Determining if two areas are overlapping

[bdwidhalm]

Does anyone know how to (using AutoLisp or Visual Lisp) determine if two areas are overlapping? The areas will be defined by polylines which could make up any shape. I need to figure out how to check if they are overlapping even the slightest bit, I've been racking my brain on how to start this but I'm drawing a blank. I would greatly appreciate any ideas on how to determine this, no one needs to write the code for me, just throw me some ideas/psuedo-code to get me rolling. I've been looking in the help files for any commands that might be useful but haven't found any. I'm not sure how I can compare the vertices of the areas to determine if they overlap, I thought of maybe converting them to solids and somehow using Interference Checking or the Intersect command (the polylines would all be drawn at zero elevation or flattened). I haven't gotten any code put together for that even yet so any ideas on how to do this in a very simple manner would be greatly appreciated.

I attached a simple drawing showing two areas overlapping.


Thanks!

[T.Willey]

The method ' IntersectWith ' will let you know if two objects intersect with each other.

[bdwidhalm]

Isn't that VBA? I haven't done alot of VBA, would like to get this done with LISP.

The method ' IntersectWith ' will let you know if two objects intersect with each other.

[T.Willey]

You can use it with lisp. It is ActiveX. Just load the arx file that will allow you to; ' (vl-load-com) '. This will return T if they intersect, and nil if not, to the command line.

(defun c:IntersectTest (/ Sel Ent Obj1 Obj2)
    
    (vl-load-com) ; only needs to be called once per session, but doesn't matter if called more times.
    (and
        (setq Sel (entsel))
        (setq Obj1 (vlax-ename->vla-object (car Sel)))
        (setq Sel (entsel))
        (setq Obj2 (vlax-ename->vla-object (car Sel)))
        (vlax-invoke Obj1 'IntersectWith Obj2 acExtendNone)
    )
)

[bdwidhalm]

I see... Thank you, I wasn't sure how to call VBA from LISP. That would be very helpful!

Thanks.

You can use it with lisp. It is ActiveX. Just load the arx file that will allow you to; ' (vl-load-com) '. This will return T if they intersect, and nil if not, to the command line.

(defun c:IntersectTest (/ Sel Ent Obj1 Obj2)
    
    (vl-load-com) ; only needs to be called once per session, but doesn't matter if called more times.
    (and
        (setq Sel (entsel))
        (setq Obj1 (vlax-ename->vla-object (car Sel)))
        (setq Sel (entsel))
        (setq Obj2 (vlax-ename->vla-object (car Sel)))
        (vlax-invoke Obj1 'IntersectWith Obj2 acExtendNone)
    )
)

[T.Willey]

It can be very powerful, but also sometimes it will take longer. Only with experience and testing will one know for sure, but it is a good tool to have in your tool bag.

You're welcome.

[irneb]

I see... Thank you, I wasn't sure how to call VBA from LISP. That would be very helpful!

Thanks.

It's not actually VBA you're calling. It's named ActiveX ... which is an Extension Library which can be called from any (well ... most) programming languages. VBA is simply the norm in most applications.

The Visual Lisp extensions allowed this to be called in Lisp. And yes, some things are much easier to do with these methods, while some things are possible only through these methods, and yet other things are only possible through normal AutoLISP. So it depends on the situation, but generally it's easier quicker & more efficient to use the vlax / vla methods.

Also a shorthand way of executing the Method is to replace the line:

(vlax-invoke Obj1 'IntersectWith Obj2 acExtendNone)

with

(vla-IntersectWith Obj1 Obj2 acExtendNone)

[T.Willey]

Also a shorthand way of executing the Method is to replace the line:

(vlax-invoke Obj1 'IntersectWith Obj2 acExtendNone)

with

(vla-IntersectWith Obj1 Obj2 acExtendNone)

True, but if you used to working in lisp, one will give you a list of points, and the other will be a variant. I like working with lists instead of variants, so that is why I posted it the way I did.