[QGIS-Developer] Vector tiles

[Tom Chadwin]

Hi Andreas


Andreas Neumann-4 wrote
> Areas in vector tiles are artificially cut into pieces. If you want to
> stroke the outlines of the areas you would not only get the wanted
> outlines of the original feature geometries, but in addition, also the
> unwanted, artificial, borders. 

Yes, so you buffer the tile during rendering, so that this "internal" stroke
falls outside the actual tile boundary, then clip back to the correct
dimensions.


Andreas Neumann-4 wrote
> And even if you just fill and don't stroke, you would get rendering
> artefacts (depending on the antialiasing settings of the rendering
> library). qt, for instance, does not a good job to avoid rendering
> artefacts of adjacent polygons who have a shared outline. You would
> still see fine white lines. 

Would require experiment, but since tile boundaries are always
horizontal/vertical, antialiasing issues should be less severe than
otherwise. Again, the buffer-then-clip approach above might result in a
non-antialiased tile boundary.


Andreas Neumann-4 wrote
> If you want to label areas, it would also be a problem. Similar
> problems, if you want to label LineString data. 

100% - labelling is problematic, but an approach is to label all fragments
of features, and rely on label collision settings to produce workable
output.


Andreas Neumann-4 wrote
> There just so many unsolved issues with vector tiles (if they aren't
> connected properly back to the original geometries by the client) - that
> personally I don't bother working with them. 

Sure, but many do work with them.

I guess the points you raise might make the plugin approach the right one -
I was just aware of the OGR work, so I thought it should be investigated. At
the end of the day, vector tiles exist, and do render correctly in other
clients.

Thanks for all the info

Tom




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