[Back] [Forward] [Contents] [Home]


1 – GRASS is a free, open-source GIS. It was initially developed by the Construction Engineering Research Laboratory (CERL) of the US Army Corps in the early 1980s as a tool designed to manage military installations in the Fort Hood area in Texas (Lozar and Goran 1987; Westervelt 1988). Since the original development was funded with federal dollars, GRASS was realeased into the public domain as freeware. Today GRASS is an international open-source development project with its hub in Germany. It remains a free GIS, released under the Gnu Public License (Neteler and Mitasova 2002). GRASS is still used by many academic, commercial and governmental organisations around the world. GRASS was used early for archaeological applications (Madry and Crumley 1990; Farley et al. 1990; Gaffney and Stančić 1991) and continues to be popular in the discipline (Fisher et al. 1997; Brandon et al. 1999; Glass et al. 1999; Woodman 2000). A crucial enhancement for viewshed studies has been the development of a specialised module tailored for archaeological applications (Lake et al. 1998). This module automates Cumulative Viewshed Analysis (CVA), vastly reducing the human labour involved. GRASS software and documentation can be downloaded from the central web page.

2 – Some of the viewsheds feature 'tiger-stripe' effects at the edges of contiguous areas of visibility. This is due to subtle artefacts in the DEM resulting from a combination of the coarse level of contour information in the source maps and the interpolation algorithm used (nearest neighbour).

3 – Except Măgura, the largest tell in the study area. To calculate visibility from the base of this tell, the mound was removed by directly editing the surface model.

4 – For the viewshed analysis the r.cva module written by Mark Lake was used (Lake et al. 1998), in order to overcome the limitations of the standard GRASS viewshed module, r.los, which truncates the viewer height to its integer value. Postscript: as of GRASS version 5.0.3 r.los is updated to floating point operation.

5 – Accepting that in flat topographies people place emphasis on subtle features, see Hall and Coles 1994, 10

[Back] [Forward] [Contents] [Home]

© Internet Archaeology URL: http://intarch.ac.uk/journal/issue16/7/notes.html
Last updated: Thur Nov 11 2004