Rotating ElevationGrid

; Rotating ElevationGrid about its center
; By Andy Yeh
CS RESET
TRANSFORM ; create an empty transform node
MAKE "elegrid OBJECT ; create a variable :elegrid with value the current object id.
FD 4.5 WEST 4.5 ; move the turtle so the elevationgrid will have 0,0,0 as center
ELEGRID ; create a random 10x10 ElevationGrid to the right and back of the turtle
MOVE OBJECT :elegrid
; whenever there is an object created, the keyword object will store its id.
; :elegrid will be used later for animation
MAKE "key [] ; make a variable :key as an empty list
MAKE "orilist [] ; make a variable :orilist as an empty list
; collect key values. Keys should be between 0 to 1
; I want to make 5 values as [0 0.25 0.5 0.75 1] in the key list
; I can certainly type in make "key [0 0.25 0.5 0.75 1] but I like using
; repeat to collect value because sometimes I need more values between 0 and 1
; the keys can be different intervals.
QUEUE "key 0 ; queue first value in key list
QUEUE "orilist ORI ; queue first value of current orientation
REPEAT 4 [ ; use repeat to collect the next 4 values.
QUEUE "key REPCOUNT / 4  ; queue is a command to add a value to the end of the list
RT 90
QUEUE "orilist ORI
]
; for animation, a timesensor is needed. The syntax of timesensor is
; timesensor name loop_interval_in_second loop_true_or_false
TIMESENSOR "ts 10 "true
; to animate orientation, we need an orientation interpolator
; oriint name key value
ORIENTATIONINTERPOLATOR "oi :key :orilist
; now we have everything
; we use command route to hook up everything
; route name from_node from_field to_node to_field
ROUTE "route1 "ts "fraction_changed "oi "set_fraction
; the above, we use the timesensor to drive orientationinterpolator
; the fraction_changed and set_fraction are fixed, simply type in exactly as they are.
ROUTE "route2 "oi "value_changed :elegrid "rotation
; value_changed is also a fixed term, which has to be exactly as it is.