The TAN_PIXELS cameraGeom coordinate system (the position on a detector if there is no optical distortion) is presently defined with respect to the center of the detector – i.e. a star at the center of the detector will have the same position in PIXELS and TAN_PIXELS coordinates. That is a mistake. TAN_PIXELS should be defined with respect to the center of the focal plane, since it then reflects the effects of having optical distortion or not.
Fixing this will help meas_astrom match stars. The effects of not fixing it are making the matcher search farther for a fit. As long as we allow sufficient offset in the matcher config the current system will work, but it is not ideal.