Aligning scan to Cad

Please post any tips or advice you have in general relating to laser scanning either whilst onsite or office based.
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Aligning scan to Cad

Post by perry » Wed Apr 22, 2015 7:09 pm

Hi all,

If the xyz planes of a scan is in a different orientation to the xyz of a cad system do you rotate the scan or do you model in cad using the scans xyz planes. If you do rotate the scan what advice do you have to ensure the rotation is correct and also at what point should this be done.


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Re: Aligning scan to Cad

Post by Bill-Wallace » Wed Apr 22, 2015 7:54 pm

About 100 different ways to get this done depending on what data you have (known coordinates, etc.) and what systems you are working with.

You either need to learn about registering the point cloud to control or about establishing a user coordinate system or you can use the crude method and move the model to match the cloud. You will find that "Most" CAD systems won't want to move the cloud per-se although some will let you reference user (alternate) coordinate systems. So if you don't care about the actual location of things in space, you could simply move the model to the cloud.

To move the model, you need to establish some common entities in the model and cloud. If the model items are all new stuff (not represented in the cloud), then model in some of things captured by the cloud in a proper position to the new model stuff. I assume you somehow know where this new stuff should be in relation to some existing stuff. Then pick known points on the model, like the corner of a column base plate and move it to the same point in the cloud by picking on the cloud as the "move-to" point. Then using that same point, rotate around the Z (assuming everything is already properly Z up) as needed. If you are a good CAD guy you will know how to do an accurate rotate by reference.

Usually people register (align) the cloud to a known (and shared) coordinate system before bringing to CAD.

Sorry to be vague but just trying to give you some ideas.

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