[mapserver-dev] Vector Tile Production...

[thomas bonfort]

Thanks for having a look Even,

> It raises a few interesting ideas for having a more generic scale-aware WFS
> mode. Perhaps we could have vendor WFS options WIDTH and HEIGHT that, if set,
> would trigger the msCalculateScale() call. So that could also potentially be
> used to have scale-aware shapezip output ("give me features in this AOI
> appropriate for a 1024x1024 rendering")

That would be useful, but I'm unsure about the implications if those
vendor params are left out of the request. The two use-cases I want to
address for vector tiles are

LAYER
  GROUP "roads"
  NAME "roads-far"
  MINSCALE 1000000
  DATA "the_geom from roads_simplified where type='motorway'"
END
LAYER
  GROUP "roads"
  NAME "roads-close"
  MAXSCALE 1000000
  DATA "the_geom from roads"
END

and

LAYER
  NAME "roads"
  MINSCALE 1000000
  DATA "the_geom from roads_simplified where type='motorway'"
END
LAYER
  NAME "roads"
  MAXSCALE 1000000
  DATA "the_geom from roads"
END

I haven't tested these, and don't know how the WFS implementation will
react when the TYPENAME given corresponds to a mapfile GROUP or to
multiple identically named layers. (There might be a few more tweaks
to add in my patch to handle these). A WFS getfeature query without
vendor-params on these examples would have to decide on which layer(s)
it has to operate.

> And the clipping to the BBOX could also potentially be a CLIPPED=YES vendor
> option (but you have to do it anyway for MVT output due to the way coordinates
> are encoded).
Might be nice to have, but not really related to vector tiles (as in
that case the clipping *must* be done even if the vendor option is not
set). Also, the current implementation clips features in "pixel"
space, i.e. after reprojection and scaling has occured.

Regards,
Thomas