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@XmlSchema(URL="http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd", specification=OGC_02070)

## Package org.opengis.sld

Allows user-defined symbolization of feature data.

See:
Description

Interface Summary
ExternalGraphic | Points to an external file that contains an image of some kind, such as a CGM, JPG, or SVG.
ExternalGraphicOrMark | Common subclass for the two types of markers that can appear as children of a `Graphic` object, namely `Mark` and `ExternalGraphic`.
FeatureStyle | Represents a style that applies to the features of a given type.
FeatureStyleFactory | Class that knows how to parse `FeatureStyle` elements from various places.
Fill | Indicates how the interior of polygons will be filled.
Font | Identifies a font of a certain family, style, and size.
Graphic | Not to be confused with GO-1's Graphic, this represents a little picture, such as a GIF or JPG, that can be used in rendering.
Halo | Describes the settings of a "halo" effect as it is applied to text.
LinePlacement | Helds by a `TextSymbol` to indicate that text should be drawn at some distance from a line.
LineSymbol | Gives directions for how to draw lines on a map.
Mark | Indicate that one of a few predefined shapes will be drawn at the points of the geometry.
PointPlacement | Used in the `TextSymbol` class to indicate that text should be drawn starting at a particular point and extending in a straight line.
PointSymbol | Indicates how to draw point geometries on a map.
PolygonSymbol | Holds the information that indicates how to draw the lines and the interior of polygons.
Rule | A rule consists of two important parts: a filter and a list of symbols.
Stroke | Contains all the information needed to draw styled lines.
StyleVisitor | Interface that can be implemented by objects that want to perform some action on style objects.
Symbol | Abstract superclass of the various symbol classes.
SymbolVisitor | Visitor with `visit` methods to be called by `Symbol.accept(...)`.
TextPlacement | Abstract base class for the two different classes that specify the placement of text in a style, namely `PointPlacement` and `LinePlacement`.
TextSymbol | Indicates how text will be drawn.

## Package org.opengis.sld Description

Allows user-defined symbolization of feature data. The following is adapted from OpenGIS® Styled Layer Descriptor specification.

Package `org.opengis.layer` describes the appearance of a map in terms of styled layers. A styled layer can be considered as a transparent sheet with features symbolized upon it. A map is made up of a number of these styled layers put together in a specified order. The styled layers are said to be Z-ordered. Users can define more complex or simpler maps by adding or removing styled layers.

A styled layer itself represents a particular combination of layer and a style in which that layer can be symbolized. Conceptually, the layer defines a stream of features and the style defines how those features are symbolized. This concept is underlined by the fact that there may be multiple styles in which a layer can be symbolized.

### Scale selection

The `MinScaleDenominator` and `MaxScaleDenominator` elements of a `Rule` define the range of map-rendering scales for which the rule should be applied. The values used are actually the scale denominators relative to a "standardized rendering pixel size".

The "standardized rendering pixel size" is defined to be 0.28mm × 0.28mm (millimeters). Frequently, the true pixel size of the final rendering device is unknown in the web environment, and 0.28mm is a common actual size for contemporary video displays. If the map-rendering software has information available about the actual pixel size of the final display device, then an extra processing step will be needed (if the actual pixel size is different from the standard pixel size) to adjust the actual rendering scale to calculate the standard rendering scale, which will then be used to compare to the scale range of an SLD rule. If the actual display device has non-square pixels, then a method of "linear equivalence" to square pixels should be used to calculate the standard rendering scale.

Since it is common to integrate the output of multiple servers into a single displayed result in the web-mapping environment, it is important that different map servers have consistent behaviour with respect to processing scales, so that all of the independent servers will select or deselect rules at the same scales.

To insure consistent behaviour, scales relative to coordinate spaces must be handled consistently between map servers. For geographic coordinate systems, which use angular units, the angular coverage of a map should be converted to linear units for computation of scale by using the circumference of the Earth at the equator and by assuming perfectly square linear units. For linear coordinate systems, the size of the coordinate space should be used directly without compensating for distortions in it with respect to the shape of the real Earth.

### Feature filtering

The `Filter` and `ElseFilter` elements of a `Rule` allow the selection of features in rules to be controlled by attribute conditions. As discussed in the previous section, rule activation may also be controlled by the `MinScaleDenominator` and the `MaxScaleDenominator` elements as well as the map-rendering scale.

### Symbolizers

Embedded inside of `Rule`s, which group conditions for styling features, are symbolizers. A symbolizer describes how a feature is to appear on a map. The symbolizer describes not just the shape that should appear but also such graphical properties as color and opacity. A symbol is obtained by specifying one of a small number of different types of symbolizer and then supplying parameters to override its default behaviour. Currently, four types of symbolizers are defined:

- Line
- Polygon
- Point
- Text

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