How to convert Point Cloud Data from AstraS Depth image?

Technical Support & Q&A
1

Hi. everyone.

Now I trying to convert point cloud data from ASTRA depth image.
But I don’t know IR sensor focal length.

I actually measured the depth image.
Calculation result became the next focal length .
fx = 625.0
fy = 595.0
But I do not know whether or not the correct answer .

Would you tell me the focal length of IR sensor?

fx = 625.0;
fy = 595.0;
w = 640;
h = 480;

for j=1:h
for i =1:w
world_z = Depth(j,i);
world_x = ((i-240)./fx)*world_z;
world_y = ((j-320)./fy)*world_z;
end
end

1 Like
2

Are you using OpenNI or Astra SDK? Both provide built-in ways to convert depth-to-world points.

3

Hi Josh. Thank you for reply.

I am using OpenNI now.

Both provide built-in ways to convert depth-to-world points.

Wow. I didn’t know, I can use convert depth-to-world points by Astra SDK.

Is this function ? → “astra_convert_depth_to_world”
I want to use this function!
I’m looking for a document of how to use this function .
But not find .

Would you teach me, how to use function!

4

In Astra SDK, if you start the PointStream, it will deliver you depth frames where each pixel has already been converted to a Vector3f which is x, y, z in real world millimeters.

In OpenNI2, there is a CoordinateConverter class where you can convert depth to world or vice versa.

5

@josh

I’ll try it.
Thank you very much!!!

6

Hello, I know it’s been a while but I’m trying to get this data exactly but my problem is that the information i get is exactly identical in x,y,z… the data is like this(Getting the PointMap):

11 11 11 255
100 100 100 255
…

For every point, Idk how to convert this into the actual coordinates. My first intuition told me that it was the depth in mm repeated in x,y,z. But I understood from the explanation given here that you actually get the 3D coords. Not again the depth info.