Angle between three points

Hello all

Is there any way to calculate the angle between three
points, ///r to dimangular vertex option.

Thanks in advance.
Sri

 

Maybe two calls to the Utility object's AngleFromXAxis method and some
arithmetic.

 

here is a lisp that will return the angle enclosed between three points, where ip is the intersecting point and pt1 and pt2 are the other points:
Here is the code:

Code:

(defun enclAngle(pt1 pt2 ip / dist1 dist2 dist3)
(setq dist1 (distance pt1 ip)
dist2 (distance pt2 ip)
dist3 (distance pt1 pt2)
);setq
;; angle = acos((a^2 + b^2 - c^2) / (2*a*b))
(acos (/ (- (+ (sqr dist1) (sqr dist2)) (sqr dist3)) (* 2 dist1 dist2)))
);enclAngle



;;; acos returns the inverse of a cosine
;;; acos(X) = atan(-X / sqrt(-X*X+1)) + 2*atan(1)
(defun acos(value)
(+
(atan (/	(- 0 value)	(sqrt (+ (* (- 0 value) value) 1))))
(* 2 (atan 1))
);+
);acos

;;;not sure if sqr is built in
(defun sqr(num)
(* num num)
);sqr

 

There is a easy way , the old reliable CAL command

(if (= cal nil)
(arxload "geomcal")
)
;; just to chek if GEOMCAL is loaded

(Setq encAngle (c:cal "ang(apex,p1,p2)"));_ the angle included in p1 p2 with
intersection point as apex


Just a KISS: keep it simple .....Sir

Gabriel

 

now where's the fun in that?

 

i think it only fair to point out that instead of:
(c:cal "expression")
you can use
(cal "expression")
hence saving you an additional two key strokes
lol

 

Thanks all.

 

This should do it (I leave the testing to you):
The function TPA should return the angle in radians between the three points
(cp is the common point).


Private Function TPA(p1 As Variant, p2 As Variant, cp As Variant) As Double
TPA = Gang(gDX(p1, cp), gDY(p1, cp)) + Gang(gDX(p2, cp), gDY(p2, cp))
End Function

Private Function gDX(pa As Variant, pb As Variant) As Double
gDX = Abs(pb(0) - pa(0))
End Function

Private Function gDY(pa As Variant, pb As Variant) As Double
gDY = Abs(pb(1) - pa(1))
End Function

Private Function Gang(DX As Double, DY As Double) As Double
If DY = 0 Then Gang = 0 Else Gang = Atn(DY / DX)
End Function

 

Sorry, last function should be:

Private Function Gang(DX As Double, DY As Double) As Double
If DX = 0 Then Gang = 0 Else Gang = Atn(DY / DX)
End Function