[Benchmarking] Some styling comparisons at different zoom levels

[Andrea Aime]

Hi,
this morning I took some time to add a styling comparison at different
scales, just to make sure we're all rendering roughly the same map,
same layers, and that the scale dependent rules are triggering at the
same level for everybody.

The following reports what I've seen. Please double check and add
whatever I missed (and of course, if you're reading this a few
hours/days after it was sent, remember people are going to fix the
inconsistency so eventually we'll get all similar looking maps making
this mail irrelevant).

Also, remember the GeoServer ones have the actual scale as computed by
GeoServer on the bottom/right of the map, that is not available in the
other maps but does not count as a difference  ;-)

Differences visible at the 1:29k series
-----------------------------------------------------
- Constellation is missing the point labels and the ramps. That is not
Constellation fault, I just did not have the layer names for those
labels (I know, could have gotten them from the caps, but tried to
issue a request on the capabilities and I was still waiting after a
few minutes). So please, somebody just fix the links  :-) .
- The point labels do not have the same size across the servers and
not the same amount of halo, some do not at all. For GeoServer it's a
known problem that we should fix, we treat the pixel size of the font
as a point size instead. However looking at the labels I'm wondering
if we're all using the same font at all. This is something that was
not specified in the styling rules, which actually called for
something different (bold, color and size based on some attribute, but
without detailed specs, which nobody followed in the end).
I'm proposing to follow roughly what Mapserver did:
   - font has to be "Bitstream Vera Sans" (a TTF font everybody can
use, and it's available in svn:
http://svn.osgeo.org/osgeo/foss4g/benchmarking/mapserver/etc/)
   - size is 8 pixels
   - halo is 1 pixel radius, white
Please everybody check you're following these styling rules. MapServer
people too, I think you're not using that TTF font)

- The point label placement is not the same either. Shall we all use
label placement 0.5/0.5 (that is, centered around the point to be
labelled). GeoServer and Mapnik seem to be doing that.
- MapViewer is adding a red cross symbolizer on the left of some
labels. They are there at all scales, not going to repeat this comment
for the other scales. Should not be there afaik
- Constellation is not respecting proper cased road drawing. The road
ends do not merge but get one on top of each other instead (which
might be faster to render, or not, depending on how the rendering
engine works).
   This difference is there at all scales so I'm not going to repeat it
- Constellation and MapViewer are not using round line caps for the
road, track, ramp, highways (all roads in general) layers as others do
- Layer stacking is inconsistent between servers. I'm going to propose
a uniform order in a separate mail.

Differences visible at the 1:31k series
-----------------------------------------------------
All servers but Constellation switch off the contour, buildings and
industry layers.

Differences visible at the 1:49k series
-----------------------------------------------------
Constellation is missing the ramps (but at this scale contour,
buildings and industry are switched off like in the others)

Differences visible at the 1:51k series
-----------------------------------------------------
Constellation is missing the ramps


Cheers
Andrea
-- 
Andrea Aime
OpenGeo - http://opengeo.org
Expert service straight from the developers.