Cool!
Dave
This from Surveying Prisms Basics:
"Every surveying prism has a nodal offset. Surveying Prisms and holders that are not in the nodal position however, can cause angular errors when using the prism apex as a target if it is not perfectly pointed toward the measuring instrument."
A prism is not "Nodal" unless its nodal offset coincides with the pivot point.
Dave
I second this. The tracking setting you use (passive vs. active) will make a small difference, but I have not noticed accuracy suffering other than for shots very close to the instrument. We have used our S6's w/ MT1000's for all kinds of layout and have not noticed any issues, but we still try to make an effort to keep one prism pointed to the gun.
David - take a second look at the manual regarding the vertical angle tolerances for the MT1000. I believe it says 15° for active mode and 30° for passive mode.
Alan,
Here's from the Trimble S6 manual in the section on using the MT1000:
Dave
My point was just that if you are in between 15° and 30° the MultiTrack is still an acceptable target as long as it is used in passive mode. In my experience I have found that to be true. I guess I read your post above as saying that beyond 15° from horizontal the MultiTrack was unusable. Sorry for the confusion.
Alan,
So you're getting good results between 15 and 30 degrees of horizontal, as long as you use Passive Mode? I hadn't thought of using the MT1000 in Passive Mode. Looks like some testing is in order. Thank you.
Dave
We have the smaller prism, except painted yellow with 0 or -30 offset and with a Trimble sticker (and pricetag)
It is the best thing we have for doing setout - much easier than the 360 active
I like the fact that the spike is sharp and strong enough that, if necessary, I can stick it into a peg and have it stay there while I run back to the instrument.
The only real disadvantage is that when we use it we have to turn our safety vests inside out so the passive tracking does not try to track the reflective strips on them
Looks like we are getting somewhere Dave! I still want to clarify a few things...
I can understand why you were asking how do you know if a prism is nodal...seco makes mini prisms that look exactly like the one you pictured that are not nodal. http://www.engineersupply.com/seco-mini-stakeout-prism-with-site-cones-6405-10.aspx
So I guess if you want the -30 mm offset you go with the one in the link above, understanding its not nodal.
Why did no one suggest using the larger 62 mm pole? If the point errors are reduced because it is nodal, is there still an issue? Is it just a matter of the weight? It seems like the 62m would be good for a backsights correct?
What are peoples setups like? Working for a construction company and having to climb forms, layout on top of walls, walk on rebar....I use a 30" rod that expands to 5' with a mini bipod. The seco mini prism pictured above would be great because I could put it on the bottom of the pole. Do you use a rod when you layout anchor bolts??
Doka1,
"...having to climb forms, layout on top of walls, walk on rebar...."
Yep. I like the idea of the 30" rod. That would make it easier to lay out anchor bolts on a mat footing. Before, I've always used a mini, but with an I-man at the gun. Now I'll have to adapt to this brave new robotic world. I never thought about having the active-track prism on top and the Nodal mini on the bottom. Genius! Best of both worlds, and you can keep the data collector in its cradle on the pole. The only problem would be putting a blindfold on the prism not being used, to switch between the MT1000 and the mini. Oh, and are there 5/8-11 threads on top of that Nodal mini?
Dave
Jim,
"...we have to turn our safety vests inside out..."
For high-precision setout, I think a two-man crew with an old-fashioned non-robotic gun is easier, but companies don't want to pay an I-man to "stand around at the gun all day". Sigh.
Dave
lol, I wasn't thinking of two prisms, but it could work I guess. I am just saying that carrying the mini in your pouch kind of sucks because its too hard to read the screen and hold the mini. Btw, we have 3 robots in our company and the consensus among the three of us is that we don't want carrying around 4-5k around the jobsite (multitrack prism, radio for ts, computer for ts, pole...)
what about the 62mm prism dave???? what are your thoughts?
I feel comfortable with the 30" height and the bipod. When I check my rod in the office, I set up the 30" pole with the bipod and spin it, the bubble is very sensitive. I know this may sound trivial to some people but the 30" pole height seemed too high for me before. But then I think about how much we used to use a plumb bob with the prism on the line and feel a lot better with the 30" steady rod than the instrument man plumbing down 30". Using a plumb bob with a prism mount is truly an art....
Doka,
"Using a plumb bob with a prism mount is truly an art...."
Agreed.
"...carrying the mini in your pouch kind of sucks because its too hard to read the screen and hold the mini."
Yep.
"What about the 62mm prism?"
Makes a nice backsight, and it's cheaper than the mini. But for use with a robot, I don't know that the extra diameter adds any benefit. If using the 62mm made the robot less likely to chase vests, then it would be a hands-down choice. Does it?
"...the consensus among the three of us is that we don't want carrying around 4-5k around the jobsite (multitrack prism, radio for ts, computer for ts, pole...)"
And I also think leaving a $25K+ gun unguarded at a busy construction site is insanity and needlessly risky.
Doka, what part of the country are you in?
Dave
You are right about the gun, but honestly using the robot and be able to setup a distance from all of the action makes things a lot easier. Tts not that I am setting up miles away with the robot, but I can be more strategic about the placement, and perform resections quickly now with the software.
I work in New Jersey, on commercial foundation projects. What about you?
Doka,
I'm a union carpenter. I used to work in Las Vegas on casino projects, back when they used to build things. I haven't worked in 2-1/2 years now, so I'm thinking about travelling. I've got a possible job in Sacramento starting in the next month.
Next to the SacTown project site is a parking garage, which would be a really nice, protected spot to set up the robot and overlook the jobsite. But I worry about the garage moving. (Sun, cars, etc...)
I haven't had a lot of luck with getting really tight resections. I suppose the robot could wrap angles pretty quick to get things tighter, but I generally have only one backsight, so I'd have to walk fast with the prism rod from control to control. I thought about using some tightly measured sticky targets on buildings around the project to get a more accurate resect.
Dave
anyone seen or used the new AT360 target yet?
I am curious if it will be any more accurate than the MT1000 and if so, how?
I only find that the MT1000 vertical can be out by up to 5mm in active mode compared to passive mode. Would be nice to have something more lightweight though.
25mm SECO -17.5mm (Nodal) with a 20' vial. Extremely precise setup, within .001'/.3mm of the best adjusted traverse kit time & time again. Use this setup with a Sokkia DX-201AC & AP series Sokkia 62mm/-40mm Nodal on AP41adapters. Haven't pulled out the plumb Bob for anything but crossing bolts since getting it.