Use the
createVehicle command.
You don't need a
z dimension for objects that will be on the ground. Also note Spooner's comment: if the created object collides with another, the game engine will place it somewhere nearby.
Have a go with the following:
Start creating a new mission in the mission editor.
Place yourself as a soldier named
dude.
Create a trigger, activated by Radio Alpha, repeatedly, and write the following in the On Activation line:
[] exec "barrel_square.sqs"
_firstbarrel = "Barrel1" createVehicle [(getPos dude select 0) - 5, (getPos dude select 1) - 5]
_secondbarrel = "Barrel1" createVehicle [(getPos dude select 0) - 5, (getPos dude select 1) + 5]
_thirdbarrel = "Barrel1" createVehicle [(getPos dude select 0) + 5, (getPos dude select 1) - 5]
_fourthbarrel = "Barrel1" createVehicle [(getPos dude select 0) + 5, (getPos dude select 1) + 5]
exit
Preview the mission. Every time you call Radio Alpha, you will find yourself in the centre of a ten-metre square marked by barrels.
P.S. Are you sure this is related to OFP, because I don't quite understand your
other question? Are the two topics somehow related?