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  3. Is there a way to get outer points of selected polygons...

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Is there a way to get outer points of selected polygons?

kbhow
kbhow over 14 years ago

Hi,

Is there any SKILL codes which able to get the outer points of selected objects?

I was trying to create a new function which may required to get the outer points of selected objects (polygon/rectangle/instances and etc). I want to get a list of points where i can use it to create a polygon which cover all selected objects.

Example, let say i have selected 10 polygons, and i want a function to return me a list of outer points of my selected object. Can someone help?

Thanks

How

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  • StefanSL
    StefanSL over 14 years ago
    Hi kbhow,

    regarding the boolean operation, i assume dbLayerOR should be more useful than ANDcause you want to combine all your selected objects; of course, just ORing the shapes will result in a shape covering all your shapes but you might get more than one shape and your shape might have holes in it.

    If i understand your needs correctly, the keyword "convex hull" might be what you are looking for:  the minimum convex polygon including all your shapes.

    Starting point would be a list of all points of all your selected shapes; searching for "convex hull", "computational geometry" should lead to an algorithm to get the convex hull from this set of points; possibly you should export the problem to a perl-script for better performance and access to trigonometric functions.

    If the convex hull is too large, the problem will become much more complicated cause you'd have to define how concave, how "deep" concave the polygon may be.

    Kind regards

    Stefan
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  • StefanSL
    StefanSL over 14 years ago
    Hi kbhow,

    regarding the boolean operation, i assume dbLayerOR should be more useful than ANDcause you want to combine all your selected objects; of course, just ORing the shapes will result in a shape covering all your shapes but you might get more than one shape and your shape might have holes in it.

    If i understand your needs correctly, the keyword "convex hull" might be what you are looking for:  the minimum convex polygon including all your shapes.

    Starting point would be a list of all points of all your selected shapes; searching for "convex hull", "computational geometry" should lead to an algorithm to get the convex hull from this set of points; possibly you should export the problem to a perl-script for better performance and access to trigonometric functions.

    If the convex hull is too large, the problem will become much more complicated cause you'd have to define how concave, how "deep" concave the polygon may be.

    Kind regards

    Stefan
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