Set up total station on the tilt to look vertically down.

Why not set the instrument up correctly and use a 90 degree optical prism so your zenith angle can be exaggerated to 60+ degrees? I used on when aligning a 250' cold box from less than 200' away. Worked great!

Talk to the manufacturer to see if the bearings will handle the stress/torque of operating at that extreme. Also ask if the bearings will handle working upside down.

"It's all ball bearings these days."

good point

> Why not set the instrument up correctly and use a 90 degree optical prism so your zenith angle can be exaggerated to 60+ degrees? I used on when aligning a 250' cold box from less than 200' away. Worked great!

Sounds good, where would I get one and how do I use it? We're not talking about a diagonal eyepiece for sighting upwards are we?

A 90 degree prism attached to the objective might work if it projected out far enough.

> Sounds good, where would I get one and how do I use it? We're not talking about a diagonal eyepiece for sighting upwards are we?
>
> A 90 degree prism attached to the objective might work if it projected out far enough.

Yes, the dealer called it a 90 degree prism, interchangeable with the standard eye piece. Cost is about $600 (2 years ago). You will have to get your equipment dealer to find one for your specific instrument. I believe Topcon and Sokkia instruments have the same eye piece. I know where 2 are that fit the Sokkia Set 3X and most Topcon instruments.

If it works for viewing elevated targets, why wouldn't it work for lower ones as well? Your HI would have to be lower, but your only limitation would be the instrument itself.

I do have a diagonal eyepiece but the telescope can't look straight down through the instrument itself. Upwards no problem, just the handle to avoid.

"It's all ball bearings these days."

That may be true. But, not all ball bearing bearings are created equal. A phone call is a cheap education.

Well stated and well understood.

When I first read your post, I couldn't help but think of 'fletch' and the ball bearing statement.

Now, when I just read your response, I initially thought you were questioning the bearing of the ball bearing (that is to say the basis of the bearings of the bearings), not the weight bearing on the bearings.

It's got to be past quittin' time. Y'all have a good one.

Why would you need to do that.

Sight the optical plumb and you are looking straight down.

B-)

"...Sight the optical plumb and you are looking straight down..."

Straight? Yes.

Down? Yes.

Straight Down? Probably not to the required accuracy.

Here's how they did it at the Anaconda mine in Butte, Montana years ago

I acquired this from the estate of a mining engineer from Montana a few years ago.

Mate of mine used to use a Leica 1200 with minecad as an ad-hoc CMS. The 1200 would be attached to a boom, upside down or right way up, and wheeled out into a void. Shoot 3 targets for control and let it "scan".

Astonishingly that instrument still turned good angles after several years of this sort of use, but then the 1200's were always rather robust.

How do you know your 45° plane is correct?

45º doesn't have to be precise. You're controlling it via the 3 resected stations.

This is pretty common practice. A lot of scanners can't be levelled to the sort of accuracy required for most survey jobs, so they're controlled via multiple targets, established by conventional instruments.

> 45º doesn't have to be precise. You're controlling it via the 3 resected stations.
>
> This is pretty common practice. A lot of scanners can't be levelled to the sort of accuracy required for most survey jobs, so they're controlled via multiple targets, established by conventional instruments.

Yep, turn off the compensator and resection.

huh... who'da thunk it. gonna have to try that sometimes

> > 45º doesn't have to be precise. You're controlling it via the 3 resected stations.
> >
> > This is pretty common practice. A lot of scanners can't be levelled to the sort of accuracy required for most survey jobs, so they're controlled via multiple targets, established by conventional instruments.
>
> Yep, turn off the compensator and resection.

so you're saying the standard resection/free-station would work with the instrument on the tilt?
I would have thought the horizontal and vertical angles would be wrong so throw (big) errors in the free-station.