[GRASS-user] How to estimate viewable area from the top of tha mountain...

[sgw00412 at nifty.com]

Dear grass user

I'm looking for a grass command that unobstructed view area at one station.

For example...
I want to estimate the veiwable area around the top, when I am in the top of a
 mountain. It looks like simple, but I cannot see the opponent if there is a b
arrier in front of my position.

In bird survey ( bird count in fixed station ), investigator's observation are
a (or viewable area) is very important....

Is there a grass command that calcurates viewable area, when altitude dem (ras
t) and the observation point (vect or rast) are given ...?

Best

Yasuo shimada ( Japan weather Association )