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----------------  S G P   -   C   -   L I B R A R Y ----------------
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Table of Contents
-----------------

1. Legal Information
2. Brief Description
    2.1  SGP, SGP4/SDP4 and SGP8/SDP8
    2.2  This SGP-C-Library
    2.3  References
3. Source Code Availability
4. This C Release
    4.1  Files
5. Interface
6. Release Notes



1. LEGAL INFORMATION
====================

This library and this documentation is free software; you can 
redistribute it and/or modify it under the terms of the GNU 
Lesser General Public License as published by the Free Software 
Foundation; either version 2.1 of the License, or (at your option) 
any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public 
License along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA



2. BRIEF DESCRIPTION
====================

2.1 SGP, SGP4/SDP4 and SGP8/SDP8
--------------------------------
The SGP4 and SDP4 orbital models have become the most-used prediction
algorithms. The two-line orbital elements (TLEs) available from NASA's
Orbital Interest Group are based on these models, and in order to
obtain accurate predictions it is necessary to use the same model as
was used to generate the orbital elements data.

The SGP model is a faster but less accurate model which was used prior
to SGP4/SDP4, and the SGP8 and SDP8 models are faster and include some
improvements, but since NORAD has not yet adopted these these models
are not as reliable as the SGP4/SDP4 models are.

For more details on these orbital models see the Spacetrack Report
No. 3, which is available at http://www.celestrak.com.


2.2 This SGP-C library
----------------------
Based on Dr TS Kelso SGP4/SDP4 Pascal Library Package (available at
http://www.celestrak.com) I have developed an implementation of the
SGP, SGP4/SDP4 and SGP8/SDP8 models in C. There are probably still
some minor flaws in this source code, so please check 
http://www.brodo.de/english/pub/sgp/ 
for updates. 


2.3 References
--------------
For more information, take a look at the Spacetrack Report No. 3
available at http://www.celestrak.com

Additionally, the documentation included in Dr TS Kelso's SGP4-Pascal
Library offers a more detailed description of the SGP4/SDP4
models. This package is also available at http://www.celestrak.com



3. SOURCE CODE AVAILABILITY
===========================

Included in the Spacetrack Report No. 3 is a sample implementation in
FORTRAN. You can find the Spacetrack Report No.3 at
http://www.celestrak.com

Dr TS Kelso has written a SGP4/SDP4 Pascal Library Package which is
also available at http://www.celestrak.com

Based in this package I have written an implementation in C which is
available at 
http://www.brodo.de/english/pub/sgp/
Please check for updates often during the next weeks, since the C
package probably has some bugs. 



4. THIS C RELEASE
=================

When "INLINE" is not externally defined the source code should be
clean, plain ANSI which any C compiler should be able to work with. If
you find any problems, please report them to the maintainer Dominik
Brodowski at mail@brodo.de. Thank you!


4.1 Files
---------

DOCUMENTATION      - this Documentation
COPYING            - The GNU Public Library
sgp.h		   - header file for the sgp-c-library. Include this
		     file when accessing any of the included
		     prediction models
sgp_int.h	   - internal header file. You do not need to include
		     this header in your user program.
sgp_conv.c	   - functions needed to transform TLEs from ascii- to
		     binary format.
sgp_math.c	   - a few math helper functions
sgp_time.c	   - conversions between julian dates and "normal"
		     dates
sgp_deep.c	   - Deep Space subroutines for SDP4 and SDP8
sgp0.c		   - the SGP model
sgp4sdp4.c	   - the SGP4 and SDP4 models
sgp8sdp8.c	   - the SGP8 and SDP8 models
testing.c	   - Testing routine (for sample test data)
testdata	   - Sample test data (see Spacetrack Report No. 3)



5. INTERFACE
============

To access the sgp, sgp4/sdp4 and sgp8/sdp8 functions you need to
include the header file sgp.h. In this file you can find comments
which explain the in- and output, and the differences between the
various functions.



6. RELEASE NOTES
================

20020319	-	first release
20031230	-	fix for 69 or 70 chars wide testdata input file
20050321	-	fix off-by-ten multiplication in sdp8
			fix actan->atan2 replacement
			[both reported by Christopher Moore]


========================================================

Rosenheim, Germany, on March 21th, 2005

Dominik Brodowski
