Dear GRASS’ers!
I wrote the shell-script <v.ldm> that computes “Linear Directional Mean” of the vector map (as explaned there http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/How_Linear_Directional_Mean_works/005p0000001r000000/) and displays LDM graphics on the X-monitor, optionally save it to vector line and update attribute table with LDM parameters.
Links:
https://raw.github.com/amuriy/GRASS-scripts/master/v.ldm
http://grass.osgeo.org/wiki/GRASS_AddOns#v.ldm
I hope it would be useful for somebody 