RANSAC Shape Detection (plugin)

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Introduction

qRansacSD stands for "RANSAC Shape Detection" and is a simple interface to the automatic shape detection algorithm proposed by Ruwen Schnabel et al. of Bonn university.

This is exactly the same implementation as the library shared by the authors on their website (version 1.1).

Therefore, if you use this tool for a scientific publication, please cite the author before citing CloudCompare (which is also very good but less important in this particular case ;).

CloudCompare simply adds a dialog to set some parameters (see below) and a seamless integration in its own workflow.

Usage

Notes:

  • to use this plugin, the user must select a point cloud
  • to obtain better results, you can provide a point cloud with clean normals (otherwise the plugin will compute them itself)

The plugin dialog looks like this:

Cc qRansacSD dialog.jpg

The description of each parameter should appear as a tooltip (appears when leaving the mouse over the corresponding spinbox for a while). The most important one is the number of samples (support points) per primitive. It all depends on your cloud density and the size of the shapes you are trying to detect. For the other parameters, it may be necessary to read the original article.

You also have to select only the kind of primitives you actually wish to detect (see the checkboxes on the left) so as to easily avoid false/unnecessary detections.

On completion, the plugin will create a set of new entities. For each detected shape you get:

  • a point cloud corresponding to the subset of points that supports the detected primitive. The name of the cloud incorporates the estimated primitives parameters
  • the corresponding entity as child of this cloud. Warning: apart for planes, the other primitives are not displayed by default (as they can be much bigger than the actual cloud, especially for spherical or cylindrical portions that may only fit on a very small portion of the complete primitive).
  • each couple (cloud/primitive) is randomly colored
Cc qRansacSD result.jpg