3dcircle_segmentation.rst

3D Circle model segmentation

This tutorial exemplifies how to run a Sample Consensus segmentation for circular models. The code attached shows how to find a circle in your point cloud data. The main difference between a 3d circle model and a 2d circle model is the number of output parameters. 3d circle not only outputs the parameters of a circle but its 3d orientation as well.

The code

First, download the dataset circle_input.pcd and save it somewhere to disk.

Then, create a file, let's say, 3dcircle_segmentation.cpp in your favorite editor, and place the following inside it:

.. literalinclude:: sources/3dcircle_segmentation/3dcircle_segmentation.cpp
   :language: cpp
   :linenos:

The explanation

The only relevant lines are the lines below, as the other operations are already described in the other tutorials.

.. literalinclude:: sources/3dcircle_segmentation/3dcircle_segmentation.cpp
   :language: cpp
   :lines: 39-51

As seen, we're using a RANSAC robust estimator to obtain the 3d circle coefficients, and we're imposing a distance threshold from each inlier point to the model no greater than 2cm. We also limit the radius of the 3d circle to 5-15cm..

Compiling and running the program

Add the following lines to your CMakeLists.txt file:

.. literalinclude:: sources/3dcircle_segmentation/CMakeLists.txt
   :language: cmake
   :linenos:

After you have made the executable, you can run it. Simply do:

$ ./3dcircle_segmentation

You will see something similar to:

coeff circle: 1.000000 5.000000 -3.000000 0.100000 -0.000000 -1.000000 0.000000
inliers number:18

You can also look at your point clouds circle_input.pcd, circle_result.pcd:

$ ./pcd_viewer circle_input.pcd circle_result.pcd

You are now able to see the the found circle together with the input data in one viewer. You should see something similar to this: