[GRASS-user] CVA installation

[gary]

http://www.uni-kiel.de/ufg/ufg_BerDucke.htm
Can anyone provide some tips on installing CVA from this page. I have 
GEM installed. Here is my feeble attempt:
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linux:/usr/localsrc/grass61cvs/extman/gem-1.0.rc5 # ./gem
--install=/usr/localsrc/grass61cvs/cva/AdvancedViewshedAnalysis.tar.gz
--grass=/usr/localsrc/grass61cvs/grass-6.1.cvs_src_snapshot_2006_06_18
Uncompressing files...DONE.
Checking extension...DONE.

WARNING: GRASS version unknown. Extension might not work after
installation.
Configuring...DONE.
Segmentation fault
linux:/usr/localsrc/grass61cvs/extman/gem-1.0.rc5 # ./gem
--install=/usr/localsrc/grass61cvs/cva/AdvancedViewshedAnalysis.tar.gz
--grass=/usr/localsrc/grass61cvs/grass-6.1.cvs_src_snapshot_2006_06_18
Uncompressing files...DONE.
Checking extension...DONE.

WARNING: GRASS version unknown. Extension might not work after
installation.
Configuring...DONE.
Segmentation fault