Need Start/End angles (orientation in space) from 3 coordinates

Darren, did you see my final version yesterday? Luis replied shortly after I

Yes I did. Thanx!

--
Darren J. Young
CAD/CAM Systems Developer

Cold Spring Granite Company
202 South Third Avenue
Cold Spring, Minnesota 56320

Email:
Phone: (320) 685-5045
Fax: (320) 685-5052

 

I know zip about splines.
When it comes to plines the bulge factor will tell you what direction the arc travels.
If you already have 3 points that define the arc, you use the sagitta method that I used in both of my programs.

rad = (/ (+ (expt d 2)(expt h 2))(* h 2.0))
cen = (polar p2 (+/- (angle p1 p3)(* pi 0.5)) rad)

HTH

Bill

 

I know zip about splines.

True, however I'm not actually pulling and polyline "segment" specific
geometry. I'm using the vlax-curve functions to extract points along the
polyline (or spline) at pre configured distances. The area where I could
be laying a new arc down just might span partially across a straight
segment and a curved segment. In the case of one file in particular it's
going to be used on, there are no arcs in the polyline, it's all zigzag
line segments (I'm assuming it was scanned and vectorized). My program
will come back through and redraw with a singe arc what's not several
hundred zigzag line segments that "happen" to make an arc shape.

Ok, looking back at your first program, I see where you are going.
That's would have worked, (although I'm to far into the code now to
switch to your method) I'd have only needed to make one modification and
that would have been to flag if the start/end points needed swapping or
not and return it along with the start/end angles in a list to the
calling function.

If I have time, perhaps I'll integrate it. Although I still would Jeff's
code because it was more componentized which allows me to use it as
library functions to pull other types of data and mix and match it with
some of my own functions.


--
Darren J. Young
CAD/CAM Systems Developer

Cold Spring Granite Company
202 South Third Avenue
Cold Spring, Minnesota 56320

Email:
Phone: (320) 685-5045
Fax: (320) 685-5052

 

Good Luck!

Bill

 

Jeff (and others)

You need a slight modification to your RAD3PTS function to check if the
points are colinear (180deg arc) in which case, your function would
produce a divide by zero error.

(defun rad3pts (p1 p2 p3 / A B C R q)
(setq A (distance p1 p2)
B (distance p2 p3)
C (distance p1 p3)
)
(if (= (+ A B) C)
A
(progn
(setq q (/ (- (+ (expt A 2) (expt B 2)) (expt C 2)) (* 2 A B)))
(/ C (* 2 (sqrt (- 1 (expt q 2)))))
)
)
)

--
Darren J. Young
CAD/CAM Systems Developer

Cold Spring Granite Company
202 South Third Avenue
Cold Spring, Minnesota 56320

Email:
Phone: (320) 685-5045
Fax: (320) 685-5052

 

Correction to me correction. Note to self...returning the center point
not the radius. ;^)


(defun rad3pts (p1 p2 p3 / A B C R q)
(setq A (distance p1 p2)
B (distance p2 p3)
C (distance p1 p3)
)
(if (= (+ A B) C)
p2
(progn
(setq q (/ (- (+ (expt A 2) (expt B 2)) (expt C 2)) (* 2 A B)))
(/ C (* 2 (sqrt (- 1 (expt q 2)))))
)
)
)


--
Darren J. Young
CAD/CAM Systems Developer

Cold Spring Granite Company
202 South Third Avenue
Cold Spring, Minnesota 56320

Email:
Phone: (320) 685-5045
Fax: (320) 685-5052

 

Corrected correction to my correction. Just can't think straight. If
it's wrong the heck with it. You get the idea.

(defun rad3pts (p1 p2 p3 / A B C R q)
(setq A (distance p1 p2)
B (distance p2 p3)
C (distance p1 p3)
)
(if (= (+ A B) C)
(mapcar '/ (mapcar '+ p1 p3) '(2 2 2))
(progn
(setq q (/ (- (+ (expt A 2) (expt B 2)) (expt C 2)) (* 2 A B)))
(/ C (* 2 (sqrt (- 1 (expt q 2)))))
)
)
)


--
Darren J. Young
CAD/CAM Systems Developer

Cold Spring Granite Company
202 South Third Avenue
Cold Spring, Minnesota 56320

Email:
Phone: (320) 685-5045
Fax: (320) 685-5052

 

AHHHHHHHHHHHHHHH! Undo the corrected correction and the correction, wr'e
back to the original update. Yes we are returning a radius....I was
looking at the function that called this (which returned the center).
VERY long week.

(defun rad3pts (p1 p2 p3 / A B C R q)
(setq A (distance p1 p2)
B (distance p2 p3)
C (distance p1 p3)
)
(if (= (+ A B) C)
p2
(progn
(setq q (/ (- (+ (expt A 2) (expt B 2)) (expt C 2)) (* 2 A B)))
(/ C (* 2 (sqrt (- 1 (expt q 2)))))
)
)
)

--
Darren J. Young
CAD/CAM Systems Developer

Cold Spring Granite Company
202 South Third Avenue
Cold Spring, Minnesota 56320

Email:
Phone: (320) 685-5045
Fax: (320) 685-5052