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

This routine provides a faster version of calls to xyzs2c and xyzwrite
for the case that the calling program provides 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)). xyzpixwr takes care of writing the datacube.
Using this routine instead of xyzs2c and xyzwrite reduces the overhead
by more than a factor 10.

    Input:
      tno           image file handle
      pixelnr       pixelnr to be read from virtual cube
      value         pixel value
      mask          FALSE indicates pixel is undefined                        
