NAME:
  posarr
 PURPOSE:   (one line only)
  Generate array of positions that match an image
 DESCRIPTION:
 CATEGORY:
  Miscellaneous
 CALLING SEQUENCE:
  posarr,nx,ny,xarr,yarr
 INPUTS:
  nx - width of array
  ny - height of array
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  X0 - location of the X origin in the image, default=0
  Y0 - location of the Y origin in th eimage, default=0
  SCALE - scale factor of image pixel to your desired x,y scale,
             default=1.0
 OUTPUTS:
  xarr - Array with the x position of each pixel in the array value
  yarr - Array with the y position
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  2016/09/23, Written by Marc W. Buie, Southwest Research Institute