Beam spacing methods doesn't match with oculus

[woensug-choi]

Sonar specification sheet has parameters to define beam angles,

• Number of beams

• Horizontal Aperture (FOV)

• Beam Separation
  It seems that the azimuth angles (beam angles) in the sonar image should be uniformly spaced with the given beam separation. But it was not true for both simulation and the experiment data.

• Simulation beam angle spacings

  • As long as the plugin is based on the depth_camera, it would be difficult to modify it to evenly spaced or other spacing designs. The depth camera is obtaining data mapped on a z-buffer (evenly spaced) and looking at the image from a point make the spacings as shown below.
  • Maybe replacing the depth_camera part with a ray-based point cloud generating plugin can solve this problem.
    

• Experiments (oculus) beam angle spacings

  • I suspect that this beam spacing design is related to hardware design. The way the transducers are aligned.
    

It's more strange that the beam spacings of oculus are not increasing linearly.

[woensug-choi]

With, #19 it will be equally spaced.
To make the beam angle spacing user-definable, importing and modifying https://github.com/lmark1/velodyne_simulator will do.