topic Re: "ResizeContour" does not work as expected in Libraries & objects

"ResizeContour" does not work as expected

runxel — Wed, 17 Mar 2021 16:52:06 GMT

If you use the "ResizeContour" operation of the PolygonOperations-Addon I would expect that the resulting polygon is offsetted in all directions.
But clearly something terrible has happened here:

You see, the "start" point of the closed (!) polygon was not taken into account in the right manner. Now I have this corner chamfered away, gone for good.
The expected behaviour should be of course a new rectangle....

Re: "ResizeContour" does not work as expected

Lingwisyer — Thu, 18 Mar 2021 01:34:05 GMT

Reminds me of when you try to offset a polygon that is not closed in AutoCAD... Is there a way to ensure that the input polygon is closed?

Re: "ResizeContour" does not work as expected

runxel — Wed, 31 Mar 2021 22:33:34 GMT

No solution, GS?

Re: "ResizeContour" does not work as expected

Pertti Paasky — Sat, 03 Apr 2021 19:31:20 GMT

Hi, can You share Your object placed in a .pla file? No other way I can comment this problem. Polygon operations usually work fine. Maybe there is something wrong with the initial data. I have found some bugs in the add-on and example objects.

Re: "ResizeContour" does not work as expected

Peter Baksa — Fri, 09 Apr 2021 14:07:11 GMT

Hi runxel,

the problem is probably that when working with dicts, PolyOperations "ResizeContour" expects a polygon whose last point is not the same as the first.

Dict polygons always have to be closed, polylines can be open or closed. A closed polyline/polygon means the last point is not the same as the first (think of it as auto-closed). An open polyline has one more vertices than edges.

Re: "ResizeContour" does not work as expected

runxel — Fri, 14 May 2021 19:35:12 GMT

Peter wrote:
the problem is probably that when working with dicts, PolyOperations "ResizeContour" expects a polygon whose last point is not the same as the first.

Dict polygons always have to be closed, polylines can be open or closed. A closed polyline/polygon means the last point is not the same as the first (think of it as auto-closed). An open polyline has one more vertices than edges.

Thank you Péter! That is exactly the right hint.
What I did was to insert a final new point which is coincident with the first point. When doing that the result will look like in my picture above.
Would be great if this info of auto-closing polygons could be a bit more prominent in the manual.
It was also quite unclear for me why there is a distinction made between polygons and polylines in the first place.