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
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 PolygonSymbol.
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