[GIS] Generate MaxScaleDenominator in geoserver

geoservergeowebcachewms

My geoserver is providing few overlayers with specific informations such as poi's or fire-hydrants. I'm using scale dependent styling, so it's not rendering this features above specified scale, but it still tries to render it and returns empty tiles. I've found WMS 1.3.0 includes MaxScaleDenominator and MinScaleDenominator tags, which can be provided in the getCapabilities result to show the optimum visualization ranges for each layer. I want to use it to learn my application not to ask about tiles above specified scale (cause they're empty there) so it will improve performance and reduce bandwidth usage.

I searched all geoserver properties (general, layer, caching) and I was not able to find any place to set this feature up, so I don't think there is some place in web-gui (or there is??), but maybe there is some resolution to write it somewhere in configuration files?

This is some link to my geoserver, e.g. layer is osm:Hydranty_active

After some investigation I've found that in layer osm:Hydranty_active served by WMS this information is included, but the same layer served via gwc don't have it, so trouble will be with GWC not Geoserver

Best Answer

The scale limits which are used in SLD should be converted automatically into MinScaleDenominator/MaxScaleDenominator with WMS 1.3.0 and into ScaleHint in WMS 1.1.1. You can read examples from this demo server:

http://demo.opengeo.org/geoserver/wms?service=WMS&request=GetCapabilities&version=1.3.0

http://demo.opengeo.org/geoserver/wms?service=WMS&request=GetCapabilities&version=1.1.1

Scale range hints are per layer and they are included into the document if there is some scale range that does not display a layer with any style that is attached to the layer. If you have a special rule for fire hydrants on a general poi layer (draw capitals at all scales but use MaxScaleDenominator=20000 for fire hydrants) it is not possible to read the fire hydrant's scale range from GetCapabilities. However, it is possible to get that information by downloading the whole SLD with the GetStyles request

http://demo.opengeo.org/geoserver/wms?service=WMS&request=GetStyles&version=1.1.1&layers=osm:water_lines_low_zoom

Some background about GeoServer and scale hints is in http://jira.codehaus.org/browse/GEOS-5830.

Related Solutions

GeoServer – Troubleshooting “tiled=true” Not Working for WMS Layers

As noted in the manual you must provide the tilesorigin option with the tiled option or GeoServer doesn't know where to start tiling from (remember each WMS request is stateless). You will also need to have WMS direct integration turned on in GeoWebCache and the following criteria must be met:

When this feature is enabled, GeoServer WMS will cache and retrieve tiles from GeoWebCache (via a GetMap request) only if all of the following criteria are followed:

WMS Direct integration is enabled (you can set this on the Caching defaults page)

tiled=true is included in the request

The request only references a single layer

Caching is enabled for that layer

The image requested is of the same height and width as the size saved in the layer configuration

The requested CRS matches one of the available tile layer gridsets

The image requested lines up with the existing grid bounds

A parameter is included for which there is a corresponding Parameter Filter

To be honest, I can't see a difference in your two images but the most likely problem is that you are requesting WMTS tiles at different resolutions than they are generated at and so OpenLayers is either compressing or expanding them slightly to match.

GeoServer – Not Caching Tiles When Using WMS with Direct Integration

FYI - I found a solution to your problem here in a similar question:

Setting height and width to TileWMS layer in OpenLayers 3

This person (and I had the same result) added to the map options when creating the map:

    pixelRatio: 1,  // this makes the tiles consitent size - makes caching work better

Before I added this to the options, using an OpenLayers layer source of type ol.source.TileWMS was including, in the requests sent to my Geoserver, a FORMAT_OPTIONS setting the dpi value, and the height and width specified were not always 256x256. So the tiles were being dynamically generated as the requests were not matching the cached tiles.

After I added this to the options, all tile requests were consistent with the cached tiles, 256x256 with no FORMAT_OPTIONS in the geoserver requests anymore. So while you've solved the issue by no longer using the WMS / GeoWebCache integration feature of Geoserver, if you ever wish to do so successfully with OpenLayers in the future, this is the solution to your issue.

Best Answer

Related Solutions

GeoServer – Troubleshooting “tiled=true” Not Working for WMS Layers

GeoServer – Not Caching Tiles When Using WMS with Direct Integration

Related Question