[OpenLayers-Users] WMS in OpenLayers: Objects get Cut

[Tim Schaub]

Pfirter Lukas wrote:
> Hi list,
> I have a UMN mapserver setup that I try to access with OpenLayers.
> I can get the objects and it displays the PNG images for them in OL. But 
> these objects don't seem to get repeated over multiple mapserver 
> pictures (meaning I see an objects, for example a train station symbol 
> and the half of its description. The other part of the description 
> should be in the next image receieved from the mapserver, but I don't 
> see it). Google Maps under my WMS layer works fine.
> 
> What could be the problem? Does OL get wrong images from the mapserver? 
> Or is the grid from the mapserver images setup wrong?

Each request to a WMS for an image tile is independent.  When you you 
request a tile from MapServer with bounds that contain your train 
station (point), MapServer will render as much of that symbol as it can 
on that tile.  When you request the next tile that doesn't contain the 
train station (point), MapServer has no reason to render a partial train 
station.

You can get around this in two ways:
1) use something that requests larger tiles with a buffer, slices them 
up in to smaller tiles and discards the buffer - see http://tilecache.org

or

2) use the "gutter" property on your WMS layer in OpenLayers - see
http://dev.openlayers.org/docs/files/OpenLayers/Layer-js.html#OpenLayers.Layer.gutter

# ignore a 10 pixel gutter around each tile
var layer = new OpenLayers.Layer.WMS(name, url, params, {gutter: 10});

Good luck,

Tim


> 
> Are there settings in OpenLayers for this?
> Thank you.
> 
> 
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