I am trying to calculate the optimal route from one archaeological site to multiple sites. I already have the r.cost raster. My question is if I can use r.drain to multiple destination points.
The GRASS GIS 6.4 r.drain manual page shows:
coordinate=x,y[,x,y,...] Map coordinates of starting point(s) (E,N)
so just enter your coordinates as:
r.drain coordinate=x1,y1,x2,y2,x3,y3 ...
or you can save the coordinates as a vector and use parameter vector_points. These parameters are renamed in GRASS 7, check the manual.