Closed Polyline or not ....

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Closed Polyline or not ....

Postby Husky » Tue Oct 15, 2013 7:27 pm

Hi - just a question to my understanding ..... :oops:

What is the exact difference between a closed or not closed Polyline?

If I draw a Polyline (i.e. Rectangle shape) and finish this rectangle with an exact end snap point to the start of the Polyline - the property editor tells me this Polyline isn't closed.
If I use the Option Bottom "close Polyline" the property editor tells me it is closed.
If I draw an offset line based on this closed Polyline - the offset will be not closed ....

What is the secret of this closed yes/no information ...... 8)
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Husky
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Re: Closed Polyline or not ....

Postby andrew » Tue Oct 15, 2013 7:53 pm

This originates from the DXF / DWG file formats. These formats define an open/closed flag for polylines.
A rectangle formed from a closed polyline only needs four vertices, whereas an open polyline would require five vertices to form a closed rectangle.

For most purposes, the end result is the same (a closed rectangle).

The only case I can remember in which it does make a difference is if the file produced by QCAD will be processed further by other software. There are certain types of machine controllers for example in electron-beam-lithography that treat properly closed polylines differently.
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Re: Closed Polyline or not ....

Postby Husky » Tue Oct 15, 2013 8:20 pm

Now I have an good Idea what the difference is - thanks for explaining it to me. :D
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