NAME:
  projerr
 PURPOSE:   (one line only)
  Re-project an error ellipse onto a new coordinate system
 DESCRIPTION:
  The new coordinate system is rotated with respect to the one natural
     to the error ellipse.
 CATEGORY:
  Astrometry
 CALLING SEQUENCE:
  projerr,smajor,sminor,pang,rotang,rsmajor,rsminor
 INPUTS:
  smajor - Length of the semi-major axis of the error ellipse (1 sigma)
  sminor - Length of the semi-minor axis of the error ellipse (1 sigma)
  pang  - Position angle of the major axis, measured eastward from
            north [radians].
  rotang - Position angle of the axis to decompose the error along.
              measured eastward from north [radians].
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  intrack - 1-sigma in-track error component
  xtrack  - 1-sigma cross-track error component
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  2019/07/12, Written by Marc W. Buie, Southwest Research Institute