[OpenLayers-Users] GeoRSS and layers

[Christopher Schmidt]

To the GeoRSS list: 

These questions came up on the OpenLayers users list, but they are
general questions on use of GeoRSS more than OpenLayers implementation
questions. If you have thoughts on the answers to these questions, I
would love to hear them. Please follow up to the GeoRSS list. 

Thanks.

On Mon, Jan 15, 2007 at 03:56:34PM +0100, Yves Jacolin wrote:
> Hi,
> 
> I would like to load a GeoRSS url with several channels. For each channel, I 
> would like a sp?cific layer in the layer control bar. But the actual geoRSS 
> javascript file load all items in one layer.
> 
> Do you have any ideas to modify the georss.js file to load one layer for each 
> channel nodes ?

Multiple channels in one RSS file is, as far as I'm aware, a violation
of the RSS specification. If you can point to a place where this type of
behavior is defined, we can investigate adding support for it.

If I were to implement it, I would probably simply add multiple layers,
one for each channel (and having multiple files to contain that data).
Is there a reason that doesn't work for you?


> Furthermore, do you know if it is "possible" to add an icon tags for example 
> to modify icons for each item ? I modified my georss.xml response to get 
> something like :
> <item>
>    <title>titre</title>
>    <link>link</link>
>    <description>Some description</description>
>    <geo:lat>48</geo:lat>
>    <geo:long>2</geo:long>
>    <icons>points.png</icons>
> </item>

This type of definitions is a misuse of the RSS format -- adding new
terms should be done in a seperate namespace. At the moment, there is no
standardized mechanism for describing visualization of GeoRSS data. 

Rather than making something up and supporting it in OpenLayers, I would
like to see a general consensus on what is 'acceptable'. Personally, I
would rather see reuse of the KML specification's visualization
techniques, which I would be happy to support in OpenLayers. If a
general consensus is reached -- or even if a specification is created
and documented, such that future users can look up how to include
styling/visualization information into their GeoRSS feed by looking at a
web page -- I would be much more comfortable than with an ad-hoc
implementation.

> And copy-paste the part where icon is loaded from the test.js file. Does 
> GeoRSS allow to add its own tag ?

There is no GeoRSS support for changing the markers built into the core. 
You can change the *default* Marker for OpenLayers, by modifying the
defaultIcon variable, similar to the code at the end of Marker.js:

http://trac.openlayers.org/browser/trunk/openlayers/lib/OpenLayers/Marker.js#L126

but I assume you want different icons per-location, which would require
support in OpenLayers that we do not currently provide.

I'm CCing this message to the GeoRSS list,
http://lists.eogeo.org/mailman/listinfo/georss , as discussion on this
topic is wider than the implementation in OpenLayers: The two issues at
hand are whether GeoRSS supports multiple channels per file, and whether
there is a standard definition for describing styling information for a
feature. If a consensus is reached, I will bring the conversation back
to the OpenLayers list. 

Regards,
-- 
Christopher Schmidt
MetaCarta