How to know a point is on an arc?

I’ve got many points and an arc. I need to know which points are sitting on the arc. Any suggestion?

 

u can use the vlax-curve functions, and it will work for lines arcs
polylines circles etc

on the arc. Any suggestion?

 

Here's one, along with a sample on it's use, that will work for any arc,
line, pline, spline, ellipse....

(defun pt-on-arc? (pt arc)
(if (= (type arc) 'ENAME)
(setq arc (vlax-ename->vla-object arc))
)
(if (vlax-curve-getparamatpoint arc pt)
t
nil
)
)

(defun c:test (/ arc pt)
(setq arc (car (entsel "\nSelect arc: "))
pt (getpoint "\nSelect point: ")
)
(if (pt-on-arc? pt arc)
(princ " Yup...")
(princ " Nope...")
)
(princ)
)

 

Didn't know that Luis, thanks.

Which could reduce Jeff's function to

(vlax-curve-getparamatpoint object point)

which seems hardly worth a wrapper to get a
T or NIL return value. I'd just use the return
value(s) from vlax-curve-xxxx, or perhaps
numberp if T or NIL is really needed.


PS: Where in the help files does it say that?

 

Heh, learn something new everyday.
This also is the case in 2002.
I don't recall seeing that mentioned before, thanks Luis!

 

FWIW, my help file doesn't mention it (or at least
not that I can find at the moment)

 

There is another way with ActiveX method:

(vl-load-com)

(defun COINTSONCURVE? ( / )
(setvar "CMDECHO" 0)

(setq vobj
(vlax-ename->vla-object
(car (entsel "\nSelect a curve (an arc) :"))))
(setq lst nil)
(while (setq pt (getpoint "\nPick point : "))
(setq lst (cons pt lst)))
(setq arc_lst (vl-remove-if (function not)
(mapcar (function (lambda (x)
(if (vlax-curve-getparamatpoint vobj x) x))) lst)))
(if arc_lst
(princ (strcat "There are is "
(itoa (length arc_lst))
" points on curve"))
(princ "There aren't points on curve")))

(COINTSONCURVE?)

 

Well, thanks for mentioning it.