SLD — Styled Layer Descriptor — is an XML-based styling language developed by OGC. It is used to style images offered by OGC Web Map Services (WMS). The WMS SLD profile defines the XML protocol for the application of styling in the context of a WMS. See Using SLD/SE with a WMS for more information.
The SE — Symbology Encoding — standard is the SLD subset that specifically defines the data styling features. There is no coupling between SE and WMS. You can use SE independently, as a generic styling language, also in non-WMS contexts.
Using the SLD and SE standards, you can define uniform styling for geospatial data, and store a comprehensive model for that styling information.
The terms SLD and SE are often used interchangeably. SLD frequently refers to the OGC styling language, although that is actually codified in the SE standard.
SE offers support for common styling requirements for geospatial data.
Vector data, such as points, lines, and polygons
Coverage data, such as elevation data
SE supports various feature styling options, such as:
Icons, such as circles, squares, and crosses
You can also style coverage data, by applying color maps to elevation raster data, for example. See Apply raster color maps for more information.
You can set up and apply predicate rules to assign features to classes, and style each class differently. For an example of rule-based styling, see Apply thematic styling to vector data.
You can also include filters in your styling rules.
You can exclude features from styling. For an example of filtering, see Configuring an SLD on a WFS layer for a demonstration.
In a WMS context, you can request a specific style for a WMS layer. You can formulate such a styling request through an SLD definition. In the SLD, you specify one or more WMS layers, and a styling definition for each of those layers. These can be SE definitions.
You can send your SLD definition to the WMS in two ways:
You embed it in a request to the WMS
You refer to it through a URL in the request. You typically use URLs if a publicly accessible server with pre-defined SLDs is available.
The WMS returns the requested map layer with the requested styling.
You can also use SLD to configure custom data requests, and request a custom data layer from WMS. By means of the SLD UserLayer concept, a client can either embed data or link to data residing on a web service, a WFS feature type for example. With this capability, a WMS can be used as a general rendering engine for user-defined data.
In Luciad products, you can use SLD/SE:
To serve data with custom styling from a WMS
To render custom data through a WMS
To style and filter WFS features
To style data in a standalone application through an SE definition
Although the SLD/SE standard was originally conceived to convey styling information to a WMS, you can also apply SE styling models to data in standalone applications. This means that you can set up SE styling for your data in your LuciadLightspeed or LuciadRIA application without connecting to a WMS server. For more information about SE styling in LuciadLightspeed, see the LuciadLightspeed OGC SLD Styling documentation. For more information about SE styling in LuciadRIA, see LuciadRIA OGC SLD styling.
You can serve custom data layers from a WMS, as well as data rendered with custom styling. The OGC services sample includes a few SLD example requests that demonstrate the possibilities. Run the Luciad OGC Services sample, and see the sample website http://localhost:8080/LuciadOGCServices/#/wms for more information.