HOW TO: self referencing vla-i

SOliver · 发表于 2022-7-6 09:39:31

Alright folks,

I've made this post for two reason: Firstly I spent a fair bit of time looking through google on this subject with practically no pointers on how to achieve the above - so I thought "I'm sure the forum will find this interesting". Secondly: If this is wrong I'm sure someone will spot the error before I do. If this is old news then let the thread die - hate the code not the coder lol

So I've been scraping the internet looking for a efficient (not create-a-region) based approach to determining if a lwPolyline intersects with it's self. Anyway after a bit of lethargy-fuelled critical thinking I discovered the following.

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(defun c:sample( / ) (setq ply(vlax-ename->vla-object(car (entsel "\nSelect polyline")))) (setq uBound(vlax-safeArray-get-u-bound(vlax-variant-value(vla-get-coordinates ply)) 1)) (setq intUBound(vlax-safeArray-get-u-bound(vlax-variant-value(vla-intersectWith ply ply acExtendNone)) 1)) (princ "\nCoord len: ")(princ uBound) (princ "\nInter UB: ")(princ intUBound) (if(> intUBound uBound)   (princ "\nIntersects with self")    (princ "\nDoes not intersect with self") ) (princ))

From what I can tell every point along a polyline is considered to be an  intersection when self referencing an object with the vla-intersectWith  method.

Since each point is considered an intersect a non self-intersecting  lwPolyline will have the same safeArray upper bound as that of the  results from vla-intersectWith -  if they differ then the lwPolyline  intersects itself.

EDIT:

In hindsight I probably shouldn't have called this a "how to"  given that the information may be redundant || not validated by a group of peers.

Enjoy, use or disprove at your own leisure.

Lee Mac · 发表于 2022-7-6 10:18:17

Nice one SOliver

You might want to considering approaching it this way to avoid the Variants - but they both ultimately use the same method:

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(defun SelfIntersecting ( poly ) (< (length (vlax-get poly 'Coordinates)) (length (vlax-invoke poly 'IntersectWith poly 0))))

Lee

SOliver · 发表于 2022-7-6 10:29:39

Thanks Lee.

I never realised until I read your code that vlax-get and vlax-invoke provide a standard list in the return. Would it be fair to say that that when using vlax-* methods (pertaining to safeArrays) the return will be in standard list format as opposed to vla-* methods which true to nature will return a safeArray of sorts?

Lee Mac · 发表于 2022-7-6 10:44:21

The vlax-get/invoke are undocumented and will return the data in native AutoLISP formats - however, IIRC there are a few methods/properties for which they fail.

[编程交流] HOW TO: self referencing vla-i

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