[OpenLayers-Users] Map reprojection issue

[Jean-François Gigand]

Hi Hugo,

I can't answer your question straightforwardly, but can give some hints.

- map.projection is only used as the default for new added layers
  The reference is map.getProjectionObject() which returns cloned baseLayer's.

- same for maxResolution and minResolution: they matter for the layers,
  not for the map. The baseLayer is the master.

- the 'changebaselayer' event is triggered after the change was made effective,
  so the map.getCenter() in your function would return the new center
  (within the projection of the new baseLayer's projection)

- the OpenLayers.Map's setBaseLayer() function does not seem,
  indeed, to take care of reprojecting the map center.
  As a workaround, you may either :
     - reproject the current center *before* calling setBaseLayer()
       and affect it to map.center
     - make your own Map class extending OpenLayers.Map
       and overload setBaseLayer to handle the reprojection
       (either replacing the implementation, or just reproject this.center
       before calling OpenLayers.Map.prototype.setBaseLayer)

I recommend your to dive into OpenLayers' source code, which is the
best way to really understand how it behaves, for complex problems
like this one.

Best regards,

Jean-François Gigand - Geonef
Paris, France - http://geonef.fr/




2011/8/12 Hugo <hfpmartins at gmail.com>:
> Hello all,
> I'm trying to reproject openlayers map according to the selected base layer.
> So, when the app is loaded my map has the EPSG:900913 projection (so that i
> can use OSM, google, etc). I have other base layers that are in the EPSG:
> 3763 projection and, when the user activate this layers the map will
> automatically reproject itself to this new definition. I was able to
> accomplish this however i have a small bug that i've not been able to
> correct until the moment. After reprojecting i can't pan and if i make a
> zoom it will go to a strange location (i think the zoom is still assuming
> the old coordinates). After making the zoom i'm able to pan and zoom
> normally.
> The code i'm using:
> function onBaseLayerChange(evtObj){
>    var mapProj, baseProj, map, newBase, reproject;
>    map = this;
>    newBase = evtObj.layer;
>    mapProj = (map.projection && map.projection instanceof
> OpenLayers.Projection) ? map.projection : new
> OpenLayers.Projection(map.projection);
>    baseProj = newBase.projection;
>    reproject = !(baseProj.equals(mapProj));
>    if (reproject) {
>       var center, maxExt;
>       center = map.getCenter().transform(mapProj, baseProj);
>       maxExt = newBase.maxExtent;
>       map.projection = baseProj;
>       map.resolutions = newBase.resolutions;
>       map.maxResolution = newBase.maxResolution;
>       map.minResolution = newBase.minResolution;
>       map.maxExtent = maxExt;
>       map.restrictedExtent = newBase.restrictedExtent;
>       map.setCenter(center);
>    }
> }
> I suppose i'm not setting some property... but which one?
> Thanks in advance.
> Cheers,
> Hugo
>
> --
> Hugo Martins
> LabNT - ISEGI UNL
> Campus de Campolide
> 1070-312 Lisboa
> N 38°43'56.84", W 9°9'35.74"
>
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