Large Georeferenced pointclouds

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Bexy1977
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Large Georeferenced pointclouds

Post by Bexy1977 »

HI all.

New to posting, but been reading on the forum for a couple of years and it has given me some great insights!

We work in the water industry so we often have quite complex and large pointclouds with complex pipework and valving sets, large areas of open water (without return), complex civil structures and wide open spaces all within the 1 survey.

We currently have, what for us is a large scheme across a whole site of almost 800 scans. We only do a 'simple' geo referencing requirement, using spheres on GPS'd station points to create references.

We use Faro scanners, combination of X330, S150 and S70's and we use Scene for processing to provide ReCap outputs and .pod outputs, depending on our clients.

Usually we create a cluster or a workspace which is our referenced workspace and then add to it, however on this job we are having trouble adding 2 workspaces together. In Scene we can register the 2 workspaces together to a good level, but they wont recognise the geolocation references. If we force these correspondances, then it throws the 2 workspaces out by 150mm.

We don't think that there is anything wrong with the either workspace, and indeed we have already successfully added a different workspace area to the referenced workspace without this issue.

We are a bit stumped as to why this is happening so any ideas or help would be helpful. We don't have access to any other processing software's, or indeed experience in using them.

Thanks in advance.
jamesworrell
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Re: Large Georeferenced pointclouds

Post by jamesworrell »

I'll open with the obvious .. you mention GPS .. is it simply scale factor? 800 scans .. say 400m across the site or between GPS stations/clusters .. 400m x 0.0004 = 160mm.
RJGEOMATICS
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Re: Large Georeferenced pointclouds

Post by RJGEOMATICS »

jamesworrell wrote: Wed Sep 15, 2021 9:48 pm I'll open with the obvious .. you mention GPS .. is it simply scale factor? 800 scans .. say 400m across the site or between GPS stations/clusters .. 400m x 0.0004 = 160mm.
Oh, those evil Grid to Ground scale factors.... Was so much easier back in the MC5 data collector days. Every job started at 5000,5000,100... And that local reference was top of a hydrant, or some bolt on a light standard...

Everything worked, and then some rocket scientist thought it would be intelligent to try and force construction and buildings to use UTM coordinates and scale factors.
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Re: Large Georeferenced pointclouds

Post by smacl »

jamesworrell wrote: Wed Sep 15, 2021 9:48 pm I'll open with the obvious .. you mention GPS .. is it simply scale factor? 800 scans .. say 400m across the site or between GPS stations/clusters .. 400m x 0.0004 = 160mm.
Yep, my thoughts also. To stay georeferenced you'd need to transform the point cloud data into the GPS grid. I'd be going for a 2D conformal transformation here, with a possible uniform level shift, trying to get as many control points as possible into each scan job being transformed. Minimum of 3 would give enough redundancy to get residuals for basic QA. Note that I'd avoid using a 7 parameter or Helmert transformation as you don't want to scale heights in this case and nor do you want any non-plan rotations.
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Re: Large Georeferenced pointclouds

Post by smacl »

RJGEOMATICS wrote: Thu Sep 16, 2021 12:16 amOh, those evil Grid to Ground scale factors.... Was so much easier back in the MC5 data collector days. Every job started at 5000,5000,100... And that local reference was top of a hydrant, or some bolt on a light standard...

Everything worked, and then some rocket scientist thought it would be intelligent to try and force construction and buildings to use UTM coordinates and scale factors.
If only the earth was flat.... :D
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