[GRASS-dev] integrate v.concave.hull into v.hull [was point cloud analysis: new features]]

[Blumentrath, Stefan]

Hei Markus,

Not sure I fully understood you problem...

I guess you don`t have a "grouping variable" (e.g. a lake ID) for the contour lines? If you had one, you could probably extract the outer lines based on the attribute table (get max depth by lake (or min depth, depending on how it is coded), something like where="depth=max_depth") and turn them into polygon (if lines are properly closed).

Otherwise, if contour lines are not grouped by lake, personally I might have probably used PostGIS like this:
1) Polygonize all contour lines (ST_MakePolygon), eventually after checking if line strings are properly closed (ST_IsClosed)
2) SELECT all intersecting combinations of polygons in the resulting table (ST_Intersects)
3) LEFT JOIN polygonised contour lines with themselves using ST_CoveredBy
4) SELECT only those where left join IS NULL

Is that somehow in the direction you were thinking?

Cheers
Stefan

> ________________________________________
> Von: grass-dev-bounces at lists.osgeo.org <grass-dev-bounces at lists.osgeo.org> im Auftrag von Markus Neteler <neteler at osgeo.org>

> I have a similar problem: imagine a set of contour lines which
> describe the bathymetry of a lake, so essentially contour lines which
> are closing a polygon but consist of different lines.

> I would like to get the respective polygon representation, i.e. the
> outer lines only and those turned into a polygon.

> I just tried v.concave.hull on it, however, it expects points and not lines.
> Does anyone have an idea how to achieve that?

> thanks
> markusN