CRPIX
CRPIX refers to a set of keywords in the FITS (Flexible Image Transport System) World Coordinate System (WCS) that specify the pixel coordinates of the reference point for each coordinate axis. For each axis i, CRPIXi records the pixel position in the image where the corresponding world coordinate value CRVALi is defined. In a typical 2D image, CRPIX1 and CRPIX2 identify the reference pixel along the x and y axes, respectively.
The reference point serves as the anchor for the WCS transformation from pixel space to world space.
CRPIX values are typically chosen to place the reference pixel within the image frame, commonly near the