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UPDATE:

After much trial and error, I have given up on trying to get this to work with a chain of nodelets. It is so much easier to do using the C++ examples from http://www.pointclouds.org so I will pursue that approach instead. To extract a sphere, I just modified the cylinder example found at http://www.pointclouds.org/documentation/tutorials/cylinder_segmentation.php#cylinder-segmentation

[Original question now follows.]

Hello,

I am able to successfully extract planes from a Kinect depth image using Diamondback under Ubuntu 10.04 and using the following launch file:

<launch>
  <node pkg="nodelet" type="nodelet" name="pcl_manager" args="manager" output="screen" />

  <!-- Run a Voxel Grid filter -->
  <node pkg="nodelet" type="nodelet" name="voxel_grid" args="load pcl/VoxelGrid pcl_manager" output="screen">
    <remap from="~input" to="/camera/depth/points" />
    <rosparam>
      filter_field_name: z
      filter_limit_min: 0.5
      filter_limit_max: 1.5
      filter_limit_negative: False
      leaf_size: 0.01
    </rosparam>
  </node>

  <!-- Run a Planar Segmentation filter -->
  <node pkg="nodelet" type="nodelet" name="sac_plane" args="load pcl/SACSegmentation pcl_manager" output="screen">
    <remap from="~input" to="/voxel_grid/output" />
    <rosparam>
      model_type: 0
      distance_threshold: 0.01
    </rosparam>
  </node>

  <!-- Then Extract the Inlier Points -->
  <node pkg="nodelet" type="nodelet" name="extract_plane" args="load pcl/ExtractIndices pcl_manager" output="screen">
    <remap from="~input" to="/voxel_grid/output" />
    <remap from="/extract_plane/indices" to="/sac_plane/inliers" />
  </node>
</launch>

And now I would like to extract a sphere (a 6" ball sitting on a table about 1 meter away from the Kinect) using a similar technique. I was hoping it would be as easy as changing the SAC model_type from 0 to 4 but the following launch file generates the error and warning:

[ERROR] [1299428614.657650314]: [pcl::SampleConsensusModelSphere::optimizeModelCoefficients] Not enough inliers found to support a model (0)! Returning the same coefficients.
[ WARN] [1299428614.657849802]: [/sac_sphere::input_indices_callback] No inliers found!

Here is the launch file I tried for extracting a sphere:

<launch>
  <node pkg="nodelet" type="nodelet" name="pcl_manager" args="manager" output="screen" />

  <!-- Run a Voxel Grid filter -->
  <node pkg="nodelet" type="nodelet" name="voxel_grid" args="load pcl/VoxelGrid pcl_manager" output="screen">
    <remap from="~input" to="/camera/depth/points" />
    <rosparam>
      filter_field_name: z
      filter_limit_min: 0.5
      filter_limit_max: 1.5
      filter_limit_negative: False
      leaf_size: 0.01
    </rosparam>
  </node>

  <!-- Run a Sphere Segmentation filter -->
  <node pkg="nodelet" type="nodelet" name="sac_sphere" args="load pcl/SACSegmentation pcl_manager" output="screen">
    <remap from="~input" to="/voxel_grid/output" />
    <rosparam>
      model_type: 4
      distance_threshold: 0.01
    </rosparam>
  </node>

  <!-- Then Extract the Inlier Points -->
  <node pkg="nodelet" type="nodelet" name="extract_sphere" args="load pcl/ExtractIndices pcl_manager" output="screen">
    <remap from="~input" to="/voxel_grid/output" />
    <remap from="/extract_sphere/indices" to="/sac_sphere/inliers" />
  </node>
  
</launch>

I am using VGA/30Hz resolution for both RGB and depth. The sphere is a 6" ball sitting on a table about 1 meter away from the Kinect. I have tried different leaf sizes from 0.01 to 0.0001 meters with the same result. I have also tried different distance_thresholds from 1.0 to 0.0001 with the same result. Both the raw depth image and voxel_grid image look very "sphere-like" in RViz. However the point cloud on the /extract_sphere/output topic is always blank or only has a few points roughly in the location where the ball is. Any pointers would be appreciated!

--patrick

UPDATE:

After much trial and error, I have given up on trying to get this to work with a chain of nodelets. It is so much easier to do using the C++ examples from http://www.pointclouds.org so I will pursue that approach instead. To extract a sphere, I just modified the cylinder example found at http://www.pointclouds.org/documentation/tutorials/cylinder_segmentation.php#cylinder-segmentation

Originally posted by Pi Robot on ROS Answers with karma: 4046 on 2011-03-06

Post score: 1

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Comment by kk on 2013-07-12:
hi can you help me to detect planes ?? im struck ...

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Some of the SAC methods only work when a large percentage of the points are part of the target model. You might want to try using a different method, though I don't know enough to suggest a specific method. Examples are RANSAC, RRANSAC, MLESAC, MSAC, etc.

Also, the number of iterations might be important. I'm unaware of what the default number is, but if it's low, pumping it up might help (but will slow things down).

Originally posted by Asomerville with karma: 2743 on 2011-05-24

This answer was ACCEPTED on the original site

Post score: 0

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Comment by Vincent Rabaud on 2011-06-17:
Please edit the original question and post an update with your answer, or please add an answer and accept it.

Comment by Pi Robot on 2011-05-29:
After much trial and error, I have given up on trying to get this to work with a chain of nodelets. It is so much easier to do using the C++ examples from http://www.pointclouds.org so I will pursue that approach instead. To extract a sphere, I just modified the cylinder example found at http://www.pointclouds.org/documentation/tutorials/cylinder_segmentation.php#cylinder-segmentation.

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