To start using the SVS Image server, a client first accesses this URL:
The server responds with an XML file that precisely defines the characteristics of the server, including the available content. The response looks something like this, where, for clarity, line breaks and indentation have been added and some content (denoted by ...) has been omitted:
<?xml version="1.0" encoding="UTF-8" ?> <WMS_Capabilities version="1.3.0" ...> ... <Capability> <Request> <GetCapabilities>...</GetCapabilities> <GetMap><Format>image/png</Format>...</GetMap> </Request> <Exception><Format>XML</Format></Exception> <Layer> ... <Layer opaque="0" noSubsets="1" fixedWidth="1024" fixedHeight="1024"> <Name>2890_17402</Name> <Title>African Fires during 2002 (1024x1024 Animation)</Title> <Abstract>...</Abstract> <KeywordList>...</KeywordList> <CRS>CRS:84</CRS> <EX_GeographicBoundingBox>...</EX_GeographicBoundingBox> <BoundingBox CRS="CRS:84" minx="-22" miny="-39" maxx="58" maxy="41"/> <Dimension name="time" units="ISO8601" default="2002-12-31"> 2002-01-01/2002-12-31/P1D </Dimension> <Attribution>...</Attribution> <MetadataURL type="FGDC:1998">...</MetadataURL> <DataURL>...</DataURL> <Style><Name>composite</Name>...</Style> <Style><Name>overlay</Name>...</Style> </Layer> ... </Layer> </Capability> </WMS_Capabilities>
The most critical part of this "Capabilities XML" is the set of nested Layers it defines. If a Layer contains a <Name> element, it is a "Named Layer", and a geographically referenced image or "map" of that layer can be requested. If a Layer is not named, then the Layer is simply part of an organizing scheme for the content of the server and cannot be requested by itself.
Once a client receives this response, it may indicate any or all Named Layers in the Capabilities XML to the user as available maps. A client should use the <Title> element of the Layer in any human-readable list, with the <Abstract> element as a supplemental, more complete description of the Layer.
Important note: By definition, WMS queries and responses must adhere to a specific version of the WMS specification. The examples in this documentation assume WMS version 1.3.0, which is documented here. The SVS Image Server also supports WMS version 1.1.1. Documentation on version 1.1.1 is available here. Both documents describe the process for negotiating an acceptable version between the client and the server.
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