Trigger On The Ground

[LAPD]

How can I do a trigger which will be activated only if the unit is on the ground?

[Black_Feather]

I'd put this in the triggers condition field

getpos player select 2 < 1

[Trapper]

If you want to use the trigger's conditions togehter with the height limit:
this and (getpos player select 2) < 1
You can replace player by the name of any unit.

Or if your trigger has to be activated by any possible unit that passes on the ground try:
this and (getpos (thislist select 0) select 2) < 1           (just guessing)

[The-Architect]

Whatever you want to happen in the triger make it happen in a script. Name all your air units. Then make the script exit if any air units go through it. Or have it go back to the start of the script. Something like that.