Detecting if a unit is not within line of sight of another unit??

Im making a sea map with key movement, and i have also invented (?) a wind system, so you move slower toward the wind, and much faster WITH the wind.

Now the problem i got is i want so there is no wind behind islands and trees. The "wind" is a unit that can be moved by special skills such as "control wind" so it looks like you can control the weather.

So i though that you cud check the wind-unit's line of sight, and all units in line of sight would be affected. I know how to change the units line of sight to unlimited (i think:)) but i cant seem to find "pick every unit in line of sight of unit".

Any help?



And if that is not a possible option, is there anyway to make a triangular region? Or a region with 4 dots that does NOT form a rektangle? In that case i can check between points in the line of sight of that unit and that way create a region that IS the wind-unit's line of sight.