Longest leg of a Rectangle

Hello,

Would anyone know how I would determine the long leg of a rectangle if I
already have the points for the rectangle contained in a list. Could this be
done using plain AutoLisp?

Thanks,
Mark

 

I would extract the X coordinates and the Y coordinates from the points.
Subtract one from the other then compare the 2. The larger one is the longer
one.

There is probably an easier way... I always seem to do things the hard way.

Rick

 

I would extract the X coordinates and the Y coordinates from the points.
You should only need 2 diagonal points.
Subtract one from the other then compare the 2. The larger one is the longer
one.

There is probably an easier way... I always seem to do things the hard way.

Rick

 

Check the distances:

Command: (setq dslst (list (distance pt1 pt2)(distance pt2 pt3)(distance pt3
pt4)(distance pt4 pt1)))
(17.5202 10.088 17.846 10.6433)

Command: (setq longest (apply 'max dslst))
17.846

Command: (setq index (- (length dslst)(length (member longest dslst))))
2

This would give you the 3rd element of the point list.

HTH

Bill

 

This could work if you assume that pt1 and pt2 aren't by accident the diagonal points of the rectangle!
I think first you have to find out what lines are parallel to each other and then get the greatest distance?

Jim

 

Thanks all for your help. Actually Jimmy is correct I don't always know in
what order the point list will be.

Mark

diagonal points of the rectangle!

and then get the greatest distance?

 

I guess it goes to the old saying:

Assume broken down makes an Ass-u-me.....

Bill

 

If you take the distances from one point to each of the other three points -
assuming it's a rectangle and not a parallelogram - then the greatest length
will be the diagonal and the other two will be the short and long side
dimensions, regardless of the order of the point list.

(setq dslst (list (distance pt1 pt2)(distance pt1 pt3)(distance pt1 pt4)))
(setq dslst (vl-sort dslst '<)) ;ascending order
(nth 0 dslst) ;short dimension
(nth 2 dslst) ;long dimension

 

Thanks Tom that works!

 

Thanks Tom that works!

No prob. Remember, it won't work if it's not a true rectangle. That would
require another test.