Select Specific Entity Type AutoLisp

Question

When selecting a point is there a way to filter OSNAP to only snap onto a specific entity type and not an entity of another type. eg

Snap only to lines.

setq startpt (*SNAP FILTER CODE* "LINE" (getpoint "\nChoose Start Line : "))

Snap only to arcs.

setq startpt (*SNAP FILTER CODE* "ARC" (getpoint "\nChoose Start Arc: "))

Snap only to polyline.

setq startpt (*SNAP FILTER CODE* "POLYLINE" (getpoint "\nChoose Start Polyline: "))

I hope the fake lisp above helps in understanding what I'm trying to ask.

Thanks in advance.

Answer 1

The AutoLISP osnap function can be used to return a point snapped to geometry using a supplied Object Snap modifier, however, this function will not filter the candidate geometry.

Therefore, you could alternatively supply the point returned by getpoint as the point argument for a filtered ssget selection, or test the entity returned by the nentselp function.

Here is a possible solution using ssget:

(defun c:test1 ( / pnt )
    (while
        (and
            (setq pnt (getpoint "\nSelect start point on arc: "))
            (not (ssget pnt '((0 . "ARC"))))
        )
        (princ "\nThe point does not lie on an arc.")
    )
    (if pnt
        (princ (strcat "\nThe user picked (" (apply 'strcat (mapcar 'rtos pnt)) ")."))
        (princ "\nThe user did not supply a point.")
    )
    (princ)
)

Here is a possible solution using nentselp:

(defun c:test2 ( / ent pnt )
    (while
        (and (setq pnt (getpoint "\nSelect start point on arc: "))
            (not
                (and
                    (setq ent (car (nentselp pnt)))
                    (= "ARC" (cdr (assoc 0 (entget ent))))
                )
            )
        )
        (princ "\nThe point does not lie on an arc.")
    )
    (if pnt
        (princ (strcat "\nThe user picked (" (apply 'strcat (mapcar 'rtos pnt)) ")."))
        (princ "\nThe user did not supply a point.")
    )
    (princ)
)