Trimble X7 - Best practice in tunnel surveying

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GPTag
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Trimble X7 - Best practice in tunnel surveying

Post by GPTag »

I am looking for the best practice for tunnel surveying with the Trimble X7. The conditions do not allow SX10/12 (too long recording time) or MX90 (not accurate and dense enough point cloud) recordings in the field.

Does anyone have experience with tunnel shots with the Trimble X7? What is the best way to proceed?
The C2C registration worries me a little. Is it possible to calculate a georeferencing per scan station (with the "precise point" mode)?

I am grateful for any input.

Best regards
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Re: Trimble X7 - Best practice in tunnel surveying

Post by kpob46 »

How long is the tunnel that you have to survey? I would not rely on C2C for registration within a tunnel. Certainly use spherical targets, if you can, for registration.
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Re: Trimble X7 - Best practice in tunnel surveying

Post by benoit.lachapelle »

Yes, the C2C in tunnel isn't a good idea. I would go with artifical targets, spheres to connect scan to scans and some checkerboard here and there to georeference it and lock the point cloud to the control network.

In that case, you can use Perspective/Fieldlink just to do a coarse registration with cloud to cloud, but than upload the full project in Trimble Realworks to do a final registration with targets and controls.

cheers,
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Re: Trimble X7 - Best practice in tunnel surveying

Post by GPTag »

kpob46 wrote: Tue Jan 11, 2022 7:26 pm How long is the tunnel that you have to survey? I would not rely on C2C for registration within a tunnel. Certainly use spherical targets, if you can, for registration.
The tunnel is about 500m long.
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Re: Trimble X7 - Best practice in tunnel surveying

Post by landmeterbeuckx »

For tunnel surveying always, i mean always have targets measured in with a total station.
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Re: Trimble X7 - Best practice in tunnel surveying

Post by GPTag »

Thank you for your feedback.
I will work with spheres in the field and Trimble Realswork in the office.
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Re: Trimble X7 - Best practice in tunnel surveying

Post by rollorigby »

One thing to bear in mind, if the tunnel is curved then the wall on the inside of the curve will have a much tighter angle of incidence meaning reduced point density and often very large shadows from very small objects. Being in a tunnel you can't set up further back, so the only solution is reduce scan spacings.
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