OS 2.0 Mapnik layer shifting

[edouard]

Hi,

It seems that in low resolutions (high levels of zoom so that houses/
streets are clearly visible), Mapnik layer tends to "shift" a little
when changing resolution.

The problem is visible in the "Global examples/Legal Information
Examples" from the demo for instance. There are levels of zoom in
which, when zooming in and out, the layer shifts. For example, It
occurs when the ScaleLine displays "1000m/500m" or "100m"...

I don't know if I made myself clear enough, but that problem didnt't
occur in version 1.2.1.

Regards,

--
Edouard

[Maxime Viry]

Hi,

It's a known issue due to freeZoom with tiled layers.

We are working on it.

Regards,
Viry Maxime

--
Edouard


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[Hermes David]

Hi,

I found how to fix the problem. the problem occurs as a consequence of 2 things:

   1) Wrong tile origin - the default value is Location(0,0, "EPSG:EPSG:4326"), but for OSM layers, it shoud be Location(-20037508.34, 20037508.34, "EPSG:900913")

   2) wrong min and max resolutions. - OSM layers should use as max resolution 156543.0339, but some code on FXLayer tries to reproject the default max resolution from "EPSG:EPSG:4326" to "EPSG:900913" generating diferent values and as consequence a minor shift on tiles, that intensifies as you zoom in and as you go more to west and south (farther  from tile origin). To fix this, just set the min and max resolutions to the correct values or simply override the methods to return resolutions[0] and resolutions[resolutions.lenght-1].

Regards,

Hermes David Junior

[Ossi Rönnberg]

I'm having this issue... my VectorLayer is shifting as you zoom in or
out.
I tried these values, but it just makes Mapnik disappear completely.

[Hermes David]

//this is my custom Mapnik class with the shift problem fixed.

package com.openscales
{
import org.openscales.core.basetypes.Resolution;
import org.openscales.core.layer.osm.OSM;
import org.openscales.geometry.basetypes.Bounds;
import org.openscales.geometry.basetypes.Location;
import org.openscales.geometry.basetypes.Pixel;

public class OSMapnik extends OSM
{

public function OSMapnik( name:String)
{
var url:String = "http://a.tile.openstreetmap.org/";
super(name, url);

this.altUrls = [ "http://b.tile.openstreetmap.org/",
"http://c.tile.openstreetmap.org/" ];
this.generateResolutions(18, OSM.DEFAULT_MAX_RESOLUTION);

this._tileOrigin = new Location(this.maxExtent.left,
this.maxExtent.top, this.projection);

}

override public function
getSupportedResolution(targetResolution:Resolution,
finest:Boolean=false):Resolution{
return super.getSupportedResolution(targetResolution, finest);
}

override public function get minResolution():Resolution{
return new Resolution(this.resolutions[resolutions.length-1],
this.projection)
}

override public function get maxResolution():Resolution{
return new Resolution(this.resolutions[0], this.projection);
}

}
}



//this is my custom FxMapnik, if you need to use

package com.openscales
{
import org.openscales.core.basetypes.Resolution;
import org.openscales.core.layer.osm.OSM;
import org.openscales.fx.layer.FxTMS;

public class FxOSMapnik extends FxTMS {
public function FxOSMapnik() {
super();
this.maxResolution = new Resolution(OSM.DEFAULT_MAX_RESOLUTION,
"EPSG:900913");
this.numZoomLevels = 18;

this._layer=new OSMapnik("");

[Hermes David]

And dont forget to set the map projection to "EPSG:900913", since
layers only appear if the map is in the same projection

[Ossi Rönnberg]

Nice, that did the trick!
I don't know what I tried wrong.

[Hermes David]

It works better if you skip broken zoom levels by setting

map.defaultZoomInFactor = 0.5;
map.defaultZoomOutFactor = 2;

[Ossi Rönnberg]

http://www.youtube.com/watch?v=LJFXHJDqd8c 

There is still strange difference between AIR and EMBED versions.

[diego]

Hi guys. I need Mapnik to be in EPSG:4326, but I'm not being able to do it. What would be the best way to accomplsh this? And I have the same issue with Bing.

Regards,

Diego