What prism do you use to measure distances over 1000 feet?

[sako]

I use my MT1000 prism to measure distance up to 800 feet with my Trimble S7. Anything beyond that, I try my Trimble SLR prism. What prism do you use for long range?

[Jim Frame]

I run a GeoMax robot, and I use a Leica GMP101 tilting mini prism pretty much all the time. I think I've gotten about 1600 feet with it. In the last 10 years I've had to take half-mile shots on a handful of occasions, in which cases I used a Leica GPR121 standard-size prism.

[sako]

I run a GeoMax robot, and I use a Leica GMP101 tilting mini prism pretty much all the time. I think I've gotten about 1600 feet with it. In the last 10 years I've had to take half-mile shots on a handful of occasions, in which cases I used a Leica GPR121 standard-size prism.

Jim, How does the radio of Geomax work in that distance? My Trimble radio keep disconnecting after 800 feet.

[Jim Frame]

Jim, How does the radio of Geomax work in that distance?

It works pretty well as long as I have good line of sight. I have a 5" (9dBi?) antenna on my data collector, which undoubtedly plays a role in effective distance.

[sako]

Jim, How does the radio of Geomax work in that distance?

It works pretty well as long as I have good line of sight. I have a 5" (9dBi?) antenna on my data collector, which undoubtedly plays a role in effective distance.

I couldn't find the diameter of the prism you mentioned, but I assume it's 20 MM, isn't is too small for distance of over 1000 feet? How does the instrument track and find it? The line of sight you mentioned shouldn't matter in case of radio connection. The antenna of Trimble is 4" long, same as the antenna for TSC3.

[Jim Frame]

20 mm sounds about right, I don't have one in front of me right now. 1600' is at the outer limit of the GeoMax lock range to a mini, but it does work. The published autolock range to a standard circular prism is 3300', but I've never tested it beyond half a mile.

Tracking at 1600' not so much, it loses lock easily at that distance, but with a stationary mini prism it will find and lock once you rough-aim the instrument via joystick and execute the standard search routine.

[sako]

Jim,
The beauty of robotic surveying is that you are always there where it's being surveyed, but with the radio signal keep loosing and the instrument trying to reconnect, it's NOT fun. I'm surprised that the Geomax radio is still connected at 1000 fret.

[DWoolley]

I am not sure I have a good visual in my mind.

Why not set up a tripod and glass at 1,000 feet and measure it from behind the instrument? A single prism should be good for 2,000 feet plus.

[Lord, please don't let the answer involve a survey crew with only one tripod in the truck (or '77 Datsun B210). Hear my prayer].

DWoolley

[sako]

Mr. Woolley,
I have used the same process as you mentioned. I just wanted to know what other robotic instrument users are experiencing in my situation.

[Jim Frame]

Why not set up a tripod and glass at 1,000 feet and measure it from behind the instrument?

I rarely look through the gun anymore. About the only time I do is for reflectorless shots, and I don't take many of those. And I rarely set up a fixed backsight anymore, either.

I still carry 4.5 tripods in the truck, though: 2 each Leica GST20, 2 each Seco 5115 fixed-height, and a Seco prism pole tripod (that's the 1/2).

[RAM]

tried and true, wild 3 bucket on a tripod. O offset. works to 8-10k'

[T. S. Higgins]

We use Leica GPH1Ps for deformation monitoring, with observations up to 2500'. Haven't encountered any issues with those prisms, whereas some of the cheaper options did not produce as consistent results.

We do not use robotic methods over that kind of distance, since the centering errors that you'll get with the autolock become more significant at that range, at least for our application.

[David Kendall]

We use Leica GPH1P for deformation monitoring, with observations up to 2500'

Do they make a target plate for that setup? Seems like it might be hard to see it at long distances

[Jim Frame]

We use Leica GPH1Ps for deformation monitoring, with observations up to 2500'.

Nice glass, but pricey ($1400-ish). I'm surprised you found any consistency advantage over a standard Leica prism (e.g. GPR1), especially at 2500'.

[T. S. Higgins]

We use Leica GPH1P for deformation monitoring, with observations up to 2500'

Do they make a target plate for that setup? Seems like it might be hard to see it at long distances

No target plate unfortunately. At the ranges we're using it we haven't had any issues with visibility, you can clearly make out the individual prism faces and find center without much trouble. I was hoping to have target plates but when I requested them, they didn't have anything available.

We use Leica GPH1Ps for deformation monitoring, with observations up to 2500'.

Nice glass, but pricey ($1400-ish). I'm surprised you found any consistency advantage over a standard Leica prism (e.g. GPR1), especially at 2500'.

It isn't a huge difference to be honest, but enough to be noticed in the reports. The main driving force behind using it over the GPR1 is to meet an overall error budget for the monitoring that we perform. We didn't pay anywhere near the $1400 because we were buying in bulk, but they're definitely expensive. Outside of fringe cases like performing deformation monitoring of a federally regulated dam like us, I think anybody would be fine with the GPR1.