On Thu, Nov 16, 2017 at 10:02 PM, Markus Neteler <[email protected]> wrote: > > On Wed, Nov 15, 2017 at 10:03 PM, Markus Metz > <[email protected]> wrote > > On Wed, Nov 15, 2017 at 4:35 PM, Markus Neteler <[email protected]> wrote: > >> > >> On Wed, Nov 15, 2017 at 3:49 PM, Markus Metz > >> <[email protected]> wrote: > >> > On Wed, Nov 15, 2017 at 1:36 PM, Helmut Kudrnovsky <[email protected]> > >> > 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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