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package org.geotools.styling
Allows for symbolization of geospatial data.
For many of us in geotools *this* is the reason we came along for the ride -
a pretty picture. The contents of this package are adapted from the
OpenGIS® Styled Layer Descriptor
specification v1.0.0.
Conformance to SLD 1.0.0
We may experiment with our own (or SLD 1.1) ideas but will mark such
experiments for you. This is only an issue of you are considering writing out
these objects for interoptability with other systems.
General stratagy for supporting multiple SLD versions (and experiments):
- These interfaces will reflect the current published specification
- Our implementations will be BIGGER and more capabile then any
one specification
- We cannot defined explicit interfaces tracking each version until we
move to Java 5 (perferably GeoAPI would hold these anyways)
- We can provided javadocs indicating extentions, and isolate these using
the normal java convention: TextSymbolizer and TextSymbolizer2 (In short you
will have to go out of your way to work with a hack or experiment, you won't
depend on one by accident)
- We can use Factories (aka SLD1Factory and SLD1_1Factory and SEFactory)
to support the creation of conformant datastructures. Code (such as user
interfaces) can be parameratized with these factories when they need to
confirm to an exact version supported by an individual service. We hope that
specifications are always adative, and will be forced to throw unsupported
exceptions when functionality is removed from a specification.
Care and Feeding of Style Objects
SLD is an XML specification, the definition of objects capturing this information,
the binding of objects to these XML documents, and the provision of events
on object modification all need to be accounted for.
StyleFactory
As with all geotools work construction of styling constructs is handled by a
Factory(GOF). Quickly a Factory is used when working with interfaces,
anything that would of been a constructor is set up as an create method.
StyleFactory factory = StyleFactoryFinder.createStyleFactory();
StyleLayerDescriptor sld = factory.createStyleLayerDescriptor();
// an empty sld document
sld.setTitle("Basic Black");
sld.setAbstract("Grayscale style suitable for use with photocopiers");
When creating a complex data structure direct use of a Factory is a pain.
Which leads us to the next section.
Notes:
- At this time one implementation of StyleFactory is available, this will
not provide true in the future (as SLD experiments, and code generation
are brought to bare on future specifications).
StyleBuilder
When constructing a complex data structure, such as an SLD document, the use
of a Factory is a bit of a pain. That is where StyleBuilder is brought
to bare. A Builder is simply a class that help you construct a complicated
data structure, for a make involved/interesting example of a builder have a look
at the graph package.
Example
The following code example has been borrowed from the geotools website,
for additional examples (and advice) please consult the user documentation.
private Style buildStyle() throws Exception {
StyleBuilder sb = new StyleBuilder();
FilterFactory ff = sb.getFilterFactory();
Style style = sb.createStyle();
style.setName("MyStyle");
// "testPoint" feature type style
Mark testMark = sb.createMark(sb.attributeExpression("name"),
sb.createFill(Color.RED, 0.5), null);
Graphic graph = sb.createGraphic(null, new Mark[] { testMark }, null,
sb.literalExpression(1), sb.attributeExpression("size"),
sb.attributeExpression("rotation"));
style.addFeatureTypeStyle(sb.createFeatureTypeStyle("testPoint",
new Symbolizer[] { sb.createPointSymbolizer(graph) }));
// "labelPoint" feature type style
AnchorPoint anchorPoint = sb.createAnchorPoint(sb.attributeExpression("X"),
sb.attributeExpression("Y"));
PointPlacement pointPlacement = sb.createPointPlacement(anchorPoint, null,
sb.literalExpression(0));
TextSymbolizer textSymbolizer = sb.createTextSymbolizer(sb.createFill(Color.BLACK),
new Font[] { sb.createFont("Lucida Sans", 10), sb.createFont("Arial", 10) },
sb.createHalo(), sb.attributeExpression("name"), pointPlacement, null);
Mark circle = sb.createMark(StyleBuilder.MARK_CIRCLE, Color.RED);
Graphic graph2 = sb.createGraphic(null, circle, null, 1, 4, 0);
PointSymbolizer pointSymbolizer = sb.createPointSymbolizer(graph2);
style.addFeatureTypeStyle(sb.createFeatureTypeStyle("labelPoint",
new Symbolizer[] { textSymbolizer, pointSymbolizer }));
return style;
}
References
The following links will be of interest:
- SLD 1.0.0
- Design Patterns, GOF
@author Ian Turton, CCG
@author James Macgill, CCG
@author Jody Garnett, Refractions Research
@since GeoTools 2.0
@version SLD 1.0