Raster Meets Point Data - Open Source Geospatial Tools: Applications in Earth Observation - page 157

color entry for each possible pixel value in the image). Missing color values will
either be interpolated by the algorithm (default) or matched to the nearest color entry
(option -nearest_color_entry ). The interpolation can be avoided with the
option exact_color_entry . In that case, the elevation must exactly match the
provided color table or a no-data (black) value will be used.

color_text_file
Text-based color configuration file.
-alpha
Add an alpha channel to the output raster.
-exact_color_entry
Use strict matching when searching in the color configuration file. If none match-
ing color entry is found, the “0,0,0,0” RGBA quadruplet will be used.
-nearest_color_entry
Use the RGBA quadruplet corresponding to the closest entry in the color config-
uration file.

An example of how to use gdaldem color-relief to create an RGB color
image from a slope image produced by gdaldem is given in Sect. 10.6.2 .

10.6.5 Terrain Ruggedness Index

TRI is an analysis mode that calculates the terrain ruggedness index (TRI). It is
defined as the average of the absolute difference between a central pixel and its 3

3
neighboring pixels. The output data type is Float32 and the no-data value is fixed to
−

×

9999.

10.6.6 Topographic Position Index

TPI is an analysis mode that calculates the topographic position index (TPI). It is
defined as the difference between the central pixel and the average of its 3 3

neighboring pixels. The output data type is Float32. The no-data value is fixed to
−

×

9999.

10.6.7 Roughness

Roughness is an analysis mode that calculates the roughness of the DEM. This is
the range (difference) between the maximum and minimum value within a 3 × 3

window. The output data type is Float32. The no-data value is fixed to − 9999.