Hello Yasuo,
If you just need to display line directions with an arrow head on
end-node, you can use the "display=dir" option available for d.vect.
If you need to display a custom symbol, you cannot use "icon=" option,
which is dedicated to point and centroid features (not lines).
Envethough the
Hollow grass users
I'm from Japan, and biggner.
I do not find how to draw line with arrow mark to line top (tip).
for exsample...
normally line;
line with arrow mark to line top (tip);
>
or
<
I read online manual and tried to command 'd.vect layer_name icon=basic/arro