Code Red > AutoLISP (Vanilla / Visual)

Arc-length from known radius & chord

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DMSS1:
I have a radius of 1326.0
And a chord of 72.0

How can I find the arch length using autolisp?

Thanks,
DMSS1

LE:
Welcome;

I think there are a lot of geometry formulas out there, here is what I had used"


--- Code: ---(setq arcAngle
       (* (atan (/ (/ (sqrt (- (expt radius 2) (expt (/ chord 2.0) 2))) 2.0) chord))
  2.0))

(setq arcLength (* (* (/ (/ (* arcAngle 180.0) pi) 360.0) (* pi 2)) radius))

--- End code ---

I did a quick translation to my formulas I have in C++, into autolisp, hope they are right (not tested)

Update: Removal of the C++ code - not needed here.

DMSS1:
Thanks Esquivel!
I will try-it-out.

The only part I don't understand is "pow" (is this POINT-ON-WORLD coords?).

LE:

--- Quote from: DMSS1 on July 31, 2006, 01:34:54 PM ---The only part I don't understand is "pow" (is this POINT-ON-WORLD coords?).

--- End quote ---

No no.... the commented code is in C++.... I just posted as reference.

DMSS1:
I tried it out, but got the wrong answer.

Radius=1326.0 of a circle.
Chord=72.0

Find the length of arc with a 72.0 chord on the circle.

My dwg says the angle bettween the intersections=3.11146537°
And the arc length=72.00884796

I drew a circle, r=1326.0
Then drew a line 72.0
Moved the middle of the line, to the top quadrant of the circle.
Then drew a line verticaly to the inside of circle on each side.
Drew a line from inersection to intersection (this should produce a 72.0 straight line across the to of the circle).
Trim the big circle with the new horizontal line.
Listing the arc = length above.

Did I do smething wrong?

Thanks,
DMSS1

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