Wrong Lidar Point Height when Tilt Angle is Non-Zero.

[DavidMansolino]

Describe the Bug
When the tilt angle of a lidar is not 0, it may happen that the lidar points are 'too high'.

Steps to Reproduce

1. Can easily be reproduce with the Velodyne HLD64 and a flat ground.
2. Or with this world: test0.zip

Expected behavior
The lidar point should all be at the same height than the floor.

Screenshots

System
System: Windows 10 64-bit
Processor: Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz
Number of cores: 4
OpenGL vendor: NVIDIA Corporation (0x10de)
OpenGL renderer: GeForce GTX 970/PCIe/SSE2 (0x13c2)
OpenGL version: 4.6.0 NVIDIA 416.94

[DavidMansolino]

Without tilt angle:

With a title angle of -0.2:

[DavidMansolino]

The bug is present only for spherical cameras.

[DavidMansolino]

I found the exact reason, the problem is at the merge_spherical shader level.
Indeed because of the spherical deformation, the wrong vertical pixel is selected, in case of lidars we should perform the deformation only horizontally but not vertically.

[DavidMansolino]

Tilting the camera doesn't seem to be a good idea, in case of spherical camera, it is really a mess if the cameras are tilted (sub-cameras border don't coincide anymore).
Instead of tilting the sub-cameras, it seems safer to create a bigger field of view and use only the interesting part (so that the orientation of all the sub-cameras is conserved), but this will require some re-factorization.