At the Geological Survey of Denmark and Greenland we produce geological maps at various scales, and we want to publish them as WMS-services using ArcGIS 10.1 for Server. While it in some cases makes sense to publish them as separate layers (colored polygons, outlines, faults, dip/strike symbols, place names etc.) we want in this case to control the sequence and visibility of the individual layers at the different scales. This, in combination with the complexity of the cartography, makes use of a (fused) map service cache an obvious choice. Furthermore, we can force the map to get a pixelated appearance when the user zooms in closer than the map can support. This can be a good alternative to simply make the map invisible at higher scales.
It says in the ArcGIS Server documentation: �??WMS services take advantage of a map cache if one is available. The map cache is only used when requesting the original projection, layer order, and layer visibility of the service. The cached tiles are resampled to fit the scale requested by the client, which can take some processing time and reduce the image quality. You'll see the most benefit using a cache if your WMS service has many layers or sophisticated symbology that would otherwise take a long time to draw dynamically. If you have just a few layers and uncomplicated symbology, you may get better performance without a cache.�?�
But it is normal practice to publish the URL of a WMS-service in this form: http://maps.geology.xx/ArcGIS/services/Geological_map/MapServer/WMSServer? i.e. without any LAYERS parameter. This means, that if your WMS-users do not specify all the layers in the correct order in their GETMAP-request, then the Map Server Cache won�??t be used at all!
This leaves us with two aspects of the same basic problem: 1) How can the user get WMS-access to the full geological map with a simple URL? 2) How can we make sure that the Map Server Cache is used?
In ArcMap we use the concept of group layers to turn on the display of a multi-layer map with a single mouse-click. But group layers are not recognized in WMS.
I can think of one solution to the problem, but a very cumbersome one: 1) From ArcMap the full map is exported to a series of image-tiles by a Python-script using DataDrivenPages and ExportToTIFF. 2) A new map service is created on the basis of a MXD with these images as a single image catalog layer.
Do you have any comment or suggestions to this?
Frants von Platen GIS Specialist Geological Survey of Denmark and Greenland www.geus.dk fph@geus.dk
