GeoWebCache and fractionalZoom: addin or feature proposal

[Marc Jansen-2]

Hi devs,

we develop an OpenLayers application that uses WMS-tiles generated by
GeoWebCache. But we have the need to allow fractionalZoom as well,
because the application will sometimes zoom to non-integer scales (when
we highlight search results, for instance). Without a change to the code
of OpenLayers these fractional zoomlevels mess up the map (because right
now GeoWebCache does not act as WMS when being asked for tiles it cannot
provide).

For the application in question we patched OpenLayers/Layer/WMS.js to
have an option to use a different baseURL when fractional zoomlevels are
needed. So when map.zoom is non-integer, we ask the original WMS-Server
for slow but correct tiles.

I am not sure whether this is possibly a addin, or an additional option
for WMS-layers. What do you think?

The code in question would introduce a new property
"alternativeFractionalZoomURL" (name of course TBD) to
OpenLayers.Layer.WMS-objects and one additional check in the
WMS.getURL-method (if the map allows fractional zoomlevels AND if the
alternativeFractionalZoomURL is not empty AND the current map.zoom is
fractional THEN use the altURL, behave as always in any other case).
Does this break code elsewhere? We did not have the time to run the
tests up until now, but maybe you see problems early at this stage.

Regards and thanks for any comments,
Marc

BTW: the new WMS.Post layer looks really promising! Great work!
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[Andreas Hocevar-2]

Hey Marc,

have you thought about a different patch, giving the map a "zoomstart"
or "beforezoom" event? You could then register for this event and call
layer.setURL with the WMS url when the zoom is fractional, and with the
GWC url when it is integer. This seems easier and more useful to me.

Just my 2¢
Andreas.

Marc Jansen wrote:

> Hi devs,
>
> we develop an OpenLayers application that uses WMS-tiles generated by
> GeoWebCache. But we have the need to allow fractionalZoom as well,
> because the application will sometimes zoom to non-integer scales (when
> we highlight search results, for instance). Without a change to the code
> of OpenLayers these fractional zoomlevels mess up the map (because right
> now GeoWebCache does not act as WMS when being asked for tiles it cannot
> provide).
>
> For the application in question we patched OpenLayers/Layer/WMS.js to
> have an option to use a different baseURL when fractional zoomlevels are
> needed. So when map.zoom is non-integer, we ask the original WMS-Server
> for slow but correct tiles.
>
> I am not sure whether this is possibly a addin, or an additional option
> for WMS-layers. What do you think?
>
> The code in question would introduce a new property
> "alternativeFractionalZoomURL" (name of course TBD) to
> OpenLayers.Layer.WMS-objects and one additional check in the
> WMS.getURL-method (if the map allows fractional zoomlevels AND if the
> alternativeFractionalZoomURL is not empty AND the current map.zoom is
> fractional THEN use the altURL, behave as always in any other case).
> Does this break code elsewhere? We did not have the time to run the
> tests up until now, but maybe you see problems early at this stage.
>
> Regards and thanks for any comments,
> Marc
>
> BTW: the new WMS.Post layer looks really promising! Great work!
> _______________________________________________
> Dev mailing list
> [hidden email]
> http://openlayers.org/mailman/listinfo/dev
>  

--
Andreas Hocevar
OpenGeo - http://opengeo.org/
Expert service straight from the developers.

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[Marc Jansen-2]

Hi Andreas,

hooking the changing of the URL to an appropriate event is a very good
idea. I didn't think about that. So maybe we'll change it that way
around. Yet this would mess up the map instantiation code a little bit
and I thought that having an option when generating the layer would be
more crisp.

Regards and thanks (your ¢ are very much appreciated :-)),

Marc


Andreas Hocevar schrieb:

> Hey Marc,
>
> have you thought about a different patch, giving the map a "zoomstart"
> or "beforezoom" event? You could then register for this event and call
> layer.setURL with the WMS url when the zoom is fractional, and with
> the GWC url when it is integer. This seems easier and more useful to me.
>
> Just my 2¢
> Andreas.
>
> Marc Jansen wrote:
>> Hi devs,
>>
>> we develop an OpenLayers application that uses WMS-tiles generated by
>> GeoWebCache. But we have the need to allow fractionalZoom as well,
>> because the application will sometimes zoom to non-integer scales
>> (when we highlight search results, for instance). Without a change to
>> the code of OpenLayers these fractional zoomlevels mess up the map
>> (because right now GeoWebCache does not act as WMS when being asked
>> for tiles it cannot provide).
>>
>> For the application in question we patched OpenLayers/Layer/WMS.js to
>> have an option to use a different baseURL when fractional zoomlevels
>> are needed. So when map.zoom is non-integer, we ask the original
>> WMS-Server for slow but correct tiles.
>>
>> I am not sure whether this is possibly a addin, or an additional
>> option for WMS-layers. What do you think?
>>
>> The code in question would introduce a new property
>> "alternativeFractionalZoomURL" (name of course TBD) to
>> OpenLayers.Layer.WMS-objects and one additional check in the
>> WMS.getURL-method (if the map allows fractional zoomlevels AND if the
>> alternativeFractionalZoomURL is not empty AND the current map.zoom is
>> fractional THEN use the altURL, behave as always in any other case).
>> Does this break code elsewhere? We did not have the time to run the
>> tests up until now, but maybe you see problems early at this stage.
>>
>> Regards and thanks for any comments,
>> Marc
>>
>> BTW: the new WMS.Post layer looks really promising! Great work!
>> _______________________________________________
>> Dev mailing list
>> [hidden email]
>> http://openlayers.org/mailman/listinfo/dev
>>  
>
>

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