[gdal-dev] Reading error with dwg and dxf files

[Even Rouault]

Selon Xian Chen/³ÂÏÛ <chenxian at walkinfo.com.cn>:

> Thanks Even.
>
> After checking the code under dwg and dxf, I believe the relevant error code
> to my original error report should be in
> ogr/ogrsf_frmts/dxf/ogrdxf_polyline_smooth.cpp. The code in EmitArc() must
> consider the case when ogrArcStartAngle > ogrArcEndAngle and bClockWise is
> true before calling OGRGeometryFactory::approximateArcAngles() (around line
> 265). Here I increase the value of ogrArcEndAngle by 360 degree as follows:
>     if( bClockwise && (ogrArcStartAngle > ogrArcEndAngle) )
>         ogrArcEndAngle += 360.0;
>
> Then the reported error is corrected.
>
> Similarly, there are error codes in both ogrdxf_hatch.cpp and
> ogrdwg_hatch.cpp as you mentioned.
> Line 286-294 in ogrdxf_hatch.cpp are quite suspicious:
>             if( bCounterClockwise )
>             {
>                 double dfTemp = dfStartAngle;
>                 dfStartAngle = dfEndAngle;
>                 dfEndAngle = dfTemp;
>             }
>             if( dfStartAngle > dfEndAngle )
>                 dfEndAngle += 360.0;
>
> Can anyone explain to me why switching Start Angle and End Angle (this will
> reverse the order of the line string!!). Also, if bCounterClockwise, you
> won't want to increase dfEndAngle by 360..
>
> I've fixed the above code with something like:
>             if( bCounterClockwise )
>             {
>                dfStartAngle *= -1;
>                dfEndAngle *= -1;
>             }
>             else if( dfStartAngle > dfEndAngle )
>                 dfEndAngle += 360.0;
>
> Similar fix-up is made in ogrdwg_hatch.cpp
>
> Not sure if these are sufficient, yet at least work well with my couple of
> sample dwg/dxf files.
>
> I may want to submit a patch if you and other developers are okay with my
> fix-up.

Xian,

I'm not familiar with that code, so I am not sure about your proposed fix, but
it could be helpful if you attach it to a ticket so it doesn't get lost.
Attaching sample .dxf and .dwg files that have the issue that the patch fixes
would also be helpfull.

Best regards,

Even