Accessing Civil 3D objects with autolisp

I have been working with the Civil 3D 2010 API in visual lisp recently, and I thought I would share an example of working with an alignment object. This example has plenty of comments, but basically it shows you how to find a point near the alignment based on a station and offset. Then it does the opposite and shows you how to determine the station and offset, given a point. For clarity, I have left out most of the error checking.

; standard entity selection
(setq sel (entsel "\nSelect Alignment: "))
; get the entity name
(setq ent (car sel))
; get the entity list
(setq lst (entget ent))
; check to make sure the selection was the expected type
(if (eq "AECC_ALIGNMENT" (cdr (assoc 0 lst)))
  ; if so, convert the entity into a VLA-OBJECT
  (setq obj (vlax-ename->vla-object ent))
)
(if obj
  (progn
    ; get the name of the alignment
    (setq nam (vlax-get-property obj 'Name))
    ; get the start station
    (setq sta1 (vlax-get-property obj 'StartingStation))
    ; get the end station
    (setq sta2 (vlax-get-property obj 'EndingStation))
    ; set a couple of variables
    (setq sta 100.0 off 10.0)
    ; using the above variables, find this point on the alignment
    (vlax-invoke-method obj 'PointLocation sta off 'x 'y)
    ; create an AutoCAD point at this location
    (entmake (list (cons 0 "POINT")(cons 10 (list x y))))
    ; ask the user to pick a point
    (setq pt1 (getpoint "\nSelect point: "))
    ; find the station and offset for this point
    (vlax-invoke-method obj 'StationOffset (car pt1) (cadr pt1) 'sta 'off)
    ; inform the user
    (alert (strcat
            "The station is "
            (rtos sta 2 2)
            "\nThe offset is "
            (rtos off 2 2)))
  )
)