On Wed, Jan 16, 2013 at 6:05 PM, David Winslow <dwins...@opengeo.org> wrote:
> Hi all (mostly Andrea though),
>
> I've been asked to look into making some KML improvements, so it seems
> that Andrea and I should coordinate a bit to avoid potential clobbering.
> I'm still just in the planning phase and probably won't be making KML
> changes in GeoServer soon (in the next few weeks.)
>
The KML refactor will probably happen in a separate module as Justin
suggested, and it's not going to start
right away either, need to formulate a plan that everybody is happy with
before start to work on it.
This week is hectic enough with the impending feature freeze for 2.3.x,
hopefully the discussion will
resume next week.
>
> The improvements I'm talking about would relate to giving more faithful
> representations of PointSymbolizers in KML generated by GeoServer.
> Currently GeoServer discards most aspects of Marks (only fill and opacity
> are preserved) and does not always ensure that URLs included in KML will
> represent resources that are accessible to remote clients. Additionally,
> GeoServer encodes an SLD style with multiple PointSymbolizers into a KML
> Style with multiple IconStyles, which is invalid. (Google Earth will render
> these, but discards all but the last IconStyle.)
>
> Anyway, to resolve these issues I'm thinking about adding facilities to
> GeoServer for rendering individual icons for use in KML - both as a REST
> service for actual KML files and also as embedded files in KMZ. The
> KMLVectorTransformer would need to be modified to leverage these utilities
> as well. So I'm interested to try and formulate a plan that allows these
> new features to be developed without impeding or being impeded by the
> refactor.
>
Hum, I don't see the two actually colliding too much as long as these
utilities are well incapsulated,
something taking a feature and a point symbolizer and returning back a
BufferedImage, then
it's up to the the KML code to just call them when dealing with a point
symbolizer which is
not already an external reference to a web accessible resource.
This restful symbol service you're talking about is what I was envisoning
myself as well for
the task (something that was discussed in the past as well), I'm wondering
what you
are going to do for symbolizers that are depending on feature attributes,
and also on how
the symbol definition is moved around?
Generically speaking, in order to draw an icon you need the feature, with
its attributes,
and the set of symbolizers that make up the symbol: a rule can contain
many, and to build
complex symbols it's not uncommon to end up using more than one, see for
example
the POI style for a trivial example.
Now, the KML generated can be downloaded, to keep it stable it would be
great if
the URL referring back to the server contained the full definition of what
needs to be
done... however the SLD can be very large (multiple symbolizers) and might
not fit
into a normal URL. Also the size of the feature attributes can be
completely unpredictable
(what if one of the attributes is a large text? unlikely, but not
impossible).
An option could be to compress the data and base64 encode it, but it would
get you
only so far.
Another option is instead to refer to the SLD and the feature, something
like:
&rule=poi/0/0&layer=poi&featureid=poi.1
Where:
* poi/0/0: the first rule in the first feature type style in the poi style
* layer: the layer where the feature is coming from
* featureid: the id of the feature
This is compact, but has drawbacks too:
* not stable over time, the layer can go, the feature can disappear
* assumes the feature does have a stable identifier, but read only layers
can
also lack a primary key
Hmm... interesting problem :-)
Cheers
Andrea
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