Celestial Coordinate System Routines

The following routines are provided to help calculate the transformation between pixel location in an image and the corresponding celestial coordinates on the sky. These support the following standard map projections: -SIN, -TAN, -ARC, -NCP, -GLS, -MER, and -AIT (these are the legal values for the coordtype parameter). These routines are based on similar functions in Classic AIPS. All the angular quantities are given in units of degrees.

1

Get the values of all the standard FITS celestial coordinate system keywords from the header of a FITS image (i.e., the primary array or an image extension). These values may then be passed to the routines that perform the coordinate transformations.

  int fits_read_img_coord / ffgics
      (fitsfile *fptr, > double *xrefval, double *yrefval,
       double *xrefpix, double *yrefpix, double *xinc, double *yinc,
       double *rot, char *coordtype, int *status)

2

Get the values of all the standard FITS celestial coordinate system keywords from the header of a FITS table where the X and Y (or RA and DEC coordinates are stored in 2 separate columns of the table. These values may then be passed to the routines that perform the coordinate transformations.

  int fits_read_tbl_coord / ffgtcs
      (fitsfile *fptr, int xcol, int ycol, > double *xrefval,
       double *yrefval, double *xrefpix, double *yrefpix, double *xinc,
       double *yinc, double *rot, char *coordtype, int *status)

3

Calculate the celestial coordinate corresponding to the input X and Y pixel location in the image.

  int fits_pix_to_world / ffwldp
      (double xpix, double ypix, double xrefval, double yrefval,
       double xrefpix, double yrefpix, double xinc, double yinc,
       double rot, char *coordtype, > double *xpos, double *ypos,
       int *status)

4

Calculate the X and Y pixel location corresponding to the input celestial coordinate in the image.

  int fits_world_to_pix / ffxypx
      (double xpos, double ypos, double xrefval, double yrefval,
       double xrefpix, double yrefpix, double xinc, double yinc,
       double rot, char *coordtype, double *xpix, double *ypix,
       int *status)