collision detection in grid

[kemalenver]

Hi,
 i'm making a simulation that uses a grid.  So far I have implemented path finding, taking into consideration only terrain.  I need to be able to take into account other objects such as the characters however (problem is they arent necessarily in the same place they were when i check).  Do I need to create masks for my characters? or is there an easier way of doing it because I am using a grid?  Thanks for any help.

[JuddMan]

if you're worried about how long it would take to calculate the unit's path often enough for it to go around a moving object, you could do it in 2 stages. (this being just imho)

first calculate the terrain waypoints for the journey, then do a calculation every second or so between the units current location and the next waypoint.

0.5 - 1 second is probably short enough... the warcaft peons sometimes paused while walking if there was a lot of them trying to make their way to and from the gold mines.