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

[DelazJ]

Hi Martin

2018-06-21 13:08 GMT+02:00 Martin Dobias <wonder.sk at gmail.com>:

> Hi Harrissou
>
> On Thu, Jun 21, 2018 at 12:55 PM, DelazJ <delazj at gmail.com> wrote:
> > Hi,
> >
> > I've raised the question [0] but I did get no answer two weeks later so
> > making a wider call
>
> Sorry it seems my mail filters failed and I missed your notification...
>
> no problem.

>
> > Select a polyline layer and toggle it to edit
> > Draw a polyline
> > Configure the snapping options
> > Enable the tracing tool and add a positive value in the offset option box
> > Draw a new line following the one previously made
> >
> > According to all the sources I find (PR, .h file): """ Offset value can
> be
> > either positive (right side) or negative (left side)."""
> >
> > Is the line being drawn at the right or the left? Right or left of what,
> > btw?
>
> 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 to bother with what may look like details but...

Thanks,
Harrissou

Cheers
> Martin
>
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