Hi Loïc,
As a cartographer and QGIS user I'd love to see spline or nurbs support
in QGIS. But from a developer point of view (and data format point of
view) it probably opens a can of worms. I do hope that we can get there
eventually.
As you have discovered, besides GML3 and DXF/DWG and ESRI FGDB no other
format seems to support spline/nurbs.
We would have to enhance Postgis as well to handle them - and the
geometry libraries (or we segment them as we do with circular arcs) as
an intermediate step.
I am sure that other devs (e.g. Marco Hugentobler, Nyall, Martin and
others) would have more thoughts on that topic. And maybe Even could
comment from a OGR point of view - what would have to be done to support
splines/nurbs.
Good to see discussion starting on that topic!
Andreas
On 2017-10-16 23:54, L.Bartoletti wrote:
> Hi,
>
> I'm working on an AutoCAD to QGis migration topic for town planners and
> landscapers that made me think about something that I would like your opinion.
>
> I recently committed new features to draw and I have just proposed QEPs to
> improve the drawing "a la" CAD in QGis, but I'm wondering about the
> representation of some geometries and how to manage them well.
>
> There is no known method to transform an ellipse into an arc, so geometry is
> always segmented. Similarly, a circle is represented by several arcs which,
> when a node is modified, can deform the circle.
> I've often seen landscapers or town planners (like me) drawings with splines.
> We don't yet have the possibility to draw it (TODO ;) ) but clearly, how to
> manage it in QGis afterwards?
>
> Even if it's boring to take up again, a circle or ellipse is simple to redraw
> if you want to modify them, but a spline is more complex.
>
> Apart from DXF/DWG formats, I am not aware of the direct support of these
> geometries in GIS formats (maybe GML 3 and those compliant with ISO
> 19107:2003? I didn't know this standard until today), in any case, they don't
> exist in the standard OGC "simple feature access" which seems to be our
> basis, right? Thus, we must convert them: arcs or segments for circles,
> segments for splines and ellipses.
>
> So, how can we keep track of the originals geometries without having to
> convert them?
> Here are some thoughts mixed up ...
>
> - Never mind, we stay with primitive types
> - Added support for existing geometries (circles, ellipses) when formats
> offer it. There is maybe a link to do with GDAL/OGR.
> - We try to be full ISO and we develop all the geometries in QGis :D
>
> For formats that do not support these types, we record at best (arc,
> segments) but for editing:
> - The action is stored in memory and until the editing session is finished,
> the geometry can be modified by moving the quadrants (circles, ellipses) or
> control points (splines)
> - Information is stored in an auxiliary or base file for RDBMS. Thus, when it
> is opened in QGis you can find the information and modify the geometries
> correctly, otherwise it remains open as it is today in arc or segmented. It's
> like an external/"proprietary" feature.
>
> How do you feel about that?
>
> Regards.
>
> Loïc
>
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