Built-in Ids
// These identifiers are built in to POV-Ray, ready to use
// #declare pi = 3.1415926535897932384626
// #declare true = 1
// #declare yes = 1
// #declare on = 1
// #declare false = 0
// #declare no = 0
// #declare off = 0
// #declare u = <1,0>
// #declare v = <0,1>
// #declare x = <1,0,0>
// #declare y = <0,1,0>
// #declare z = <0,0,1>
// #declare t = <0,0,0,1>
// Other built in identifiers with no fixed values are
/*
clock // current clock value in animations (0..1)
clock_delta // clock step between frames
version // version (default 3.5, can be changed with #version)
initial_clock // start clock value (+KIn.n)
final_clock // end clock value (+KFn.n)
initial_frame // start frame number (+KFIn.n)
final_frame // end frame number (+KFFn.n)
frame_number // current frame number
clock_on // 1(true) if animation
image_width // width of current render
image_height // height of current render
*/