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

2.2.4 Surfaces
Figure 2.6: Multiband raster data [27].
A surface describes a phenomenon that has a value for each point in space. For example, surface
elevation is a continuous area such that every spatial location has a value for ground elevation above
sea level. Other examples include surface rainfall, surface pollution concentration and etc.
The major problem in surface representation is that it is impossible to represent all values for all
locations of a area. Various alternatives exist for representing such surfaces using either features or
rasters. Here are some alternative solutions for surface representation:
Contour Lines
Contour lines: Isolines represent a set of points having an equal value, such as elevation contours.
Contour Bands
Figure 2.7: Surface expressed by contour lines [27].
Contour bands: Each band describes a specified range of values. An area, where each point value
within it belong to a band, will be represented by a corresponding color. Example of such band
consists of all average annual rainfall between 25 cm and 50 cm per year.
Raster Data
Raster data: A matrix of cells where each cell value represents a measure of each point in space.
For example, digital elevation models (DEMs) represented by grids of squares, are frequently used to
describe surface elevation.
Triangulated Irregular Network
A triangulated irregular network (TIN): A data structure represents surfaces as a connected network
of triangles. Each triangle node has x,y coordinates and a surface value z.
The raster and TIN representations can be used to estimate the surface value for any location
using interpolation.
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