Implement an Optical Flow Camera

[sshashank124]

Description

Adds a new Optical Flow Camera sensor. Transmits data as an image with uint16 channels where the first channel represents the x-component of the optical flow and the second channel represents the y-component. The value of each channel maps to a float range of [-2, 2] which means that the maximum optical flow that can be represented between two consecutive frames is twice the dimensions of the viewport (image width x height).

Also includes a fix for correctly transmitting 16-bit buffers with the Vulkan backend. This fix was implemented by @Axel1092

Where has this been tested?

• Platform(s): Linux
• Python version(s): 3.6
• Unreal Engine version(s): 4.26

Possible Drawbacks

PythonAPI/examples/manual_control.py code for displaying output of Optical Flow sensor runs a bit slower than real-time.

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This change is 

[Axel1092]

Reviewed 17 of 17 files at r1.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @sshashank124)

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LibCarla/source/carla/sensor/data/Color.h, line 68 at r1 (raw file):

    }

//    operator rpc::Color16bit() const {

If this part does not work better to remove it, not left it commented

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PythonAPI/examples/manual_control.py, line 1117 at r1 (raw file):

            if OPENCV_INSTALLED:
                data_array = np.array(array[:, :, 0:2], dtype=np.float32)
                data_array[:, :, 0] = (data_array[:, :, 0] - 32767) * (2 * image.width / 65535)

I think this transformations are important to understand. Could you please describe in some comments what this operation does?

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Unreal/CarlaUE4/Plugins/Carla/Source/Carla/Sensor/OpticalFlowCamera.cpp, line 17 at r1 (raw file):

  AddPostProcessingMaterial(
      TEXT("Material'/Carla/PostProcessingMaterials/PhysicLensDistortion.PhysicLensDistortion'"));
//  AddPostProcessingMaterial(

These materials as they are not used we could just remove the comented lines.

[Axel1092]

Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @sshashank124)

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PythonAPI/examples/manual_control.py, line 1012 at r1 (raw file):

        self.sensors = [
            ['sensor.camera.rgb', cc.Raw, 'Camera RGB', {}],
            ['sensor.camera.optical_flow', cc.Raw, 'Optical Flow', {}],

Maybe it is better to move this to the end of the list to not change the order of the old sensors

[Axel1092]

Reviewed 3 of 8 files at r2, 12 of 13 files at r3, 3 of 3 files at r4.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @sshashank124)

[Axel1092]

Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @sshashank124)

[Axel1092]

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @sshashank124)

[Axel1092]

Reviewed 2 of 2 files at r5.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @sshashank124)

[Axel1092]

Reviewed 1 of 1 files at r6.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @sshashank124)