Angle between 3D points (polyline vertices)
You are receiving wrong result since function angle works in 2d plane. To receive correct result you would have to change drawing plane. Also to work with 3d your points need three coordinates i.e '(0 0 0). Otherwise mapcar will cut of z coordinate.
If I understood your request you are looking for something like this.
To calculate angle between points you need two vectors between three points. If you have single vector between two points then we talk about vector angles, and you have three components.
So if situation from image is your case, we have three points, p1 = 0,0,0 p2 = 10,10,10 p3 = 20,0,0. To calculate angle between vectors v1 = p2-p1 and v2 = p2-p3 function is
(setq p1 '(0 0 0))
(setq p2 '(10 10 10))
(setq p3 '(20 0 0))
(setq v1 (mapcar '- p2 p1))
(setq v2 (mapcar '' p2 p3))(defun rad_to_deg (rad)(* 180.0 (/ rad pi)))
(defun angles_two_vect (v1 v2 / ang xa ya za xb yb zb acos asin)
(defun acos (x) (cond ((and(>= x -1.0)(<= x 1.0)) (-(* pi 0.5) (asin x)))))
(defun asin (x) (cond ((and(> x -1.0)(< x 1.0)) (atan (/ x (sqrt (- 1.0 (* x x)))))) ((= x -1.0) (* -1.0 (/ pi 2))) ((= x 1) (/ pi 2)) ) )
(mapcar 'set '(xa ya za) v1)
(mapcar 'set '(xb yb zb) v2)
(setq ang
(acos
(/
(+ (* xa xb)(* ya yb)(* za zb))
(* (sqrt (+(* xa xa)(* ya ya)(* za za)))(sqrt (+(* xb xb)(* yb yb)(* zb zb))))
)
)
)
(if (< zb za) (setq ang (- (* pi 2.0) ang))) ; to test angle relative to horizontal vector in plane givs angle in full circle
ang
)Command: (rad_to_deg(angles_two_vect v1 v2))
70.5288Miljenko Hatlak
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@Browning_Zed wrote:
....
3rd item - the angle between the first and second obtained points.....
First question: which angle? As already pointed out, the (angle) function operates only in 2D. From Help about it:
The angle is measured from the X axis of the current construction plane, in radians, with angles increasing in the counterclockwise direction. If 3D points are supplied, they are projected onto the current construction plane.
Between two points at different Z coordinates there are two angles -- the one in the XY plane and the one from the XY plane. Draw a LINE with ends at different Z coordinates, and LIST it, or use DIST from end to end, to see both angles. Which of those do you want, or do you mean something else?
@Browning_Zed Function angles_two_vect returns angle in vectors. Conversion to degrees is for easier checkup. @Kent1Cooper has given you good explanation. Extract point from 3dpolyline and create angles between segments. If you want something else, post a sample drawing.
For two points you have vector between them you have three angle components, and you have to separate which one you want. You can check this post in regards vector calculus
Miljenko Hatlak
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@CADaSchtroumpf wrote:
Hi,
Try to change this?
(vlax-curve-getparamatpoint e (setq p (vlax-curve-getclosestpointto e (cadr s))))by
(vlax-curve-getparamatpoint e (setq p (vlax-curve-getclosestpointto e (osnap (cadr s) "_near"))))....
I think that has to be the key, somehow, because if done in the WCS, the Z coordinate of (cadr s) will be 0.0 whatever the Z coordinate of the 3DPolyline at the selection. So the closest point to there on the 3DPolyline will often be somewhere else in XY terms, how far away depending on the configuration of it.
But I would think including both (getclosestpointto) and "nearest" Osnap is redundant -- this much should do the same:
(vlax-curve-getparamatpoint e (setq p (osnap (cadr s) "_near")))
Or maybe the (vlax-curve-getClosestPointToProjection) function would be in order?
(vlax-curve-getClosestPointToProjection e (cadr s) '(0 0 1))
@Browning_Zed wrote:
I need an angle in 2D projection. The angle value is the same can get using your function from this post.
Would
(list pt1 pt2 (angle b a))
work? [Or maybe (angle a b) -- I haven't dug too deep into what's happening.]
