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DGPS On a stationary GPS without a differential correction signal, you should see a 20 meter average radius "random walk" pattern. On the same receiver with DGPS corrections and a good view of the sky, the error should be reduced to approx. 2 meters average radius.

Earth3D Earth3D visualizes the earth in realtime in a 3D view. You can rotate and zoom the view until countries, cities and even single houses become visible (in areas where the necessary map resolution is available), and fly around. You can also embed external data like current earthquake positions or cloud data. Additional data layers can be added to the view, e.g. country flags and names. The package uses data from NASA, USGS, the CIA, and the city of Osnabrück. The data is loaded on demand over the Internet.

GDAL The Geospatial Data Abstraction Library (GDAL) is a unifying C/C++ API for accessing raster geospatial data, and currently includes formats like GeoTIFF, Erdas Imagine, Arc/Info Binary, CEOS, DTED, GXF, and SDTS. It is intended to provide efficient access, suitable for use in viewer applications, and also attempts to preserve coordinate systems and metadata. Python, C, and C++ interfaces are available.

GEOS 'GEOS' is a C++ implementation of the functions and predicates defined in the OpenGIS "Simple Features for SQL" specification. It includes high quality implementations of all important spatial relationships and operations, robust versions of all functions in the dimensionally extended 9 intersection predicate model, and implementations of the operators Buffer(), Union(), and Intersection() and all other SFSQL functions including Area(), Length(), Centroid(), etc.

GMT Generic Mapping Tools is a collection of ~60 GNU/Linux tools that allow users to manipulate (x,y) and (x,y,z) data sets (including filtering, trend fitting, gridding, projecting, etc.) to produce Encapsulated PostScript File (EPS) illustrations ranging from simple x-y plots through contour maps to artificially illuminated surfaces and 3-D perspective views in black and white, gray tone, hachure patterns, and 24-bit color. GMT supports 25 common map projections plus linear, log, and power scaling, and comes with support data such as coastlines, rivers, and political boundaries. Since the package is quite large, the authors suggest looking at the list of mirrors on the page to ensure that you download from the one closest to you.

GPSBabel 'GPSBabel' converts waypoint data between about four dozen file formats, including Magelland and Garmin serial, Mapsource, Mapsend, Streets & Trips, Delorme, National Geographics, many Pal formats, and many others. It is endian and word-size safe, includes a GUI, and runs on a variety of operating systems. It also supports Groundspeak GPX extensions for geocaching.

GPStk 'GPSTk' is a set of both fundamental and advanced GPS processing algorithms. The library provides functions including RINEX I/O, ephemeris calculation, atmospheric refraction models, and positioning algorithms. The applications include cycle slip detection and removal, calculation of the Total Electron Content (TEC) of the ionosphere, bindings to 'octave', and RINEX file manipulation.

GRASS (Geographic Resources Analysis Support System) Commonly referred to as GRASS, this is free Geographic Information System (GIS) software used for geospatial data management and analysis, image processing, graphics/maps production, spatial modeling, and visualization. GRASS is currently used in academic and commercial settings around the world, as well as by many governmental agencies and environmental consulting companies. GRASS is an official project of the Open Source Geospatial Foundation. GRASS contains modules for raster data manipulation (2D and 3D voxels), vector data manipulation, rendering images on the monitor or paper, multispectral image processing, point data management and general data management, as well as tools for interfacing with digitizers, scanners, and SQL databases as PostgreSQL, and other through an ODBC interface.

Gama GNU Gama is a project dedicated to adjustment of 'geodetic networks'. GNU Gama is based on a C++ library of geodetic classes and functions `libgama' and a small C++ template matrix library `matvec'. The stable branch of the project is limited to network adjustment in a local coordinate system and its functionality is represented by the program `gama-local, ' which adjusts geodetic (free) networks of observed distances, directions, angles, height differences, 3D vectors and observed coordinates (coordinates with given variance-covariance matrix). In the new branch the adjustment model is based on geocentric coordinate system (adjustment model on ellipsoid). Its functionality is represented by the program `gama-g3'.

Geo Weather Geo::Weather is a Perl module used to retrieve weather.com information based on city/state or US zip code. In order for the timeout code to work correctly, you must be using a recent version of libwww-perl and IO::Socket. Geo::Weather was developed with libwww-perl 5.53 and IO::Socket 1.26.

GeoToad 'GeoToad' is a geocaching query tool to help speed up choosing a cache and collecting the data. You can generate any kind of complex query you want, and the program will go and poll the Geocaching query, grab the data, and output it to any format you want. The info can be synced to various devices in over 20 different formats.

Gpsdrive 'Gpsdrive' is a map-based navigation system. It displays your position on a zoomable map provided from a NMEA-capable GPS receiver. The maps are autoselected for the best resolution, depending of your position, and the displayed image can be zoomed. Maps can be downloaded from the Internet with one mouse click. The program provides information about speed, direction, bearing, arrival time, actual position, and target position. Speech output is also available. All Garmin GPS receivers with a serial output should be usable, as well as other GPS receivers which support the NMEA protocol.

Harmonics

Height Map Generator Height Map Editor edits, generates, and manipulates terrain height maps. These can be used in terrain renderers, which are used in games, applications, and demos. The program itself is small (the entire distribution is smaller than 400 Kb) but it can work with maps up to 10000x10000. Features include 16 levels of zoom, the ability to sink, smooth, or rise the terrain, the ability to put your own objects (ie volcanos, rivers, mountains, craters, etc.) in/on/over existing terrain, multiple brush sizes, flood and tolerance based fills, and the ability to place a height over terrain and add to or excavate from terrain.

MapServer MapServer is a CGI based Web mapping application development tool. It processes user defined configuration files and templates to allow for a wide variety of applications to be developed, including interactive mapping, and spatial query definition and processing. It supports several data formats. Key features include scale dependent map rendering, automatic scalebar and legend building, feature labeling with collision avoidance, logical and thematic classifications, and on-the-fly projection of raster and vector data. The application can also access other WMS servers as a cascading map server.

PHP Weather PHP Weather makes it easy to show the current weather on your Web page. PHP Weather retrieves the latest METAR (weather) report and converts this format into both imperial and metric units, caches the data in a MySQL, PostgreSQL, or DBA database for fast retrieval, and makes it easily available in PHP scripts. You can display the data in several languages by using the included translations. You can also access the information with a WAP-enabled mobile phone.

PhpWX 'phpWX' displays current weather conditions. It can display up-to-date weather information, active advisories, and more, based on a Zip Code. It can also display windchill, heat index, and improved condition vars. Visitors on your site can enter their zipcode for their own weather conditions, too.

PostGIS PostGIS adds support for geographic objects to the PostgreSQL object-relational database. It "spatially enables" the PostgreSQL server so it can be used as a backend spatial database for geographic information systems (GIS).

QGIS Quantum GIS (QGIS) is a Geographic Information System (GIS) built for GNU/Linux. QGIS supports vector, raster, and database formats.

Snow Path Formation Simulator Snow Path Formation Simulator is a program that models the process of people forming very distinct, and yet not always altogether logical looking, paths in the snow as they walk across open spaces. The evolving condition of the snow is displayed graphically. This project may eventually mature into a screensaver.