arc length

is there anything available that i can choose an arc length?
i need to be able to select 2 points, then select an arc length and the arc be placed between the 2 points at my specified length......

 

This was discussed a few months ago (you should be able to find it on the
web newsgroup site). As I recall, there were some ways to get close, but no
way to do it with precision.

Kent Cooper, AIA

arc be placed between the 2 points at my specified length......

 

Kent is correct,
Here is a program that I experimented with.
As the angle nears 0 the accuracy suffers.
Maybe it will work for what you want.

;03/09/04 Bill Zondlo
;program to get chord and arc length
;then figure included angle, radius and center point.
;
(defun c:arc_2p (/ ctr d h k pt1 pt2 rad s theta x)
(initget 1)
(setq pt1 (getpoint "\nFirst point:") ;first arc point.
)
(initget 1)
(setq pt2 (getpoint pt1 "\nSecond point:") ;end of arc point (chord).
)
(prompt (strcat "\n Length of Chord: < " (rtos (distance pt1 pt2) 2 4) " > ")) ;screen prompt
(initget 7)
(setq s (getdist "\nEnter Length of Arc: < inches >") ;
)
(setq chord (distance pt1 pt2)
k (/ chord s)
y (- 1.0 k)
x (- 24.0 (* 24.0 k))
)
(cond ((> s chord)
;---;
(repeat 8
(if (not (equal x 0.0 1e-5))
(setq x (- x (/ (- (sin x)(* k x))(- (cos x) k))) ;Newton's Method - if arc lengths are not close to chord length.
)
)
) ;end repeat.
;---;
(if (or (minusp x) ;if arc length is close to chord length.
(equal x 0.0 1e-5))
(setq x (sqrt (* (* 6.0 y)(+ 1 ;accuracy suffers on arc lengths that are very
(/ (* 3.0 y) 20.0) ;much longer than the chord or that are very
(/ (* 321.0 (* y 2.0)) 5600.0) ;close to chord length.
(/ (* 3197.0 (* y 3.0)) 112000.0)
(/ (* 445617.0 (* y 4.0)) 27596800.0)
(/ (* 1766784699.0 (* y 5.0)) 179379200000.0)
)
)
)
) ;end setq
) ;end minusp if
;---;
(setq theta (* x 2.0)
rad (/ s theta)
d (* rad (cos x)) ;center to chord distance.
h (- rad d) ;bulge distance (if needed).
ctr (polar pt1 (+ (angle pt1 pt2)(atan d (* (distance pt1 pt2) 0.5))) rad)
)
(entmake (list (cons 0 "ARC")(cons 8 "0")(cons 10 ctr)(cons 40 rad)(cons 50 (angle ctr pt1))(cons 51 (angle ctr pt2))))
)
((<= s chord)
(prompt "\nArc length is shorter or equal to chord.")
)
) ;end cond.
(princ)
)

HTH

Bill