Check if points is Line

Could you help me how and which is fastest to check if multi point is lie in Line (all direction)?. I just think idea calculate k with x,y, and check loop three point as pair, but it might too slow

(sorry for my bad English)

Hi ,

Select a line and the routine would select all points that lie on the selected line .

(defun c:test (/ e ent lst i ss ents)
 ;; Tharwat 13. 07. 2011
 (if
   (and
     (setq e (car (entsel "\n Select a Line :")))
     (eq (cdr (assoc 0 (setq ent (entget e)))) "LINE")
   )
    (progn
      (setq
        lst (ssget "_f"
                   (list (cdr (assoc 10 ent)) (cdr (assoc 11 ent)))
            )
      )
      (repeat (setq i (sslength lst))
        (setq ss (ssname lst (setq i (1- i))))
        (setq ents (entget ss))
        (if (not (eq (cdr (assoc 0 ents)) "POINT"))
          (ssdel ss lst)
        )
      )
    )
    (princ)
 )
 (if lst
   (sssetfirst
     nil
     lst
   )
 )
 (princ)
)

Tharwat

;;;++++++++++ 3D Is Point On Line ++++++++++++++++++++++++++++++++++++++
;;;ARG -> TestPt LinePt1 LinePt2 Fuzz
;;;RET T nil
(defun is_pt_online (pt l1 l2 fz)
 (equal (distance l1 l2)
        (+ (distance l1 pt)
           (distance l2 pt)) fz))

-David

Geometric Functions

Thanks all and nice to be helped ^^

@tharwat : sorry for my Bad English, so it harder and harder to me to described, it can make misunderstanding ^^ I have no Point object, just a point to check

@David : it like to check in a segment. How about if pt is still on line, but it out of l1 l2 (extend of l1-l2)? so, i will add more cond ^^

@LeeMac : oh, just say thanks and copy. I like LM:ListCollinear-p but it more difficult to understand (to me ^^)

;;;Are Points CoLinear
;;;ARG -> 3 Points and Fuzz
;;;RET -> T nil
(defun is_pt_colinear (p1 p2 p3 fz)
 (or (equal (distance p1 p3)
            (+ (distance p1 p2)
               (distance p2 p3)) fz)
     (equal (distance p1 p2)
            (+ (distance p1 p3)
               (distance p3 p2)) fz)
     (equal (distance p2 p3)
            (+ (distance p1 p2)
               (distance p1 p3)) fz)))

-David

@LeeMac : oh, just say thanks and copy. I like LM:ListCollinear-p but it more difficult to understand (to me ^^)

You're welcome.

A quick explanation of my collinear predicate functions: LM:Collinear-p uses the triangle inequality to test the collinearity of three points, LM:ListCollinear-p uses the fact that the vector dot product between two collinear unit vectors will equal +/- 1.

You're welcome.

 

A quick explanation of my collinear predicate functions: LM:Collinear-p uses the triangle inequality to test the collinearity of three points, LM:ListCollinear-p uses the fact that the vector dot product between two collinear unit vectors will equal +/- 1.

Tks Lee ^^ (link is so useful)

Ah, i have just wrote a more simple (to me) collinear, but i don't sure it's going right. Please recommend to help me

(defun ST:Geo-Linear (p1 p2 p3 fuzz)
((lambda ( a b )
   (or
       (equal (abs (- a b)) pi fuzz)
       (equal (abs (- a b)) 0 fuzz)
   )
   )
   (angle p1 p2)(angle p1 p3)
))

(defun ST:Geo-ListLinear (lst / tmp)
(setq i 2)
(cond ((and (= (length lst) 3)(ST:Geo-Linear(car lst)(cadr lst)(caddr lst) 1e-)(setq tmp T))
       (T (while (and (< i (1- (length lst)))
               (setq tmp (ST:Geo-Linear (nth 0 lst)(nth 1 lst) (nth (setq i (1+ i)) lst) 1e-))
               tmp
           )
       )
)
tmp
)

Cause function will stop immediately when it find out three point not "in Line", so i think it a bit more quickly

The angle function will measure angles from the X-axis of the UCS plane.

The angle function will measure angles from the X-axis of the UCS plane.

I thinked about it, but i guess (not sure) it may not problem if only compare angle.If it linear, when X-axis change, subtract of 3 point in Line still eq 0 or pi (i'm not sure).

I thinked about it, but i guess (not sure) it may not problem if only compare angle.If it linear, when X-axis change, subtract of 3 point in Line still eq 0 or pi (i'm not sure).

Set your UCS to World and try:

(ST:Geo-Linear '(1.0 1.0 1.0) '(2.0 2.0 4.0) '(3.0 3.0 3.0))

Cause function will stop immediately when it find out three point not "in Line", so i think it a bit more quickly

If you study my function a little closer you will notice that the recursive call will not be reached if any three points are not collinear.

Other way to skin a cat

(defun c:point@line (/AUX-PT E E-OBJ ENT PT PT-XYZ   )
 ;; Tharwat 13. 07. 2011
 ;; add by DEVITG 

(VL-LOAD-COM)
 (if
   (and
     (setq e (car (entsel "\n Select a Line :")))
     (eq (cdr (assoc 0 (setq ent (entget e)))) "LINE")
    (setq pt (car (entsel "\n Select a point :")))
    (eq (cdr (assoc 0 (setq ent (entget pt)))) "POINT")
   );_and
(progn
(setq e-obj (vlax-ename->vla-object e))
(setq pt-xyz (cdr (assoc 10 (setq ent (entget pt)))))

(setq aux-pt (vlax-curve-getclosestpointto e-obj pt-xyz t))

(if (equal aux-pt pt-xyz)
 (alert "point belong to line")
   (alert "point is out the  line")
)
     
);_ progn
   );_ if 
   
);_ end defun

Set your UCS to World and try:

 

(ST:Geo-Linear '(1.0 1.0 1.0) '(2.0 2.0 4.0) '(3.0 3.0 3.0))

 

If you study my function a little closer you will notice that the recursive call will not be reached if any three points are not collinear.

Oh, now i understand ^^ It don't look in Z coord ^^ So i will return distance..

In your listcollinear, it use "recursive", and i not good in this case.Hihi..

I still have to study more and more. Thank you so much . Have a good day

Thank you so much . Have a good day

You're welcome, you too