This directory contains code that read and calculates the Nh value
 using an Nh map construct by Dickey and Lockman.

 hnh.c             FTOOL C wrapper
 nh.f              program
 nhinit.f          get the parameters 
 nhmake.f          read and interpolate the nh value
 nh.par            parameter file  

 nh.hlp            help file 
 Makefile          makefile

 It requires to build the following library : fitsio, xanlib (sla), xpi
 It requires to read the Nh map. 
 Two maps are available:
 1- map 360 X 180 delivery from Bregman. The projection is GLS
    with the usage of the fits convention off by one pixel.
    The pixel size is 1 degree X 1 degree and contains the average value 
    as obtained by Dickey and Lockman.
 2- map 480 X 240 delivery by S. Snowden. The projection is Aitoff
    with apparently the correct fits convention is use. The pixel size is 
    0.675 degrees X 0.675 degrees. The map therefore is resampled from 
    the original average by Dickey and Lockman.
    
 Currently the code uses the second version but it would be better 
 try to get the first map fixed. 
 map file  h1_nh.fits


 May 2000 fixes
 - Change the calling sequence of nhmake.f to return the average 
 and weighted values. This makes easier to include the routine
 in code that build databases.
 - Add an example in the help file
 - At the lower boundery now always check for positive pixel number 
   and start from 1 is negative or 0. This is to avoid changing 
   the search box size, which produces the same result.

 Feb 2001 fixes
  - the position reported by Ed 
       Equinox 2000 RA=21.66183268 DEC=-22.011388 
    is at the boundery of the map. On linux and solaris this
    print a null result on osf this causes a floating and the W3nh
    do not report any message. I have added a message that tell 
    to use a larger distance and this fixes the floating on osf. 

 Apr 2007 fixes
  - Added support for an alternate map by way of the altmap parameter and 
    the usemap parameter, which lets the user choose either the default
    map, the alternate map, or both.
  - Changed the default map to that provided by K. Kuntz, derived from the
    LAB survey HI map.
  - Added output parameters:
                       avnh    - average nH (default map)
                       avwnh   - weighted average nH (default map)
                       alnh    - average nH (alternate map)
                       alwnh   - weighted average nH (alternate map)

  - Fixed fairly serious bug causing nh to skip the first pixel found,
    even if it should be included in the average. This was due to an
    uninitialized variable which was not a problem on OSF, Solaris, or
    older versions of GNU compilers.