$Id$

The following is excerpted from the GPSTk web/wiki site at 
http://www.gpstk.org/.

The website includes a variety of additional and the latest information 
including:
   * Source code and compiled binaries
   * Coding examples
   * Doxygen documentation
   * System requirements and build instructions
   * A users guide
   * Publications
   * Email lists
   * Support question/answer
   * Development process (including feature suggestions, bug tracking, 
      schedule, testing, and developer documentation)
   * Source code repository information
   * GPSTk IRC channel
   * Success stories

What is GPSTk?
--------------

The goal of the GPSTk project is to provide an open source library and suite
of applications to the satellite navigation community--to free researchers
to focus on research, not lower level coding.

GPS users employ practically every computational architecture and operating 
system. Therefore the design of the GPSTk suite is as platform-independent as 
possible. Platform independence is achieved through use of the ANSI-standard 
C++ programming language. The principles of object-oriented programming are 
used throughout the GPSTk code base in order to ensure that the code is 
modular, extensible, and maintainable.

The GPSTk suite consists of a core library, auxiliary libraries, and a set 
of applications. The GPSTk provides a wide array of functions that solve 
processing problems associated with GPS such as processing or using standard 
formats such as RINEX. The libraries are the basis for the more advanced 
applications distributed as part of the GPSTk suite.

The GPSTk is sponsored by Space and Geophysics Laboratory, within the Applied 
Research Laboratories at the University of Texas at Austin (ARL:UT). GPSTk is
the by-product of GPS research conducted at ARL:UT since before the first 
satellite launched in 1978; it is the combined effort of many software 
engineers and scientists. In 2003 the research staff at ARL:UT decided to 
open source much of their basic GPS processing software as the GPSTk.


GPSTk Core Library
------------------

The GPSTk core library consist of the most robust, broadly useful,  and 
platform independent code in the GPSTk.  It provides a number of models and 
algorithms found in GPS textbooks and classic papers, such as solving for 
the user position or estimating atmospheric refraction. Common formats 
are supported as well, such as RINEX or SP3. There are several categories 
of functions in the GPSTk library:

   1. GPS time. Conversion among time representations such as MJD, GPS week 
      and seconds of week, and many others.

   2. Ephemeris calculations. Position and clock interpolation for both
      broadcast and precise ephemerides.

   3. Atmospheric delay models. Includes ionosphere and troposphere models.

   4. Position solution. Includes an implementation of a Receiver Autonomous 
      Integrity Monitoring algorithm.

   5. Mathematics. Includes Matrix and Vector implementations, as well as
      interpolation and numerical integration.

   6. GNSS data structures. Data structures that contain observations mapped
      according to epochs, satellites, sources and types of observations.
      Appropriate processing classes are also provided, including a complete
      'Precise Point Positioning' (PPP) processing chain.

   7. Application framework. Includes processing command lines options,
      providing interactive help and working with file systems.

A more detailed description of the functionality provided by the GPSTk library 
can be found in the Doxygen documentation on the GPSTk website.

The GPSTk Core Library and its associated test programs can be built 
independently of building the GPSTk Applications or Auxiliary Libraries.
The GPSTk Core Library source code contains no dependencies outside of the
GPSTk Core Library and Standard C++ and will build cleanly on all 
supported platforms.


GPSTk Auxiliary Libraries
-------------------------
The auxiliary libraries contains code that could be useful in GNSS processing 
but do not fit this description and portability of the core library. This code
could contain highly specialized algorithms or be related to the message 
format of a specific receiver. The code could require libraries or system 
functions that are broadly available but not part of the C++ standard.  
Currently the auxiliary libraries are:

   1. rxio - Receiver and input/output library
   2. vplot - Vector graphics library
   3. geomatics - Precise positioning library
   4. procframe - Framework for storage, filtering and processing of
                  observations, including 'PPP' processing.

GPSTk Applications
------------------

The libraries are the foundation for applications within the GPSTk suite.  
The applications support greater depth of functionality to support research 
and development. The applications are almost entirely console based (i.e., 
without a graphical user interface). They can be grouped functionally into 
a number of categories.

   1. RINEX utilities - The RINEX utilities provide a set of applications 
      that can be used to examine, manipulate, and plot RINEX observation 
      files.

   2. Positioning - The positioning applications include two different 
      applications that perform standard pseudorange-based positioning and 
      two that implement differential phase-based solutions. 

   3. Residual analysis - A residual analysis application computes two types 
      of measurement residuals using a single receiver or two receivers in 
      a zero baseline configuration. 

   4. Ionospheric modeling - The ionospheric modeling applications utilize 
      the two frequency TEC estimate from the RINEX utilities and compute 
      a model of the ionosphere. 

   5. Signal Tracking Simulation - These utilities simulate the tracking 
      of GPS C/A and P-code.

   6. Basic transformations -  Conversions of time and coordinate systems.

   7. Observation data collection and conversion -  Translating receiver 
      specific data formats to RINEX.

   8. File comparison and validation - Differing observations files against 
     a truth source.

   9. Data editing - Simple editing like systematic removal of observations 
      by satellite, type or time and more advanced editing like cycle slip 
      detection and correction.

   10.Autonomous and relative positioning - Navigation and surveying 
      applications.


The GPSTk applications are dependent on the GPSTk libraries.  However, the 
GPSTk Applications may also contain external dependencies.  Some applications 
may not build or run successfully on all the supported platforms. 

License
-------

The source code provided by the GPSTk is distributed under the GNU LGPL 
(http://www.gnu.org/copyleft/lesser.html). This license gives all users the 
right to use and redistribute the code. Users of the GPSTk are not required 
to open their source, according to the LGPL. This makes the GPSTk a practical 
choice for commercial projects.


Credit
------

If you use the GPSTk to produce an article or thesis, please reference 
the following article to credit the GPSTk project.

Brian Tolman, R. Benjamin Harris, Tom Gaussiran, David Munton, Jon Little, 
Richard Mach, Scot Nelsen, Brent Renfro, ARL:UT; David Schlossberg, 
University of California Berkeley. "The GPS Toolkit -- Open Source GPS 
Software." Proceedings of the 17th International Technical Meeting of 
the Satellite Division of the Institute of Navigation (ION GNSS 2004). 
Long Beach, California. September 2004

For LaTeX users, here is a BibTeX entry for that citation.

http://www.gpstk.org/pub/Documentation/GPSTkPublications/gpstk-ion-gnss-2004.bib


Contact Info
------------
The GPSTk is a collaborative effort. However, you can email to 
gpstk@arlut.utexas.edu or contact one of the CoreTeam members
(http://www.gpstk.org/bin/view/Development/CoreTeam).