[GRASS-user] link each region to the unique input point it contains in v.voronoi?

[Markus Metz]

On Tue, Nov 28, 2017 at 3:34 AM, 洪朝貴 <ckhung at cyut.edu.tw> wrote:
>
> Hi All,
>
> There is a one-to-one correspondence between each point
> of the input point set and a region in the output region set
> of the Voronoi diagram. Is there a way (say, adding
> an attribute column?) to create the two way links between
> these two data sets?
>
> An unrelated minor question: the output of v.voronoi can be displayed,
> but it does not pass the geojson validator:
> https://github.com/mapbox/geojsonhint
> The orientation of the output regions seem to be the opposite
> of the geojson specification. I guess the responsibility
> of ensuring the correct orientation falls more on v.voronoi
> than on v.out.ogr (which outputs the geojson file)?

v.voronoi produces boundaries, and areas are constructed from these
boundaries. GRASS uses a topological vector model, see
https://grass.osgeo.org/grass73/manuals/vectorintro.html#vector-model-and-topology

The correct orientation of polygons must not be assured by v.voronoi or
v.out.ogr, but by OGR. According to OGC simple feature specification,
polygons must be oriented counter-clockwise, interior rings are oriented
clockwise. But e.g. according to ESRI shapefile specifications, the
orientation is opposite to the OGC specification: polygons must be oriented
clockwise, inner rings are oriented counter-clockwise.
Therefore I would defer the responsibility to provide the correct
orientation for each output format to OGR.

Markus M

>
> Thanks!
>
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