Rasters¶

Code¶

1 * {
2   raster-channels: auto;
3   raster-color-map:
4                     color-map-entry(#008000, 70)
5                     color-map-entry(#663333, 256);
6 }

Details¶

There is a single rule which applies a color map to the raster data.

The “raster-channels” attribute activates raster symbolization, the “auto” value is indicates that we are going to use the default choice of bands to symbolize the output (either gray or RBG/RGBA depending on the input data). There is also the possibility of providing a band name or a list of band names in case we want to choose specific bands out of a multiband input, e.g., “1” or “1 3 7”.

The “raster-color-map” attribute builds a smooth gradient between two colors corresponding to two elevation values. Each “color-map-entry” represents one entry or anchor in the gradient:

• The first argument is the color

• The second argument is the value at which we anchor the color

• An optional third argument could specify the opacity of the pixels, as a value between 0 (fully transparent) and 1 (fully opaque). The default, when not specified, is 1, fully opaque.

Line 4 sets the lower value of 70, which is styled a opaque dark green (#008000), and line 5 sets the upper value of 256, which is styled a opaque dark brown (#663333). All data values in between these two quantities will be linearly interpolated: a value of 163 (the midpoint between 70 and 256) will be colored as the midpoint between the two colors (in this case approximately #335717, a muddy green).

Code¶

1 * {
2   raster-channels: auto;
3   raster-opacity: 0.3;
4   raster-color-map: color-map-entry(#008000, 70)
5                     color-map-entry(#663333, 256);
6 }

Details¶

This example is similar to the Two-color gradient example save for the addition of line 3, which sets the opacity of the layer to 0.3 (or 30% opaque). An opacity value of 1 means that the shape is drawn 100% opaque, while an opacity value of 0 means that the shape is rendered as completely transparent. The value of 0.3 means that the raster partially takes on the color and style of whatever is drawn beneath it. Since the background is white in this example, the colors generated from the “raster-color-map” look lighter, but were the raster imposed on a dark background the resulting colors would be darker.

Code¶

1     * {
2       raster-channels: auto;
3       raster-contrast-enhancement: normalize;
4       raster-gamma: 0.5;
5       raster-color-map: color-map-entry(#008000, 70)
6                         color-map-entry(#663333, 256);
7     }

Details¶

This example is similar to the Two-color gradient, save for the addition of the contrast enhancement and gamma attributes on lines 3-4. Line 3 normalizes the output by increasing the contrast to its maximum extent. Line 4 then adjusts the brightness by a factor of 0.5. Since values less than 1 make the output brighter, a value of 0.5 makes the output twice as bright.

Code¶

1     * {
2       raster-channels: auto;
3       raster-color-map:
4                         color-map-entry(black, 150, 0)
5                         color-map-entry(blue, 150)
6                         color-map-entry(yellow, 200)
7                         color-map-entry(red, 250)
8                         color-map-entry(black, 250, 0)
9     }

Details¶

This example creates a three-color gradient, with two extra rules to make ranges of color disappear. The color map behavior is such that any value below the lowest entry gets the same color as that entry, and any value above the last entry gets the same color as the last entry, while everything in between is linearly interpolated (all values must be provided from lower to higher). Line 4 associates value 150 and below with a transparent color (0 opacity, that is, fully transparent), and so does line 8, which makes transparent every value above 250. The lines in the middle create a gradient going from blue, to yellow, to red.

Code¶

1     * {
2       raster-channels: auto;
3       raster-color-map: color-map-entry(#008000, 70)
4                         color-map-entry(#663333, 256, 0);
5     }

Details¶

An alpha channel is another way of referring to variable transparency. Much like how a gradient maps values to colors, each entry in a “raster-color-map” can have a value for opacity (with the default being 1.0 or completely opaque).

In this example, there is a “raster-color-map” with two entries: line 3 specifies the lower bound of 70 be colored dark green (#008000), while line 4 specifies the upper bound of 256 also be colored dark green but with an opacity value of 0. This means that values of 256 will be rendered at 0% opacity (entirely transparent). Just like the gradient color, the opacity is also linearly interpolated such that a value of 163 (the midpoint between 70 and 256) is rendered at 50% opacity.

Code¶

1     * {
2       raster-channels: auto;
3       raster-color-map-type: intervals;
4       raster-color-map: color-map-entry(#008000, 150)
5                         color-map-entry(#663333, 256);
6     }

Details¶

Sometimes color bands in discrete steps are more appropriate than a color gradient. The “raster-color-map-type: intervals” attribute sets the display to output discrete colors instead of a gradient. The values in each entry correspond to the upper bound for the color band such that colors are mapped to values less than the value of one entry but greater than or equal to the next lower entry. For example, line 4 colors all values less than 150 to dark green (#008000) and line 5 colors all values less than 256 but greater than or equal to 150 to dark brown (#663333).

Code¶

 1     * {
 2       raster-channels: auto;
 3       raster-color-map:
 4               color-map-entry(black, 95)
 5               color-map-entry(blue, 110)
 6               color-map-entry(green, 135)
 7               color-map-entry(red, 160)
 8               color-map-entry(purple, 185)
 9               color-map-entry(yellow, 210)
10               color-map-entry(cyan, 235)
11               color-map-entry(white, 256)
12     }

Details¶

This example is similar to the previous ones, and creates a color gradient between 8 colors as reported in the following table