I have never liked the common tribrachs out there. The ones with the optical plummet in them. Sticking out like a sort thumb. For starters, it sticks out, and can get bumped.
Topcon made one LIKE this: http://www.ebay.com/itm/NEW-Topcon-Type-Single-Prism-Tribrach-Set-system-for-total-station-surveying-/141850507976?hash=item2106f2fac8:g:GjMAAOSwv-NWawY4
Anyway, WITH the rotating rig, it seems you can 100% check it, without a bit of trouble.
Just set it up, and rotate the rig 180å¡, and you have checked the rotation bubble, and you have also checked the plummet. From this, you can adjust the snake eye one. Also, it is NOT vulnerable to being bumped.
Now, having said that, others have said that the rotating part of some of these left some to be desired... I don't know.
Anyway, why did the rotating style, I linked to above, not get more... um use, or people that used them?
I'm just looking for answers....
N
That type of carrier, if it is a good quality one, is indeed more precise than the common tribrachs with built in optic plumb. But I suspect that the particular one in the linked ad is a chinese knock-off like the one my boss bought before I came to work for him. It's highest and best use is in the office, as a paper weight. Junk.
Check out the price of a good quality carrier here.
And a decent plumb-less tribrach here.
Save your $95. It's counterfeit, not even really a Topcon.
Given a quality Topcon plummet setup there is no question of the advantages. There is a second advantage in that it is relatively easy to get this setup rod height to match your instrument height, negating the requirement to have to re-measure when jumping tripods. Typically my instrument height measure 0.31' or 0.32' higher than the rod height when using multiple tripod setups.
That being said I bought a cheap one and was disappointed and have never used it except as a spacer when I need a slightly higher rod height on a tripod setup with an plummet tribrach. Another use would be under a GPS antenna on a tripod but I have 4 fixed height rods with tripeds and seldom set up a fifth receiver anymore.
Today the majority of my work is with prism poles and bipods or tripeds and a rod height of 5.00' One rod setup bottoms out at 5.00' the other slightly less. I keep promising myself to disassemble the pole and slip a rubber spacer in to bottom out at a 5.00' reading.
Paul in PA
Mine are Leitz & Sokkia (they all look identical except the name) with insert similar and looking like this and they are perfect for swapping out with the instrument when using tribrach with optical plumb and making one setup per hub for less than half the price and half the weight.
The name brand version of that was about $700+ per set.
Here is a nice vintage illuminated set topping the scales at 150lbs.
http://www.ebay.com/itm/360805582025?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
In my opinion, only non optical tribrachs with optical adaptors should be used... Benefits are so many over other tribrachs And its height should be the same height of total station. Problem is thay are not cheap. Or maybe to put it correctly, cheap should be avoided
Somewhere around here I have a couple of HP3820A tribrachs with optical plummet inserts and prism adapters. (I might have the targets, too; I don't remember.) HP borrowed the Kern concept of using a locking lever to secure the instrument or other insert, and it's not compatible with Leica-style 3-leg equipment, so I never used any of those tribrachs in the field. They well-made and pretty cool, though.
These are my favorite:
http://surveyequipment.com/leica-professional-precise-laser-plummet-traverse-kit/
optical are a touch more precise, but these are fast, easy, and very durable. If you're force centering the added error from the width of the laser is probably less than half a millimeter. If you're needing to do tighter work than that you should be doing resections with mini prisms, anyway.
I don't like the ones that stick out like a thumb, either. The Trimble optical traverse kit is pretty nice, but we seemed to have a lot of trouble with the precise level staying in adjustment on those.
I use a similar target from Sokkia as I am using Sokkia Robotic. The beauty is the ease of adjustment and calibration of the plummet and also at each station I can do a quick check to check the centering error.
A bonus is that the the centre of prism height is the same as the total station height
Plumb Bill, post: 397799, member: 226 wrote: These are my favorite:
http://surveyequipment.com/leica-professional-precise-laser-plummet-traverse-kit/
optical are a touch more precise, but these are fast, easy, and very durable. If you're force centering the added error from the width of the laser is probably less than half a millimeter. If you're needing to do tighter work than that you should be doing resections with mini prisms, anyway.
I don't like the ones that stick out like a thumb, either. The Trimble optical traverse kit is pretty nice, but we seemed to have a lot of trouble with the precise level staying in adjustment on those.
I am curious what is the error ellipse you get between resection with target prism and mini prisms? My assumptions was always target prisms were more accurate then mini prisms cause you can hold it steady and the pointed tip will be blunt and not as sharp as the optical crosshair
Nate The Surveyor, post: 397769, member: 291 wrote: I have never liked the common tribrachs out there. The ones with the optical plummet in them. Sticking out like a sort thumb.
they seem fine to me.
For starters, it sticks out, and can get bumped.
in my experience, nothing happens when they get bumped. ours stay in adjustment just fine with normal use.
Topcon made one LIKE this: http://www.ebay.com/itm/NEW-Topcon-Type-Single-Prism-Tribrach-Set-system-for-total-station-surveying-/141850507976?hash=item2106f2fac8:g:GjMAAOSwv-NWawY4
Anyway, WITH the rotating rig, it seems you can 100% check it, without a bit of trouble.
i can check and adjust our "common tribrachs" without a bit of trouble as long as I have a total station on hand. I settle at about 0.4mm or so centring accuracy but can do a bit better if i spend longer on it.
Now, having said that, others have said that the rotating part of some of these left some to be desired... I don't know.
i have tested 4 of the Wild GZR2 precision carriers, and they orbited a central point at about a 0.15mm radius or so when spun. If your prism carrier of choice is much worse in terms of rotation tightness than the Wild precision carriers then you are probably not much better of than what you can adjust a GDF322 to with its "common", built-in optical plummet.
Anyway, why did the rotating style, I linked to above, not get more... um use, or people that used them?
I'm just looking for answers....N
i don't prefer these topcon style carriers, but i have seen my fair share of them around. most people with topcon and trimble gear that i see use this kind of setup. what makes you think they aren't widely used?
Nate The Surveyor, post: 397769, member: 291 wrote: I have never liked the common tribrachs out there. The ones with the optical plummet in them. Sticking out like a sort thumb. For starters, it sticks out, and can get bumped.
Topcon made one LIKE this: http://www.ebay.com/itm/NEW-Topcon-Type-Single-Prism-Tribrach-Set-system-for-total-station-surveying-/141850507976?hash=item2106f2fac8:g:GjMAAOSwv-NWawY4Anyway, WITH the rotating rig, it seems you can 100% check it, without a bit of trouble.
Just set it up, and rotate the rig 180å¡, and you have checked the rotation bubble, and you have also checked the plummet. From this, you can adjust the snake eye one. Also, it is NOT vulnerable to being bumped.
Now, having said that, others have said that the rotating part of some of these left some to be desired... I don't know.
Anyway, why did the rotating style, I linked to above, not get more... um use, or people that used them?
I'm just looking for answers....N
First, Nate, you should know by now: There are no stupid questions.
I, too thought the built in optical plummet tribrachs were the thing to use, but couldn't find any on ebay reasonably enough, so settled instead on the "turret" type. Never looked back. I have one used Topcon, and one knock off (which I bought for much less than the $175 for the unit and shipping thing you found on ebay). Quite frankly, if babied somewhat, they stay in alignment about the same.
I discovered early on, the value of setting the height of the prism to the same as the instrument (I do a lot of "zero centering", multiple tripod setups).
But I gotta say....I thought that with that new fangled box on a stick you got, you didn't have much time for this here old timer's optical stuff.;)
My thinking is similar to Nate's so I invested about $100, including shipping, to try one of the cheapest rotating optical plummet adapters and the matching non-OP tribrach from China. I found that even after adjusting the bubble level to match my total station, the adapter still could never be adjusted so it would rotate tightly around a target point without the bubble moving off center. More importantly, I learned the reason why it was so cheap. The optics were not image erecting. With a normal optical plummet you move the tribrach in the direction you see it needs to go. With my particular cheap version, the image is reversed so you have to move in opposite direction to what you see. Needless to say that "feature" was not included in the advertising.
sireath, post: 397813, member: 9370 wrote: I am curious what is the error ellipse you get between resection with target prism and mini prisms? My assumptions was always target prisms were more accurate then mini prisms cause you can hold it steady and the pointed tip will be blunt and not as sharp as the optical crosshair
A good mini prism has replaceable tips, so that is not an issue. Also, they are a fixed height, adding another value towards precision.
I did an expirement with our mini prisms one rainy day: if I kept the bubble in the inner ring I would get consistent distances to .001', if I let the bubble go outside the ring, but still touch the ring I got distances consistent to .003'. Just a very brief indoor expirement trying to set different targets over the same point will show you that tripod and target setups are about .005' repeatable on average. You can do better, but setup takes forever and you have to watch adjustment t like a hawk.
We proved to ourselves many times over that we could do better work almost as if by accident with mini prisms.
Disclaimer: all bubbles aren't created equal, buy the good stuff.
Also, we were using a Trimble S6 HP model. The setups noted above are more an example of relative than absolute precision.
Guess I need to upgrade .... sigh.
I don't ever recall bumping the tribrach with the optical sight. Where I worked before we always used the topcon with the built-in optical sight as well as the see-through sight. I thought that was great. setting the instrument up over the tribrach (or one of those rotating rigs) you could spin it and check the plummet from all angles. You could use the simple setup for simple work and add the rotating rig for other work. Sounds like a good way of simplifying your work also if you can clip-in and get the same height as the instrument (if that can, indeed, be done).
For the most part, whenever we spun the instrument and adjusted level, we would seldom have to fine-adjust the instrument over the point.
Well, I do have that new fangled thing on a stick, and is says Javad....
However, I have circumstances, where I want to PRESERVE a point. This calls for the following protocol:
Set up a CORN tripod. This is a TALL monster. I have a Dutch Hill, corn tripod.
Set up some sort of tribrach, and adapter, (Total station works well), center it well, and then get to work down below, modifying the monument, Finally, take a straight edge, and pencil, or a scribe, and a bit of spray paint, and scribe the location in the top of the usually aluminum cap, and lightly punch it. Now, I can set it with close to mm accuracy. At least, that's the goal.
I don't do it very often. But, I want the path to accurate productivity to be smooth, and fast. I I sure don't want Kent MC to complain! 🙂
Nate