 ft or so), but not so much the further out you go.
I’ve always had Trimble stuff, and they have their own quirks. It locks on the diode and not the prism, and they are a couple tenths apart. I believe it’s the same difference between the EDM and the scope. Advantage is it won’t lock on your reflectorized vest, a stop sign, parked car, etc. Just the rod.
Never worked with a 360 prism with a conventional total station, just the normal kind but you still have to make sure on the offset.
Thanks, Mark. Reading this one right now:
http://accessories.leica-geosystems.com/downloads123/zz/accessory/accessories/white-tech-paper/White%20Paper%20Surveying%20Reflectors_en.pdfDave
> Advantage is it won’t lock on your reflectorized vest, a stop sign, parked car, etc. Just the rod.
The last gun I used was the S6 and it dam sure would lock on all that stuff you mentioned – plus taillight lenses, licenses plates on moving cars, rear-view mirrors, etc. We had the first prism shown above.
I always laughed when it started tracking stuff going by on the road. I said it was “chasing cars”.
Actually, I don’t recall it ever locking my mesh yellow/lime green vest. It did seem to prefer the solid orange vest the other feller had on. I only remember that happening once or twice anyhow.Wayne,
“When in doubt about the vertical, just shoot it again with an inverted scope.”
That takes the error out of the gun, but the error in the prism would remain.
My inquiry into this prism thing started when I talked to a friend of mine who is laying out bolt centers with an S6 that is set up on top of a hill next to the project. He was concerned about using the 360-degree prism, and found that the measured location of the bolt changed if he rotated the prism pole. Scary. Myself, I haven’t used a fully-robotic gun yet, but it’s only a matter of time.
Dave
I believe those have different offsets, so there are some other considerations:
> My inquiry into this prism thing started when I talked to a friend of mine who is laying out bolt centers with an S6 that is set up on top of a hill next to the project. He was concerned about using the 360-degree prism, and found that the measured location of the bolt changed if he rotated the prism pole. Scary. Myself, I haven’t used a fully-robotic gun yet, but it’s only a matter of time.
Gosh Dave, I’d be scared too. I suspect an offset setting or an out of whack level bubble somewhere if it’s doing that. Could be time for a trip to Monsen Eng in Vegas and have things checked out.
I’ve never had a distance issue, but have seen vertical oddball stuff at close range. I use a 5600, which does lock on the diode and won’t shoot anything else. Never used an S6 and just assumed Trimble kept that technology. Guess not based on other comments.
Suggest to your pal to go reflectorless?? Just an idea. Or I can lend you my 40 yr old K & E and steel tape, but I’d have to look for my plumb bob… 😉
But radial staking anchor bolts is almost more scary.
PS – heard you guys were getting hammered with monsoon madness over there. It’s been circling around the mountains here, so just enough to make my truck dirty and the weeds get bigger. Stay dry.
Wayne,
My buddy is in California. I’m thinking of joining him, because Vegas is still fairly dead.
The level vial on the pole is the first thing he checked. It’s OK. But I’ve heard that even minor rotations of the 360-degree prism can affect the horizontal angle reading on a robot.
We got a lovely T-storm last night, and water ran in the gulches. Everything smells so good after a rain.
Dave
Thanks, Dan. Good stuff.
Dave
Just an FYI, Monsen Eng is a surveying equipment supplier and not an engineering firm. They are based in Salt Lake City, with a significant office in Vegas. I also believe they have something in Reno, as well as somewhere in CO. Not sure about CA, but doubt it.
Trimble is funny in that they do require exclusive dealerships that offer full service, and these guys do pretty well. I’ve spent lots of denaro there over the past several years and they are pretty good. The plus to me is LV is only 100 miles away and the Trimble guys in Phoenix are 200 miles.
I’m not promoting them or anything and have no vested interest. The proximity and service worked in my favor, that’s all. Talk to Bill there, he’s a good guy.
Good luck in CA. Assuming you’re an RLS here you should check the laws before you jump in head first, as they are pretty strict. Track down Ric Moore on this site, as he is the “go to guy” about things there. It’s almost a different planet….
> > My inquiry into this prism thing started when I talked to a friend of mine who is laying out bolt centers with an S6 that is set up on top of a hill next to the project. He was concerned about using the 360-degree prism, and found that the measured location of the bolt changed if he rotated the prism pole. Scary. Myself, I haven’t used a fully-robotic gun yet, but it’s only a matter of time.
>
> Gosh Dave, I’d be scared too. I suspect an offset setting or an out of whack level bubble somewhere if it’s doing that. Could be time for a trip to Monsen Eng in Vegas and have things checked out.
>
> I’ve never had a distance issue, but have seen vertical oddball stuff at close range. I use a 5600, which does lock on the diode and won’t shoot anything else. Never used an S6 and just assumed Trimble kept that technology. Guess not based on other comments.
>
> Suggest to your pal to go reflectorless?? Just an idea. Or I can lend you my 40 yr old K & E and steel tape, but I’d have to look for my plumb bob… 😉
>
> But radial staking anchor bolts is almost more scary.
>
> PS – heard you guys were getting hammered with monsoon madness over there. It’s been circling around the mountains here, so just enough to make my truck dirty and the weeds get bigger. Stay dry.can you elaborate? i do this all the time never an issue……some jobs i cant see any other way….but i like to learn!
I can verify that the top one is very sensative to which way each prism faces.
Remember, it locks on one prism, not an average. So, as you twist it the prism tracked changes. Both the distance and the angle will fluctuate. Also, all of issues inherent with zero offset prisms are present.
-All thoughts my own, except my typos and when I am wrong.Dmyhill,
Thanks. It looks like the 360-degree prisms aren’t as magical as I first thought.
Dave
You are better off using mini prism for precise layout, in robotic mode or not.
If you come across some money, Having 3-4 of those 360 prisms is pretty nice for construction jobs where resection is the main orientation/setup method.
James,
“If you come across some money…”
Money? What’s that? :-S
Setting 3-4 prisms over control points is a pretty good idea when you have to use frequent resections during the course of a day.
Dave
i guess that depends which instrument your using. the focus30 that i have tracks the center no matter what. it will aim right at the plastic between prisms if one prism isnt facing directly at the total station. i have tested it by rotating it aswell at 300′ and only changes around 1mm.
Is the Focus30 basically the same gun as the 5600-Series? I swear I remember reading something a while back (possibly on here) that pointing to a 360 prism was originally an issue with the early model 5600s, but that after a while they fixed it with a firmware update.
The reason I ask: I ran a 5600 for years and never had a pointing issue using a 360 prism, and even tried testing it a few times. I was a little surprised after we purchased a S6 to see that pointing with the MT1000 was an issue. I assumed that if they could handle it with the old technology they would have it figured out in the new tech as well.
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