Extract Geometry from Clouds

SA can be used to extract features from a point cloud without CAD or any nominal references of any kind. This is done by detecting geometry within proximity to a seed point (or click-point). Press the Geometry button in the Extract Geometry section of the Features tab to bring up the following control.

 

Feature Selection and Cloud interaction

To use this extraction dialog, simply open the dialog so that it is visible, select the geometry button of interest, and then click on a cloud point to define the start of the search region.

 

Normal Direction and Reference

Without a nominal reference, geometry has no directional reference. Predefining a reference object allows all the resulting objects to be correctly oriented. This is important if additional point measurements are going to be taken and the correct offsets need to be accounted for. Object direction can also be reversed individually by selecting the newly built object in the Extract Geometry from Cloud dialog, or in the fit settings of the resulting geometry relationship.

 

Selected Points Only (check box)

When enabled, this option will prompt the user to select the subset of the cloud to consider after selecting the starting point. This can be very helpful for detecting individual features and accelerating the search process by reducing the amount of data to consider.

 

Extraction Tolerance

A single tolerance parameter is presented.

Relative to the seed point, the “ExtractPlane” function tries to grow a plane (or other geometry) and as it grows, it filters out points that are not within this plane tolerance. If data is fairly planar then there is a good chance that the correct set of planar cloud points will be harvested with a tight tolerance. However, if you pick a seed point in a region with adjacent points that are not clearly planar then the plane may start off in a bad orientation. Larger tolerances will increase the likelihood of getting the correct orientation but include more outlier points in the fit. Therefore an optimal balance must be found.

Acceptance criteria for a “good” circle (currently hard coded values included here only as a reference) :