I was traveling so could not respond. So sorry to chime in a bit late. For me it was a bit counter intuitive that polygons with null attributes became zero in the finished raster. What if I had attributes with zero value in it?
I liked the idea of issuing a warning and using the `where` parameter. Anyway, thanks for the help and fix Cheers Daniel On Fri, Nov 1, 2019 at 12:33 PM Micha Silver <tsvi...@gmail.com> wrote: > > On 01/11/2019 9:38, Markus Metz wrote: > > > > On Fri, Nov 1, 2019 at 12:11 AM Veronica Andreo <veroand...@gmail.com> > wrote: > > > > Hi Micha > > > > El jue., 31 oct. 2019 a las 22:36, Micha Silver (<tsvi...@gmail.com>) > escribió: > >> > >> > >> On 31/10/2019 22:20, Markus Metz wrote: > >> > >> > >> > >> On Tue, Oct 29, 2019 at 7:40 PM Veronica Andreo <veroand...@gmail.com> > wrote: > >> > > >> > Hi Daniel, > >> > > >> > I agree that if there's a NULL in the column, there should be NULL in > the resulting raster. I suggest to open a ticket here: > https://trac.osgeo.org/grass/ > >> > >> easy solution: v.to.rast where="<attribute_column> is not null" > >> > >> or the new PR #173 > >> https://github.com/OSGeo/grass/pull/173 > >> if an attribute value is null, the corresponding vector features will > not be rasterized > >> > >> Markus M > >> > >> I'm not sure I agree with the approach that a polygon with missing > attribute should become NULL. In my view, NULL should be used only for > pixels not covered at all by any polygon. > > > > but in the resulting raster (in rasters in general), there's no > difference, it's rather NULL or it has a value... it does not matter if the > null comes from areas originally covered by a polygon or not... > > I think it depends on the particular use case if it matters where a NULL > raster value comes from: a polygon with empty attribute or no polygon at > all for that cell. > > >> > >> Perhaps an additional input parameter "missing_attribute" so the user > can choose a value to enter into the raster if the attribute is missing. If > no parameter is supplied, and the chosen attribute column has missing > values, I'd prefer that the script exit gracefully, with a message that a > "missing_attribute" value is required. > > This can easily be done with existing tools: > - convert only those polygons with a valid attribute value: v.to.rast > where="attribute is not null" > - replace missing attribute values with a valid value: v.db.update > where="attribute is null", then v.to.rast > > I'm changing my PR to issue a warning if empty attribute values are found > and replaced with zero. > > > IMHO, that's probably the best way to deal with this. > > > > Markus M > > > > > yes, this could be a solution to keep track of where you had polygons, > but then you would need to use r.null anyway, no? I try to think of use > cases in which one uses a vector attribute to convert to raster, but then > still needs to know where the polygons were... because, for example, to > query a raster map with another raster map representing zones one would > convert the vector of polygons using cat and not an attribute, no? > > > > cheers, > > Vero > >> > >> > >> > El jue., 24 oct. 2019 a las 14:40, Daniel Victoria (< > daniel.victo...@gmail.com>) escribió: > >> >> > >> >> Hi list, > >> >> > >> >> I have a vector polygon map that I'm converting to raster. The > attribute column that I process has some empty rows (no data / null). When > I run v.to.rast, these empty rows become 0 (zero) on my resulting raster > map. > >> >> > >> >> Shouldn't v.to.rast respect the empty attribute table and create > null values for those polygons? > >> >> > >> >> For now I'll use r.null to fix this problem. But what if 0 is a > valid value? > >> >> > >> >> Cheers > >> >> Daniel > >> >> > >> >> PS - Running Grass 7.6.1 on Ubuntu > >> >> _______________________________________________ > >> >> grass-user mailing list > >> >> grass-user@lists.osgeo.org > >> >> https://lists.osgeo.org/mailman/listinfo/grass-user > >> > > >> > _______________________________________________ > >> > grass-user mailing list > >> > grass-user@lists.osgeo.org > >> > https://lists.osgeo.org/mailman/listinfo/grass-user > >> > >> _______________________________________________ > >> grass-user mailing list > >> grass-user@lists.osgeo.org > >> https://lists.osgeo.org/mailman/listinfo/grass-user > >> > >> -- > >> Micha Silver > >> Ben Gurion Univ. > >> Sde Boker, Remote Sensing Lab > >> cell: +972-523-665918 > > -- > Micha Silver > Ben Gurion Univ. > Sde Boker, Remote Sensing Lab > cell: +972-523-665918 > > _______________________________________________ > grass-user mailing list > grass-user@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/grass-user
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