RGBA conversion to pointcloud2 format fail

[smichaud]

Using the function: "PointMatcher_ros::pointMatcherCloudToRosMsg" with a color descriptor of 4 values (RGBA) does not create the proper RGB8 color for the ROS pointcloud2 data.

A quick fix is to directly set the name to "rgb" (i.e. pointField.name = "rgb";) at this line :
https://github.com/ethz-asl/ethzasl_icp_mapping/blob/master/libpointmatcher_ros/src/point_cloud.cpp#L415