[mapserver-dev] RFC: GMaps API for mapserv

Christopher Schmidt crschmidt at metacarta.com
Fri Apr 11 06:47:00 EDT 2008


On Thu, Apr 10, 2008 at 09:48:27PM -0700, Paul Ramsey wrote:
> * If PARTIALS is not set in labeling directives, it will be turned on automatically.

This *only* makes sense with the PROCESSING=DONT_CLIP_ME_BABY or
whatever the option is: 'partials true' will only cause problems if you
turn it on without this. (PARTIALS defaults to TRUE: The processing
option does not.)

Is there a significant performance cost to the PROCESSING option?

I'm almost wanting to say that rather than do thsi (if it's not goign to
incldue the next step in this phase) it would be better to explicitly
set it to off. The reason is that any 'annotation' or point layers are
*not* going to be properly labeled across tiles with PARTIALS TRUE
without extra data being requested (I don't think?) because the data
that they're in will not be included in the spatial data requested from
the database. That is:


      ----------
      |        |
   *  |        |  
Chicag|o       | 
      |        |
      ----------

The point here will not be rendered in the right hand tile, so the label
will be missing an 'o'.

If we turn partials *off*, then all these cases 'go away' (at the cost
of fewer labels per tile in total.)

My suggestion is to actually reverse the state of the proposal: set
PARTIALS FALSE by default, and in the future, when more 'metatile like'
features are added, toss in PARTIALS TRUE and the PROCESSING option and
maybe a shield_cache_edge_buffer -5 metadata (to protect shields:
doesn't exist yet, same vein as label_cache_edge_buffer).

In the meantime, 'partials off' is likely to give you a better
experience (fewer clipped labels) in my experience, with the net result
being fewer labels in total... but usually in a way that works out for
the best in the end.

I think this API is the better way to go, and I'm now more in favor of
it.

I will also write OpenLayers documentation on how to pull these tiles
in, and update the 'spherical mercator howto' mapserver section that I
am currently maintaining for OpenLayers documentation purposes.

Regards,
-- 
Christopher Schmidt
MetaCarta


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