[OpenLayers-Dev] Developement of an external vector symbol

[Barbara Philippot]

Thanks for your advice Cameron!

    I researched available tools to transform SVG into VML. I found that
only one project was usable without too many modifications : Mark
Finkle's opensource project : Implementation of simple static SVG
rendering in Internet Explorer using VML, which is under the terms of
MIT license.

http://starkravingfinkle.org/blog/2006/03/svg-in-ie/

    After a certain number of modifications (symbol and viewbox
management, minor corrections), I was able to transform SVG symbols into
VML groups. Some problems are still there but most of them are well
transformed. So, I inserted the needed functions into Openlayers
codebase. For the moment, they are independant functions put into VML.js
(one main function and 4 linked functions).
    We need to put these functions elsewhere : methods still in VML.js,
in Util.js?, or integrate them into a new class and a new file?

Since VML shapetype elements can't be as complex as SVG symbol elements,
I transformed SVG symbols into VML groups with a visibility put to
hidden. The specified group matching the point to draw is then cloned,
made visible and put at the right place.

So when creating a new vector layer, we can now specify an option with
the URL of a single SVG symbols library which will be loaded in the
rendererRoot node. Symbols of this library can be used on Firefox
(directly in SVG) or on IE (transformed on the fly in Javascript into
VML). It slows a little the browser down but loading time is satisfactory.

For the moment, we have used this catalogue :

http://wiki.openstreetmap.org/index.php/Osmarender/Symbols

but people can add their own symbols or symbols from the Open Clip Art
library provided that SVG symbols are put inside a <symbol> element with
the correct viewBox attribute associated.


See :
http://dev.openlayers.org/sandbox/camptocamp/vectorSymbols/examples/vector-symbols.html



Regards,

Barbara


Cameron Shorter a écrit :
> Barbara,
> This sounds like a great initiative and I'd be surprised if there
> isn't already a number of projects which transform between SVG and VML.
> I know that there has been work converting GML to SVG, and hence there
> shouldn't be much work transforming GeoRSS to SVG.
>
> So I suggest:
> 1. Before you do any development, research available tools that you
> can use.
> 2. Create one vector library (either SVG or VML) and use a translation
> tool to automatically convert from one to the other.
> 3. Precompile the alternative library. Ie, don't convert SVG to VML on
> the fly in Javascript. It will slow the browser down.
> 3. I suspect that SVG would be a better format to support than VML. I
> believe SVG is used by a number of other projects, eg the Linux Icon
> libraries.
> 4. Search for existing icon libraries and consider extending the
> existing icon libraries rather than creating a new project. Maybe make
> a geographic version of the library.
> 5. Think bigger than just OpenLayers. You start the free icon library
> used by all Open Source GIS projects. It might be a candidate project
> for: http://wiki.osgeo.org/index.php/OSGeo_Labs
> (Although you may want to seed your project within Openlayers)
>
>
> Barbara Philippot wrote:
>> Ian Mayo a écrit :
>>  
>>> Barbara,
>>> I'm afraid I can't offer an opinion on your languages challenge.  It
>>> would be great if there was a pre-existing file-format for vector
>>> symbols, then we just specify filenames rather than hard-code the
>>> vectored shapes.
>>>       
>> Yes, this is why we are trying to do. But people would have to specify
>> two filenames (one in SVG, the other in VML) to replace the pre-existing
>> symbol catalogue files and it's not still the ideal solution but perhaps
>> it's the only one.
>>  
>>> I'm currenlty working on provision of per-entry icons (images) for
>>> georss feeds. [1].  I've made good progress, but may have to pause my
>>> efforts for the next 7 days, see my demo at: [2].   Had you considered
>>> using the symbols on a per-entry fashion in a georss feed?  I suspect
>>> it's fortunate I've got a self-induced development pause: it would
>>> seem to be worth offering per-entry symbols as well as icons.
>>>
>>> Appreciate your thoughts/opinions.
>>>       
>> Well, I hadn't considered using symbols in a georss feed and I don't
>> know well Georss format. For the moment, symbols are associated with
>> points geometry with a style.use="symbol" in the same way as images were
>> associated with style.externalGraphic. So, I haven't looked in detail to
>> the way you attach icons to GeoRss nodes but it seems that you would be
>> able to use SVG and VML symbols as well as images.
>>
>> I hope to make progress before your development pause ends :-)
>>  
>>> Ian.
>>>
>>> 1. http://trac.openlayers.org/ticket/1073
>>> 2.
>>> http://dev.openlayers.org/sandbox/ianmayo/branches/rss/openlayers/examples/georss.html
>>>
>>>
>>>       
>>
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>
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