How to determine in which quadrant pt2 is relative to pt1

[gsc]

Hi,

 

How can I determine in which quadrant pt2 is relative to pt1?

 

[Tharwat]

Hi,

 

You can identify that with the angle value between the two points, so if angle is bigger than 180 and smaller than 270 then you are there.

[Aftertouch]

Or a X-Y compair.

 

+X +Y = 1st

+X -Y = second

-X -Y = third

-X +Y = fourth

[Grrr]

Heres something to investigate:

 

_$ (setq p1 '(10. 10. 10.))
(10.0 10.0 10.0)

_$ (setq p2 '(5. 13. -4.))
(5.0 13.0 -4.0)

_$ (setq p (mapcar '- p2 p1))
(-5.0 3.0 -14.0)

_$ (setq res (mapcar 'minusp p))
(T nil T)

_$ (setq res (apply '(lambda (a b c) (list a b)) res))
(T nil)

; +X +Y = 1st
; +X -Y = second
; -X -Y = third
; -X +Y = fourth
_$ (vl-some '(lambda (x) (if (equal (cdr x) res) (car x)))
 '(
   (1st nil nil)
   (2nd nil T)
   (3rd T T)
   (4th T nil)
 )
)
4TH

 

Or just use the angle function for the p1 and p2, and determine with cond if its between 0/90/180/270.

[gsc]

Ahhh of course...stupido! thx

[lrm]

Or...

 

(setq q (fix (+  1 (/ (angle p1 p2) (/ pi 2)))))

[Lee Mac]

Another -

(defun quadrant ( bpt pnt )
   (vl-position (mapcar 'minusp (mapcar '- pnt bpt '(0 0))) '(() (nil nil) (t nil) (t t) (nil t)))
)

[Grrr]

Another -

...

 

Very nice result, Lee! Added to my lib..

[gsc]

Thanx! Useful code

[gsc]

Hi, the codes of both Lee and Irm return q=3 where it should be q=4 for the folowing 2 coordinats...is this correct?

 

p1 (bpt) = 494487.36,5727352.41

p2 (pnt) = 494497.36,5725787.41

 

 

Modified: Sorry miscalculation...codes are correct

Edited May 14, 2018 by gsc