This directory contains an number of utilites to Access TOVS Polar Pathfinder
data. The data come in HDF (version 3.3) format. In order to use the data
the user can has several options:

1) Use commercially or public domain tools to process data.

2) Convert data to non-hdf format given the provided unpacking program.

3) Use the provided access programs in Fortran, C or IDL (Interactive
   Data Language) to interface with their processing routines.


The following utilities are provided:

  unpack : Converts HDF formatted files into flat binary files.
 
  sample_readpathP_c.c : A sample program written in C that shows
			 how to access the data using a C program.
	                 This program is meant as an illustration
	                 of how to use the functions {c,f}readpathP.{c,f}.
	                 Instead of writing the data out in binary
	                 format the user may pass the data to another
	                 processing routine. This would avoid having
	                 to make copies of the HDF formatted data set.

  sample_readpathP_f.f : A sample program written in Fortran that
		         shows how to access the data using a 
	                 Fortran program.

  creadpathP.c         : function written in C that returns the
		         data contained in the HDF file.

  fpreadpathP.c        : function written in F that returns the 
	                 data contained in the HDF file.
   				                  
  readpathp.pro        : Sample access program written in IDL.


  You can get compiled versions from:
     HREF"http://www-nsidc.colorado.edu/NASA/GUIDE/TOVS/apdxc.html

 
  Instructions for compiling programs:
  - Requirements:
	HDF libraries (Version 3.3). Source code or compiled 
        versions are available for most architectures from.
		 http://hdf.ncsa.uiuc.edu/obtain.html
	Ansi- C compatible C compiler if compiling C programs.
	Fortan 77 compiler for fortran programs.
	IDL, if using IDL based programs.
	
  - Edit the Makefile. Look for the switches for your architecture/
                       operating system. 


  - Check for Comments in the *.f source file. Some compilers define
    record lengths in either bytes or longwords. You may have to 
    modify the source accordingly.

  - Run Make:
	make unpack                   To compile unpack program
	make sample_readpathP_f       To compile sample fortan program
	make sample_readpathP_c       To compile sample C program.

  Note: Two files, LatGrid.exhdf and LonGrid.exhdf must reside in the 
        current working directory ($cwd)  when accessing the hdf data files. 
        LatGrid.exhdf contains the center latitude coordinate for each grid 
        cell and  LonGrid.exhdf contains the center longitude coordinate for
        each grid cell. If these files are not located in the current directory
        when using unpack_tovs, then the corresponding binary files containing
        the latitude and longitude coordinates of the TOVS Path-P grid cells
        generated by unpack_tovs will be filled with zero values. 

	The programs sample_*.c and sample*.f will not work properly without
        those files present. 

        The following error messages are sent to standard output during
        the execution of the unpack_tovs utility when LatGrid.exhdf and
        LonGrid.exhdf are inaccessible by the utility:

             HDF error: 
             Detected in HXIstaccess() [hextelt.c line 362]
             HDF error: 
             Detected in Hseek() [hfile.c line 1105]
             Error reading  SDS: LATITUDE_GRID
             HDF error: 
             Detected in Hseek() [hfile.c line 1105]
             HDF error: 
             Detected in HXIstaccess() [hextelt.c line 362]
             HDF error: 
             Detected in Hseek() [hfile.c line 1105]
             Error reading  SDS: LONGITUDE_GRID
             HDF error: 
             Detected in Hseek() [hfile.c line 1105]


      This is an inconvenience that will be fixed in the next version of
      that data set.