%N xyzpixrd %F $MIR/src/subs/xyzio.c
%D Get a pixel from a dataset
%P bpw
%: image-i/o
%B
      subroutine xyzpixrd( tno, pixelnr, value, mask )
      integer    tno
      integer    pixelnr
      logical    mask
      real       value

This routine provides a faster version of calls to xyzs2c and xyzread
for the case that the calling program needs single pixels. It should
be used after a call to xyzsetup was used to set up zero-dimensional
subcubes. The calling program can then loop over all pixels (from 1 to
vircubesize(naxis)). xyzpixrd takes care of reading the datacube.
Using this routine instead of xyzs2c and xyzread reduces the overhead
by more than a factor 10.

    Input:
      tno           image file handle
      pixelnr       pixelnr to be read from virtual cube

    Output:
      value         pixel value
      mask          FALSE if pixel was undefined                              
