[OpenLayers-Users] XML / GeoRSS / GML / KML and combined layers (Markers & SVG)

[mike]

Thanks for this.  I think a wiki page comparing these various XML type
formats with links to various examples eould be extremely usefull - for me
at least!

I've had a go at creating this - probably entirely incorrect but perhaps you
could correct / add to this?  I've marked things with ??? where I am unsure
about something or examples seem to be broken or where a simple change would
improve the usefulness of the example considerably.

http://trac.openlayers.org/wiki/XML

I don't want to blunder in and mess up your wiki, but I think maybee a main
'features' or 'overview' page would be good linking from the documentation
page - http://trac.openlayers.org/wiki/Documentation which could then link
to things such as this  XML page


On 19/09/2007, Christopher Schmidt <crschmidt at metacarta.com> wrote:
>
> On Wed, Sep 19, 2007 at 10:43:33AM +0100, mike wrote:
> > Hi,
> >
> > Is there any documentation of the merits / purpose and intended future
> > developments of the various XML layers such as GeoRSS, GML, KML etc?
>
> Well, the versions in 2.4 were very minimal: Primarily designed to get
> people started. Specifically, KML had no polygon support, and was
> readonly, GeoRSS was write only, etc. The resutl of this, however, was
> that in 2.5 we got both of those fixed: GeoRSS is now a full Atom/RSS
> GeoRSS Simple parser, KML supports all KML 2.1 Geometries, etc.
>
> I have no idea if our GML parser is *valid*, but it has always been the
> most complete, I believe because its development was funded as part of
> Cameron Shorter's OWS Testbed work. (I could be wrong on this.)
>
> > They seem to be very similar and almost interchangable, and I'm
> > finding this a bit confusing.
>
> Some day in the distant future, when OpenLayers does everything you need
> and new features are just a memory, all Vector Formats will have a
> complete mapping of their formats into OpenLayers constructs as best as
> the client is able. (This does mean that there are many things that they
> will be missing -- For example, we will not be representing the altitude
> of KML features in OpenLayers, so far as I can predict.)
>
> At the moment, they are as complete as people have wanted to make them,
> and no more. In some casees (GML, via OGC, and soon I believe KML via
> the OWS-5 work), specific Formats have gotten a boost due to outside
> funding of development, thus they may be more complete. In other cases
> (GeoJSON) the spec is relatively complete and simple in and of itself,
> and the authors of the spec happen to be OpenLayers contributors.
>
> > For example, I'm using GeoRSS to draw markers, and KML to draw lines.
> > However, this excellent GeoRSS Serialise example seems to be an edit /
> > draw component for lines and polys:
> >
> http://dev.openlayers.org/sandbox/ahocevar/sldRenderer/examples/georss-serialize.html
>
> There's actually probably no reason that you *have* to use GeoRSS to
> draw markers anymore: it could be done with just a little bit of styling
> work on a vector layer. It's not trivial yet, because there is no
> pressing business case telling me why I should do it, and presumably no
> one else has had one either.
>
> > Equally, KML boasts support for styles, although this is not
> > implemented yet, and if we are accepting the Google definition, then
> > KML should support both markers and lines / polys.
>
> I'm assuming when you say "KML boasts support", you don't mean within
> OpenLayers, but in general. If we accept that, we should also support
> Photo Overlays and 3D. We can't do that :)  However, mapping the full
> set of KML data that *can* be represented into OpenLayers is the
> eventual goal: just not neccesarily a high priority.
>
> > Is there a twiki page for this or a good resource I could refer to?
> > I'm considering developing this further and I'd like to make sure I'm
> > doing the right thing before I start...  Also if anyone if actively
> > developing in this area I'd be very interested to discuss and see if I
> > can help.
>
> Not really. Docs are the weakest point on the project, but if you have
> specific questions I'm glad to answer them, and you can turn them into a
> wikipage. Also, I'm often on IRC, irc.freenode.net, #openlayers, as are
> 40+ other extremely intelligent contributors to the project, many of
> whom would be glad to help.
>
> > My other point is about combined layers - I'd like to create a layer in
> the
> > layerswitcher which shows markers and lines / polys (i.e. SVG I
> assume).  Is
> > it possible to make a combined layer or wrap two layers into one in some
>
> > way?
>
> Several. But it's likely that you just want to use a Vector layer with
> an externalGraphic: see the vector-features.html page for styling
> examples. (The only time this wouldn't be true is if you were required
> to support Safari 2.)
>
> Regards,
> --
> Christopher Schmidt
> MetaCarta
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