Relative Depth to Absolute through Interpolation

[panagiotamoraiti]

Hello,

I am trying to estimate the true depth in cm from the relative depth and i found out i need to do some kind of calibration based on known depths.

I use the following code:

  # Use depth anything model to generate depth map
  depth = model.infer_image(img) # HxW raw depth map in numpy

  # Relative depth normalized
  depth = (depth - depth.min()) / (depth.max() - depth.min())
  depth = 1 - depth

  # Get relative depth
  relative_depth = depth[center_y, center_x]

  # Convert relative to absolute depth
  rel_depths = np.array([0.04, 0.202, 0.205, 0.92])
  abs_depths = np.array([85, 110, 117, 180])

  
  # Estimate calibration function
  calibration_fn = interp1d(rel_depths, abs_depths, kind='linear', fill_value="extrapolate") 

  # Absolute depth calculation
  absolute_depth = calibration_fn(relative_depth)

I use interp1d method to find out the depth and my code works very well.
I want to ask what is the difference between the lstsq method mentioned on issue #157.

Is my approach correct??? I tried lstsq method but didn't get good results and i don't know why.
If someone can give some intuition it will be greatly appreciated!