Behavior of arc "reversed", DXF compatibility?

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Behavior of arc "reversed", DXF compatibility?

Postby swissguest » Sat Nov 02, 2013 12:44 pm

There is a "reversed" flag on arcs. I can set this to true, and swap start and end angle - in order to change the direction of an arc. The screen rendering in QCAD gets updated when I do this. However, the DXF file written before and after these changes is just the same, so I cannot tell if / how the arc "reversed" property has any effect. Obviously, reloading this DXF file would then show the arc with the original, unchanged values.

Fyi, it is very helpful to have the ability to change the direction of DXF entities - when the DXF is imported into a CAM software - and this software calculates CNC machining paths based on the order of points (for lines and splines). I hope to achieve the same for arcs.

However, I am not even sure if this is possible, and / or supported by the DXF format for arcs specifically. Hence, I do not know if this is a defect or expected behavior, and why the "reversed" property is offered by QCAD.

Version: 3.4.2.0 (3.4.2)
Build Date: Oct 25 2013
OS: Ubuntu Linux 12.04 64 bit
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Re: Behavior of arc "reversed", DXF compatibility?

Postby andrew » Sat Nov 02, 2013 12:50 pm

swissguest wrote:However, I am not even sure if this is possible, and / or supported by the DXF format for arcs specifically.


Unfortunately, DXF does not support that which is why arcs are always stored clockwise.

QCAD offers this choice for other output formats for example the G-Code output of the CAM add-on.
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Re: Behavior of arc "reversed", DXF compatibility?

Postby andrew » Sat Nov 02, 2013 12:51 pm

PS: As a workaround, you can convert an arc to a polyline with a single arc segment (Draw - Polyline - From Segments). That is if polylines are supported by your machine.
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Re: Behavior of arc "reversed", DXF compatibility?

Postby swissguest » Sat Nov 02, 2013 12:59 pm

Thanks for the clarification!
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