[OpenLayers-Dev] Re: [OpenLayers 3] code sprint summary, and request for comments

[Eric Lemoine]

On Saturday, October 2, 2010, Bouiaw <bouiaw at gmail.com> wrote:
> Hi guys,

Thanks for jumping in Sébastien.


> I am really interested by this discussion, since we discussed a lot on
> that on OpenScales side too. I think it could be interesting to share
> what we have implemented in 1.2 and what we plan to do in 2.x, since
> we have the same starting point (OpenScales 1.0 = OpenLayers 2
> behaviour).
>
> We are also very interested by some feedbacks, in order to know if
> what we have done could make sense, or not, in OpenLayers. We may be
> be interested to backport it in an OpenLayers 3 fork on GitHub if
> there is some interest.
>
> About previous discussion, I think Paul Spenser proposal is great.
>
> The behaviour we have on OpenScales 1.2 is the following :
>  - Layer has no more isBaseLayer property
>  - baseLayer is just a reference to a Layer (could be any layer),
> stored in the map, in order to identify the current baseLayer
>  - baseLayer define current projection, reolutions and extent
>  - map has no projection, no resolutions, and use active baseLayer values
>  - No more overlays, all layers have the same capabilities

Is the base layer always below the other layers?


> Source code :
> http://bitbucket.org/gis/openscales/src/tip/openscales-core/src/main/flex/org/openscales/core/Map.as
> http://bitbucket.org/gis/openscales/src/tip/openscales-core/src/main/flex/org/openscales/core/layer/Layer.as
>
> For 2.x, we plan to implement free zoom mode and make resolution level
> optional (not anymore in Layer, but deeper in inheritance tree). The
> main "issue" we want to fix is the strong link between cached raster
> layer resolution levels and display zoom levels. We will remove this
> strong link, allowing the user to display any intermediate resolution
> (continous zooming) and use raster scaling on client side to display
> the closest raster cache level.
>
> Consequences of theses changes are the following :
>  - No more baselayer
>  - No more resolutions array or numZoomLevel in Layer class
>  - We create a new DiscreteLevelLayer class with resolutions array,
> numZoomLevel and related stuffs
>  - Map have a projection property, that is used to define the display projection
>  - Layer have a native projection property, and an information that
> allow us to know if we can request data in another projection (server
> ide reprojection)

Any reason for having layers advertize "primary" and "secondary"
projections? Why wouldn't a list of projections work for you?

Do you really have no baseLayer anymore? With a Google layer, or any
other DiscreteLevelLayer layer, how does the map know it should get
resolutions from that layer if it's not a base/master layer from the
map's perspective?

> Any feedback about these 2 behaviours applyed to OpenLayers 3 ?
> Do you think free zoom mode based on client image scaling could make
> sense in OpenLayers ? Is there some technical blocking points ?


Do you know OpenLayers' fractionalZoom implementation? (I'm sure you
do.) Do you have any issue with this implementation, making you
contemplating other implementations? I rmyself really should go ahead
a study the fractionalZoom implementation...

Thanks again, it is nice the see the OpenScales and OpenLayers teams
having design discussions together.

-- 
Eric Lemoine

Camptocamp France SAS
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