Problems importing QCAD DXF files into SignLab

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Problems importing QCAD DXF files into SignLab

Postby md_walker » Mon Sep 29, 2008 5:55 am

I have run into a couple of problems with importing QCAD DXF files into my CNC supplier's application. I am using QCAD v2.2.2.0, running on Windows XP SP2. The application they use is SignLab.


The first, and biggest issue is that the same arc in 2 different drawings has been interpretted very differently ... once as the arc as drawn, and once it appears as a spline kind of object. The end result has been items that should have a matching arc have been cut differently, and noticably so.

The arc was created in one drawing, then copied into the other, as well as being copied, flipped and rotated for different matching pieces in both drawings ... all the instances of it in one drawing worked, and all in the other didn't.

The arc is one of three linked end-to-end to make a single curve. In both of the drawings the arc is part of a polyline which groups together the complete outline of the component.


We also had a consistent issue across all of the drawings I supplied, where they were created with 'mm' as the units, but always imported as inches ... dimension values didn't change or scale, it just saw them as inches.


Also when talking to them about the issue with the arc they re-imported my drawings to lay one version over the other and see how they miss-aligned. It seemed to oddly scale one of the drawings as other items on the drawings that should line up no longer did.


I have checked the drawings in QCAD, and they are correct with everything lining up. I have even checked the properties of all the instances of the arc in question and they are correct.


Has anyone else run into this sort of problem?
Any hints / tips on making sure imports work consistently between drawings?


Mark.
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Re: Problems importing QCAD DXF files into SignLab

Postby andrew » Wed Oct 01, 2008 8:56 pm

md_walker wrote:The first, and biggest issue is that the same arc in 2 different drawings has been interpretted very differently ... once as the arc as drawn, and once it appears as a spline kind of object. The end result has been items that should have a matching arc have been cut differently, and noticably so.


This sounds like an import problem of the other product. QCAD stores arcs as arcs in the DXF file. Maybe there is an import option of the other product to avoid this conversion?

md_walker wrote:The arc was created in one drawing, then copied into the other, as well as being copied, flipped and rotated for different matching pieces in both drawings ... all the instances of it in one drawing worked, and all in the other didn't.


Maybe the other product cannot handle arcs that are either clockwise or counter-clockwise. Just a wild guess though.

md_walker wrote:The arc is one of three linked end-to-end to make a single curve. In both of the drawings the arc is part of a polyline which groups together the complete outline of the component.


You could try to break up the polyline and let the other product import three single arcs instead.

md_walker wrote:We also had a consistent issue across all of the drawings I supplied, where they were created with 'mm' as the units, but always imported as inches ... dimension values didn't change or scale, it just saw them as inches.


QCAD stores the unit of the drawing in the DXF file. It looks like the other product is ignoring this information and simply imports everything in Inches. Again, there might be a setting in the other product to avoid this.

md_walker wrote:Any hints / tips on making sure imports work consistently between drawings?


Some other things you can try:
- Export your drawing for them as DXF R12 (see "save as" dialog).
- Break up complex entities (such as polylines, blocks, etc.). Generally, simple entities such as lines, arcs or circles usually do not cause problems.
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Postby md_walker » Mon Oct 06, 2008 9:07 am

Thanks for the help.

Turns out it is a problem with SignLab's interpretation of the arc.

In the instance where it worked the arc was between a short straight line and another similar largte radius arc ... in this case it had no problem as it properly recognised the end of one object and start of another.

In the one that failed one end of the arc was connected to a very small radius arc which went in the oposite direction ... in this case it seemed to try 'smoothing' the path from this 'round over' arc to the next arc, hence the slight resulting 's' shape like it was a spline.

We tried importing a version without the full outline connected as a 'polyline' and it handled that OK ... but to do the cutting it needed to be as a polyline in the end.

End result is that next time I get something CNC cut I will provide both a polyline and non-polyline version and get them to lay one on the other to make sure the program has correctly interpreted the drawing. For the current 'problem' drawing the solution is a very short straight line between the large arc and the round-over arc.

Thanks again for the help.
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