[QGIS-Developer] Looking for my right and my left

[DelazJ]

Thanks for having checked,

Harrissou

2018-06-21 15:25 GMT+02:00 Martin Dobias <wonder.sk at gmail.com>:

> Hi again
>
> On Thu, Jun 21, 2018 at 1:38 PM, DelazJ <delazj at gmail.com> wrote:
> >>
> >> It should be left/right when looking from the direction of the
> >> original line. So for example if the original line goes from bottom to
> >> the top, the left/right side should be the same as the map
> >> orientation, but if the line goes from the top to the bottom, then the
> >> left/right side would be reversed...
> >>
> > Sorry but still I do not get the relation with the behavior whether I
> set a
> > positive or negative value.
> >
> > I draw a line from bottom to top
> > then I snap to the lower point and trace with a positive offset: the new
> > line is placed on the left side of the screen (should it? Positive value
> > goes right), and coincidentally the left of the tracing direction.
> > If I snap to the higher point and trace with the positive value: the new
> > line is placed on the right side of the screen, and coincidentally still
> the
> > left of the tracing direction.
> >
> > It looks like it has not to do with the _direction of the original line_
> but
> > with the direction of the trace. And that positive value rather goes to
> left
> > (unlike doc statement)
>
> Sorry for the confusion - I have checked again and you are right:
> - direction is determined from the traced line (not the original line
> orientation)
> - positive offset = left side, negative offset = right side (as
> documented in [1] - see GEOSOffsetCurve_r)
>
> [1] https://geos.osgeo.org/doxygen/geos__c_8h_source.html
>
> Cheers
> Martin
>
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