What you want is a few lasers of known wavelengths (RGB?) pointing at known angles such that, from the camera's perspective, they appear as lines (ie they aren't perpendicular to the plane of the photo sensor).

A calibration image(s) can be made before each shot. Possibly the resulting image correction can be integrated in to the camera too.

The laser wavelengths are a substitute for the color chart. The laser angle means you get a reading at each distance (ie in the image, each point on the laser "line", corresponds to a distance.)