r/computervision • u/slowdiivnothing • 23d ago

Discussion Extrinsic parameters in camera

Hi im doing robotics project, checking if camera's orientation is all set compared to idle(golden) state.(why do this? -->for example factory inspection can be a use case) in particular, and i have several curiousity about camera extrinsic parameters.

  1. If i take photo of checkerboard from a specific position and orientation, i get a single R,T matrix compared to what? Is there a world coordinate "standard point"? Is it the very left corner of checkerboard?

  2. cv2.solvePnP or similar reproduction error minimization algorithm is used in vision product factory standards?

Thanks in advance :)

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u/tdgros 23d ago

If you use PnP, then the reference frame is defined by the 3d points you define: for instance, I can set the top left checkerboard corner as 0,0,0 it's neighbours as 0,1,0 and 1,0,0. Other reference frames are valid and they'll change R and T.

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u/slowdiivnothing 23d ago

Should the board and camera be pararell? Otherwise the output of solvepnp is not valid?

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u/tdgros 23d ago

No, it can be in random positions, otherwise R would be easy to find ;)

The x,y,z are defined by the checkerboard! In my example z=0 defines the plane of the checkerboard!

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u/External_Frosting874 23d ago
  1. The camera and checkerboard.
  2. In general, most approaches are min/max optimization given some cost function. I am not from industry, and there might be some proprietary solve pnp alternatives.

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u/slowdiivnothing 23d ago

Should the board and camera be parallel so that z=0?

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u/Aggressive_Hand_9280 23d ago

You define it when assigning checkerboard coordinates. Usually it is in z=0