PostGIS Raster : Extending PostgreSQL for The Support of ... - CoDE

For each loaded map
Turn the map on MultiBandSingleBandPseudoColor mode
Set the chosen band as the band to be displayed
Set PseudoColorShader as color shading algorithm for the map
6.3.2 Color Legend
Figure 6.16: Visualisation of band number 2 of a multi band map.
The most important function in color legend construction is computeRasterStats. It computes the
minimum and the maximum pixel values from a set of temporal rasters (or maps). In fact, these values
are resulted from PostgreSQL through a connection. For instance, the minimum pixel value is computed
from the request SELECT min((ST_SummaryStats((rtt).rast)).min) FROM temporalRasterTable
(the temporal raster table is described in the interface Section). The (ST_SummaryStats((rtt).rast)).min)
part gives, for each temporal raster in the temporalRasterTable, a corresponding minimum pixel value.
Hence, the min((ST_SummaryStats((rtt).rast)).min) gives the minimum value of a set of minimum
values according to the definition of the minimum pixel value of a set of temporal rasters.
Each color palette is provided from an external tbl file. The tbl file describes a RGB triple of
color in each row. Hence the number of possible colors of a color palette is the number of lines used
to code colors. Example of a tbl file is something like:
"{ r g b }
102 47 0
153 96 53
..."
Each time, when users choose a color palette from Color legend window, the information related
to this palette, such as the number of colors, the RGB values array and the real data values, is saved
respectively into three variables nColo, arColo and arColV. The creation of a color legend file (a PNG
file) implies the use of these variables, along with the minimum and maximum pixel values of a set of
temporal rasters. For instance, the number of colors decides the color legend length, where each RGB
color is painted as a color ligne. The tick notations are given by variable arColV. The number of tick
notations depends on the number of colors that a palette has. If it has less than 10, the number of tick
notations is equal to the number of available colors. Otherwise, it will be a fixed number and equal
to 10. In this case, the number of colors between two tick notations is the division of the number of
colors by 10.
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