Fix GetDistance() issue for SoftwareDevice in C#

[hsuys]

Fix GetDistance() issue for SoftwareDevice in C#

changes:
add depth_units field to type SoftwareVideoFrame and class AddVideoFrame

Tracked on: [DSO-19246]
Original issue: #12170

[Nir-Az]

Thanks @hsuys .
@maloel can you help with reviewing this?

I don't know this deeply but the SW device can handle DEPTH_UNIT option no?

Do we really want to set it on each frame?

[maloel]

Do we really want to set it on each frame?

My first question when seeing the user's problem was the same:

• Why not just set the DEPTH_UNITS in their software-sensor??

But:

• even in Python, our software_video_frame object has no field for depth_units
• the C++ code assigns the frame's depth-units (which, with a regular camera, comes from metadata) from this field in the structure, per frame
• the C++ structure for software_video_frame has no initialization for this field; I assume it's initialized to 0
• the code for get_distance() just uses this data in the frame (get_units()), without checking if it's zero

So, IMO, the fix from @hsuys is technically correct: the user should be able to specify the depth-units per frame, as we allow in C++. However, this should be done in Python, too, and the rest of the wrappers.

Furthermore, I believe the broader issue is: what happens if, like up until now, the user couldn't or didn't set this field? I think the proper thing to do is get the sensor from the frame and query it for DEPTH_UNITS (query_units() is already written but not made use of...) if the frame-specific units are 0.

The latter would also take care of the user's problem, without specific fixes in C# and Python (or other wrappers) -- assuming the user does not need to set the depth-units per frame.

[maloel]

• the C++ structure for software_video_frame has no initialization for this field; I assume it's initialized to 0

I wrote a small unit-test and checked:
The field is uninitialized. I get garbage, not 0. That would also explain the user's "bogus number".

[maloel]

I think the default should be 0, not 0.001.
That way, it will check DEPTH_UNITS after I do my own PR.
We cannot assume to know what units the user uses.

[hsuys]

Done. Default to 0.
Also added and initialized the depth unit when constructing sw depth frame in the software-device tutorial.