Indicates the level of translucency as a floating point number whose value is between 0.0 and
1.0 (inclusive). A value of zero means completely transparent. A value of 1.0 means
completely opaque. If null, the default value is 1.0, totally opaque.
The ChannelSelection element specifies the false-color channel selection for a multi-spectral
raster source (such as a multi-band satellite-imagery source). Either a channel may be
selected to display in each of red, green, and blue, or a single channel may be selected to
display in grayscale. (The spelling ?gray? is used since it seems to be more common on the
Web than ?grey? by a ratio of about 3:1.) Contrast enhancement may be applied to each channel
in isolation. Channels are identified by a system and data-dependent character identifier.
Commonly, channels will be labelled as ?1?, ?2?, etc.
the ChannelSelection object set or null if none is available.
The OverlapBehavior element tells a system how to behave when multiple raster images in a
layer overlap each other, for example with satellite-image scenes. LATEST_ON_TOP and
EARLIEST_ON_TOP refer to the time the scene was captured. AVERAGE means to average multiple
scenes together. This can produce blurry results if the source images are not perfectly
aligned in their geo-referencing. RANDOM means to select an image (or piece thereof) randomly
and place it on top. This can produce crisper results than AVERAGE potentially more
efficiently than LATEST_ON_TOP or EARLIEST_ON_TOP. The default behaviour is system-dependent.
The ColorMap element defines either the colors of a palette-type raster source or the mapping
of fixed-numeric pixel values to colors. For example, a DEM raster giving elevations in
meters above sea level can be translated to a colored image with a ColorMap. The quantity
attributes of a color-map are used for translating between numeric matrixes and color rasters
and the ColorMap entries should be in order of increasing numeric quantity so that
intermediate numeric values can be matched to a color (or be interpolated between two
colors). Labels may be used for legends or may be used in the future to match character
values. Not all systems can support opacity in colormaps. The default opacity is 1.0 (fully
opaque). Defaults for quantity and label are system-dependent.
The ContrastEnhancement element defines contrast enhancement for a channel of a false-color
image or for a color image. In the case of a color image, the relative grayscale brightness
of a pixel color is used. ?Normalize? means to stretch the contrast so that the dimmest color
is stretched to black and the brightest color is stretched to white, with all colors in
between stretched out linearly. ?Histogram? means to stretch the contrast based on a
histogram of how many colors are at each brightness level on input, with the goal of
producing equal number of pixels in the image at each brightness level on output. This has
the effect of revealing many subtle ground features. A ?GammaValue? tells how much to
brighten (value greater than 1.0) or dim (value less than 1.0) an image. The default
GammaValue is 1.0 (no change). If none of Normalize, Histogram, or GammaValue are selected in
a ContrastEnhancement, then no enhancement is performed.
The ShadedRelief element selects the application of relief shading (or ?hill shading?) to an
image for a three-dimensional visual effect. It is defined as: Exact parameters of the
shading are system-dependent (for now). If the BrightnessOnly flag is ?0? (false, default),
the shading is applied to the layer being rendered as the current RasterSymbol. If
BrightnessOnly is ?1? (true), the shading is applied to the brightness of the colors in the
rendering canvas generated so far by other layers, with the effect of relief-shading these
other layers. The default for BrightnessOnly is ?0? (false). The ReliefFactor gives the
amount of exaggeration to use for the height of the ?hills.? A value of around 55 (times)
gives reasonable results for Earth-based DEMs. The default value is system-dependent.
The ImageOutline element specifies that individual source rasters in a multi-raster set (such
as a set of satellite-image scenes) should be outlined with either a LineStringSymbol or
An Opacity of 0.0 can be selected for the main raster to avoid rendering the main-raster
pixels, or an opacity can be used for a PolygonSymbolizer Fill to allow the main-raster data
be visible through the fill.