Ignoring terrain's effect on z-axis

[darwin]

I want a unit to act as a laser beam. I want to move him across the screen at a constant rate. This works fine except when he's going straight and then uphill...the laser moves forward then tilts upward at an angle and levels out...just like any flying unit would.

I want the laser to just go straight.

I think I could do the math if I knew his current flying height (which I do) and the height of the terrain at any given point. But I can't seem to find out what the height of a terrain point is... anyone know how to do that dynamically (i.e. during the game).

Darwin