Archaeology and GIS—The Linux Way
Although we were able to automate many of the tasks associated with survey work, we were never able to realize the full potential of the Linux/GRASS combination to automate virtually all of these tasks in concert with each other. We feel that a future project could be designed building on the work completed so far. This project could include equipping field crews with differentially corrected GPS receivers and data loggers to record and correct field data in real time. These data could then be downloaded at the end of the day and fed into the Postgres database engine which would provide seamless data entry and manipulation. Text formatting packages such as nroff/troff or LaTeX would be used to automate the production of site-specific reports and documentation. GNUplot could be used to produce the necessary graphs and charts. GRASS would be used for spatial display analysis.
Linked via scripts, we envision a time when field data collected in this manner could be downloaded, and within an hour, fully formatted and detailed site reports and maps would begin to pop out of the printer. Considering that with traditional methods the time gap between the input of raw data and the finished site-specific documentation is most often measured in weeks or months, we feel that this next level of integration is not only feasible, but advisable. By harnessing the tools Linux has made freely available, we believe there is much to offer researchers in this arena. We are glad to see development for both Linux and GRASS is so actively promoted by their respective communities and look forward to utilizing these tools to their fullest potential.
Although the project described above is of interest mainly to other archaeologists, the availability of a powerful GIS package for Linux is of interest to a larger segment of the Linux community, notably geographers, geologists and other researchers dealing with spatial data.
Development of GRASS languished for several years in the mid-90's after funding for future development at CERL came to a halt. There was concern among the international GIS community that GRASS, the father of raster analytical GIS packages, might finally be on its way to that great clippings bag in the sky. That fear was ended in November 1997 when the “GRASS Research Group” was established at Baylor University in Texas. This group pledged to continue development of GRASS. Interested in the ongoing maintenance and development of the GRASS GIS platform, they received the copyright for GRASS from CERL.
Coinciding with this renewed support for GRASS was the meteoric rise in the numbers of Linux GRASS users around the world, coupled with the availability of CPUs with sufficient speed to handle the volumes of data robust GIS package can deliver. The authors feel it has been the growth of the international Linux community that has been a major catalyst in giving GRASS a new lease on life. As Baylor continues to blaze new trails, a large audience of users eagerly awaits each update. Today, development is actively continuing, much of it pushed forward by users in the Linux community. Due to the stability, speed and power of Linux and its ability to turn even a modest PC into a strong UNIX workstation, GRASS has found a place in the Linux user community.
Since 1998, Linux GRASS has been developed by Markus Neteler, and the code is freely available at http://www.geog.uni-hannover.de/grass/ and several mirror sites. Additional UNIX flavors of GRASS are available from this site. Monthly updates of the GRASS 4.2.1 packages are published out of Hannover. Beside error corrections, these updates include new modules from independent GRASS programmers that have been collected from the international community and integrated into the system package.
GRASS was the last major GIS package to be completely command-line driven. A recent major improvement in GRASS has been the creation of a platform-independent graphical user interface based on the freely distributed Tcl/Tk libraries. The main work for this undertaking has been by Jacques Bouchard in France. This interface, TCLTKGRASS, gives users a clean GUI interface for GRASS commands and modules, as well as access through the standard command line. This GUI compliments the key strength of GRASS—it operates at the system level, allowing users to utilize the full suite of Linux utilities in conjunction with GRASS.
The current release of GRASS 4.2.1 now comes with more than 350 modules. In addition to standard GIS functions for raster, vector and point data, it offers statistical and image processing capabilities. Markus has recently written an algorithm, called “spectral mixture analysis”, that performs sub-pixel analysis and true coverage degrees in percent. Figure 3 shows the results from a module for GRASS that allows the user to perform sub-pixel analysis on vegetation and soil types with the spectral mixture analysis module. The left map shows the covered soils in percent. The right map shows the difference between a remotely sensed image and ground-truthed imagery. Black indicates no difference, red indicates high difference. Known field errors account for the red in the middle. This module can be used for geological analysis as well as detection of minerals based on their spectra. The vector lines in this image were created using the module r.line on the remotely sensed image, which was much faster than digitizing. This figure was created using xfig, a free drawing tool with good map scale features. xfig is supported in GRASS through a vector and raster exporting module. GRASS users can also rectify off-nadir aerial images taken with a hand-held camera from a small plane and convert them into quasi-orthophotos usable for area or distance calculations or mapping purposes. An overview of Linux GRASS, the tutorials and sample data are also available from Markus's University of Hannover, Germany, web site at www.geog.uni-hannover.de/grass/welcome.html.
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