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Re: LibreCAD for 3D design - problem with hatching

Posted by jluscher on May 02, 2014; 12:58am
URL: https://forum.librecad.org/LibreCAD-for-3D-design-problem-with-hatching-tp5709872p5709881.html

WOW !

The technique of moving the entities, offset, to find / eliminate gaps is a great idea.

It would be a great "user feature" if the code which detects the gap originally

had a way of highlighting it - even if it stopped at the first (if there were several)

- just before it showed the ERROR message about the contour error.

It would have saved me reporting a problem as I examined the countour, by zooming

in a LOT, and slowly crawling along the lines - but I just couldn't see any gaps.

In general it is a great help to point out the specific location of a problem to

naive users (like me ;-) if nothing else as a teaching tool, immediate feedback

is usually a great help in figuring out what I've done wrong.

Thank you AGAIN for your time and patience in looking so carefully into what

was in the end MY mistake ! I'm sorry about distracting you from other

work.

Sincerely,

James

---- www.jluscher.com ----

r > g = :-(

-- Thomas Piketty, "Capital in the Twenty-First Century"

On Thu, May 1, 2014 at 2:45 PM, dxli [via LibreCAD] <[hidden email]> wrote:

some troubleshooting shows it's a contour connection issue instead of a bug of LibreCAD.

Basically, there are many gaps at 0.001 or 0.0001 level in your contour. I took some time to modify your drawing to create a continuous contour, and hatching works after that. Please test the contour on the right side (on layer 2)

It's not trivial for most users to notice this gype of gaps, without enabling the debugging code for hatching. Since your connections are mostly tangential, a very tricky case for "trimming". Trimming tries to modify the entities to be only within one side of the limiting border, but tangential lines doesn't cut entities into halves.

I didn't spend time to check whether these gaps are from polyline creation (if so, it's a bug of polyline). I explode the polylines, and move entities away:

1, move first entity away by some offset;
2, move the subsequent entities by moving it's startpoint to the end point of the previous moved entities, by snap to end points only. This is an efficient way to remove gaps. I have to zoom in to make sure I'm using the right end points.
3, continue until I moved away exact one sixth of the contour;
4, given a partial contour of one sixth of the whole contour, still need to define a rotation center from which the one sixth of contour spans 60 degrees.
To find the rotation center. you may draw construction circles centered at each end point of this partial, with a radius of the distance between those two end points. one of the intersections between the two construction circles is the rotation center.

hatch1.dxf

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