[OpenLayers-Users] Performance?

[Erik Uzureau]

On 8/16/06, Jeff Dege <jdege at korterra.com> wrote:
>
>   ------------------------------
> *From:* Erik Uzureau [mailto:euzuro at gmail.com]
> *Sent:* Tuesday, August 15, 2006 8:59 PM
>
> *To:* Jeff Dege
> *Cc:* users at openlayers.org
> *Subject:* Re: [OpenLayers-Users] Performance?
>
>  Hi Jeff,
>
> Are you running on 1.0 version or on the svn HEAD?
>
> I'm running svn HEAD, as of a week or so ago.
>
>
> We just put a bunch of new funky gridding stuff into the trunk, like
> reusing divs, adjustable tile-buffer, and spiral gridding.
>
> I just did an svn update, and I can see the changes you're talking about.
>
>  To modify the off-current-view tiles, try fiddling with the 'buffer'
> property in Grid.js -- ex:
>
>         function init(){
>             map = new OpenLayers.Map( $('map') );
>             layer = new OpenLayers.Layer.WMS( "OpenLayers WMS",
>                     "http://labs.metacarta.com/wms/vmap0", {layers:
> 'basic'},
>                     { tileSize: new OpenLayers.Size(800,475),
>                       buffer: 1 });
>             map.addLayer(layer);
>
>             map.setCenter(new OpenLayers.LonLat(lon, lat), zoom);
>             map.addControl( new OpenLayers.Control.LayerSwitcher() );
>         }
>
>
> The default is set to 2 but you can take it down to 1 (as above) and that
> will probably
> speed things up for you, though UI-wise it might be less sweet.
>
> I think it's an inherent trade-off.  Faster initial load vs. faster
> panning after the initial load.  Though if you're loading tiles in a spiral
> from the center, and the UI remains responsive while the non-visible tiles
> are still loading, you might be achieving the best of both worlds.
>
> Are you spiraling within each layer?  Or for all layers?
>
> That is, is it:
>
>   for each layer
>       for each tile, starting at the center and spiraling out
>         draw the layer's tile
>

it is this one (the former). the latter admittedly would
be pretty cool... but given our current architecture, it
would be practically impossible to pull off... .

e




or is it:
>
>     for each tile, starting at the center and spiraling out
>       for each layer
>         draw the layer's tile
>
> ???
>
>  Note that setting the buffer to 0 will not work.
>
>
> So yeah, the reason you are seeing so many tiles loaded is because it is
> loading a buffer
> of two tiles around the viewport. Also, the reason you dont see simple
> numbers like 9
> and 25 is because of the way we have implemented gridding -- with cacheing
> in mind, OL
> uses a sort of world-grid at each zoom level, which means that specifying
> a tile size of the
> same size as the viewport won't necessarily (in fact quite unlikely) mean
> that it will load one
> tile smack-dab in the center of the viewport. Does that make sense?
>
> --Erik
>
>
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