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gpspoint12 is a program to get position, down- and up-load waypoints, routes and tracks form your GPS to your computer. Several Garmin devices are supported by gpspoint;

GPStrans13 is a program which allows for track, route, and waypoint data to be transferred to and from various Garmin GPS;

GPSBabel14 reads and writes GPS waypoints in a variety of formats. Backends include GPX, Magellan and Garmin serial protocols, Geo-caching.com, GPSMan, Garmin Mapsource, Magellan Mapsend, and many others. It runs on various operating systems.

GRASS itself provides two scripts: v.in.garmin.sh as well as s.in.garmin.sh (both require gpstrans). However, no checks are performed in these scripts for datum, projection and format of data. You must check by yourself that your receiver, gpstrans and GRASS use the same map datum and projection.


Figure 13.12. Screenshot of GRASS / UMN/MapServer demonstrational Web site as implemented at ITC-irst



13.4. WEBGIS APPLICATIONS WITH UMN/MapServer

An excellent, fast and flexible Open Source mapping Web software is UMN/MapServer. On a basic level, the program is run through CGI (Common Gateway Interface). Then it only requires a definition file and a HTML template (and GIS data of course) to respond to a variety of spatial requests like making maps, scale-bars, and point, area and feature queries. The installation is quite convenient as the configuration for the Web mapping interface can be done without any programming. For more complex applications, UMN/MapServer can be enhanced using Java, JavaScript, PHP or other Internet technologies. The MapScript extension which is based on PERL provides access to the underlying UMN/MapServer C API. Developers may add mapping functions to their PERL scripts. With MapScript also SHAPE files can be read or written. The UMN/MapServer software is freely available from the UMN/MapServer Web site.15 It can be extended with UMN/MapServer Applets16 to add menu icons into the map or other extended features which require JAVA.

In addition, with GDAL and OGR libraries (shipped with GDAL), UMN/MapServer reads common GIS raster and vector formats. When GDAL was compiled with libgrass support (GDAL/libgrass page17), UMN/MapServer directly reads raster data from a GRASS LOCATION through GDAL. With future releases of libgrass also vector and site data may become supported. Figure 13.12 provides a screenshot of the simple demonstrational GRASS / UMN/MapServer which is implemented at GRASS Web site.18

A more complex implementation using several Free Software tools is shown in Figure 13.13. Requirements for this implementation are: Web server such as Apache Server (with PHP), UMN/MapServer, GDAL/OGR, PROJ4, lib-grass, GRASS and PostgreSQL/PostGIS. At the time of writing this book there have been limitations to automatically color-resample those GRASS raster data which contain more than 256 colors. If you intend to directly read from GRASS locations, consider to rescale the map range to 8bit which is mostly sufficient for Web presentations (be sure not to use these maps in GIS computations!). The GRASS module for rescaling is r.rescale.

To read raster data directly from a GRASS LOCATION, you need, as mentioned above, the libgrass which is available on the GRASS Web site and CVS. This library reads the .grassrcS file for definition of LOCATION, MAPSET and GISDBASE (compare also Section 11.3). The file has to be stored in the $D0CUMENT R00T directory (might be the $HOME of the user-ID under which the local Web server is running). Due to GRASS permissions handling, the GRASS LOCATION data for UMN/MapServer have to be stored with the same user-ID as the Web server is running.




Figure 13.13. Sample UMN/MapServer implementation model

Two more files are required:

UMN/MapServer definition file: to be stored in a map-script directory in parallel to the htdocs/ directory (see sample in the Appendix C.1);

a HTML template file which goes into the HTML space (into htdocs/ directory, see sample in the Appendix C.2).

Additionally you may want to add further GIS data in different formats (remember to verify the data copyrights when publishing data online).

The minimum requirements for a UMN/MapServer implementation are a running Web server such as Apache, and appropriate access to the files. Once running, you may want to enrich the server with JAVA or PHP, numerous public mapservers are accessible on the Internet to get inspired.

NOTES

1 FreeGIS Project Web site, http: www.freegis.org

2 Maas river bank soil pollution data descriptions: gstat package documentation; Burrough and McDonnell, 1998:309-311 (subset)

3 Maas river bank soil data GRASS LOCATION,

http: grass.itc.it/statsgrass/ maas grass location.tar.gz

4 gstat software, http: www.gstat.org

5 gnuplot software, http: gnuplot.sourceforge.net

6 gstat examples, http: www.gstat.org/examples.html



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