check c_trace in manual, and AUM 101 or 100 dealt with c_trace a lot... but anyway, it is the LiteC version, if temp is a VECTOR (if var, use 3 vars: vector(tempx,tempy,tempz) or something like this... ) :

my.z -= trace(my.x, temp , IGNORE_ME | IGNORE_SPRITES | IGNORE_MODELS | USE_BOX);