[OpenLayers-Users] IE strategies

[Yves Moisan]

> Hi, setting dynamical ratio has proven quite usefull to me...something like:
> 
> var strategyBBOX = new OpenLayers.Strategy.BBOX({ratio:1.4});
> 
> map.events.register('zoomend', map, function(e){
>             zoom = map.getZoom();
> //calculating ratio depending on zoomlevel, based on what u need
>             var ratio = zoom/4.0+0.75;
>             if(ratio<1.4)ratio = 1.4;
> 
>            //im not sure which one has to be set excatly
>             strategyBBOX.options.ratio=ratio;
>             strategyBBOX.ratio=ratio;
> ....
Hi Ivan,

Seems to me like this buttresses what I'm saying in my previous answer
to Andreas e-mail : the issue is worse for maxfeatures small AND (if I
use your trick) the zoom level is high.  Suppose you setCenter on a
feature with a high zoom level (e.g. 16), then you get ratio = 4.75.
The probability that I end up with a number of clustered features <
maxfeatures grows with zoom level ! If I ask for 2 features at a zoom
level of 20, I may get nothing in my viewport.  Could be rather
puzzling.

Thanx for sharing your trick.

Yves
> ....
> hope it helps,
> ivan
> 
> On Fri, Jan 9, 2009 at 11:52 PM, Andreas Hocevar <ahocevar at opengeo.org> wrote:
> > Yves Moisan wrote:
> >>> My bad. It should read
> >>> new OpenLayers.Strategy.BBOX({invalidBounds: function(){return true;}})
> >>
> >> Well, I was dumb enough to stick it in the Cluster() strategy of my
> >> 2-strategy layer on my side of the story :-(.  At any rate, I can
> >> confirm that an XHR is done on zoom in now.
> >>
> >> I still have issues though.  One peculiar thing is that for some reason
> >> the BBOX issued by OL to the server is consistenly larger than the one
> >> specified in map.zoomToExtent.  Here are numbers (HTML =
> >> map.zoomToExtent(new OpenLayers.Bounds()); and "Output BBOX" is sent out
> >> to the server) :
> >
> > See the ratio property of the BBOX strategy. You may want to set it to 1
> > (the default is 2, which means it will request a bbox twice as large as
> > the viewport).
> >
> >> There are also issues with the masfeatures parameter : a small number of
> >> maxfeatures might bring in less features than maxfeatures even though
> >> the number of features definitely is more than maxfeatures.  To
> >> illustrate results comparing BBOX alone and Cluster, see :
> >>
> >> http://www.flickr.com/photos/30818159@N05/3182451399/ shows BBOX +
> >> Cluster (maxFeatures = 200) on the left and BBOX alone on the right.
> >> Both return 101 features.  Good
> >>
> >> http://www.flickr.com/photos/30818159@N05/3182451587/ shows BBOX +
> >> Cluster maxFeatures = 200 on the left (results in 101 features) and
> >> maxFeatures = 10 on the right (results in 9 features ???).  There
> >> clearly should be 10 features returned.
> >
> > This obviously has to do with the ratio property mentioned above:
> > maxFeatures applies to the bbox requested from the server, which is
> > twice as large as the visible viewport (if using the default ratio of 2).
> >
> > Regards,
> > Andreas.
> >
> > --
> > Andreas Hocevar
> > OpenGeo - http://opengeo.org/
> > Expert service straight from the developers.
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> >