[GRASS-dev] Which v.* modules are working with v.external'ed data

Markus Metz markus.metz.giswork at gmail.com
Thu Nov 16 13:20:52 PST 2017


On Thu, Nov 16, 2017 at 10:02 PM, Markus Neteler <neteler at osgeo.org> wrote:
>
> On Wed, Nov 15, 2017 at 10:03 PM, Markus Metz
> <markus.metz.giswork at gmail.com> wrote
> > On Wed, Nov 15, 2017 at 4:35 PM, Markus Neteler <neteler at osgeo.org>
wrote:
> >>
> >> On Wed, Nov 15, 2017 at 3:49 PM, Markus Metz
> >> <markus.metz.giswork at gmail.com> wrote:
> >> > On Wed, Nov 15, 2017 at 1:36 PM, Helmut Kudrnovsky <hellik at web.de>
> >> > wrote:
> >> >>
> >> >> Background of the question in subject: the GRASS algs in upcoming
QGIS3
> >> >> are working with v.external linked data.
> >> >>
> >> >> I've seen some modules doesn't work with such kind of data.
> >> >>
> >> >> Is there maybe a list already available?
> >> >
> >> > It depends also on the format that is linked in with v.external. For
all
> >> > formats that do not have a key column (e.g. shapefile), attributes
are
> >> > not
> >> > accessible, and attributes would get lost when modifying the
> >> > geometries.Therefore it is generally not safe to link vector data
with
> >> > v.external. In many cases it does not make sense to use v.external
> >> > linked
> >> > data with simple features, instead vector data should be imported to
get
> >> > true topology. If upcoming QGIS3 is working with v.external linked
data,
> >> > the
> >> > GRASS interface of QGIS is effectively broken.
> >>
> >> I have turned this into a potential new snippet for the v.external
manual:
> >>
> >> ----- snip -----
> >> Due to these data model differences <em>v.external</em> does not work
> >> with all data formats. In general, for all formats that do not have a
> >> key column (e.g. SHAPE file), attributes are not accessible, and
> >> attributes
> >> would get lost when modifying the geometries. Therefore it is generally
> >> not safe to link vector data with <em>v.external</em>. In many cases it
> >> does not make sense to use <em>v.external</em> linked data with simple
> >> features, instead vector data should be imported with <em>v.import</em>
> >> or <em>v.in.ogr</em> to get true topology support. Importantly, point
> >> cloud data which do not have topology, can be linked with
> >> <em>v.external</em>
> >
> > as long as there are no attributes attached to these point cloud data,
or if
> > the format of the point cloud data has a key column that allows to link
> > vector geometries to attributes.
>
> Thanks, added in r71743 (and backported).
>
> >> ----- snap -----
> >>
> >> Please review.
> >
> > Importing point cloud data is fast, therefore there is little gain in
using
> > v.external instead of v.in.ogr.
>
> I wonder how much disk space that would save?

I wonder how much trouble corrupt or no output will cause?

Markus M
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