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Raster terrain analysis

Aspect

Calculates the aspect of the Digital Terrain Model in input. The final aspect raster layer contains values from 0 to 360 that express the slope direction: starting from North (0°) and continuing clockwise.

../../../../_images/aspect.png

Aspect values

The following picture shows the aspect layer reclassified with a color ramp:

../../../../_images/aspect_2.png

Aspect layer reclassified

Parameters

Elevation layer [raster]
Digital Terrain Model raster layer.
Z factor [number]

Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y ones, for example miles and meters. You can use this parameter to adjust the final result.

Default: 1.0

Outputs

Aspect [raster]
Aspect raster layer.

Hillshade

Calculates the hillshade raster layer given a Digital Terrain Model in input.

The shading of the layer is calculated according to the sun position: you have the options to change both the horizontal angle (azimuth) and the vertical angle (sun elevation) of the sun.

../../../../_images/azimuth.png

Azimuth and vertical angle

The hillshade layer contains values from 0 (complete shadow) to 255 (complete sun). Hillshade is used usually to better understand the relief of the area.

../../../../_images/hillshade.png

Hillshade layer with azimuth 300 and vertical angle 45

Particularly interesting is to give the hillshade layer a transparency value and overlap it with the elevation raster:

../../../../_images/hillshade_2.png

Overlapping the hillshade with the elevation layer

Parameters

Elevation layer [raster]
Digital Terrain Model raster layer.
Z factor [number]

You can use this parameter to exaggerate the final result in order to give it a stronger output.

Default: 1.0

Azimuth (horizontal angle) [number]

Set the horizontal angle (in degrees) of the sun. The range of these values can go from 0 (North) continuing clockwise.

Default: 300

Vertical angle [number]

Set the vertical angle (in degrees) of the sun, that is the height of the sun. Values can go from 0 (minimum elevation) to 90 (maximum elevation).

Default: 40

Outputs

Hillshade [raster]
Hillshade raster layer.

Hypsometric curves

Calculates hypsometric curves for an input Digital Elevation Model. Curves are produced as csv file in an output folder specified by the user.

Hypsometric curves are a histogram of the cumulative distribution of elevation values in a geographical area. You can use hypsometric curves to detect differences in the landscape due to the geomorphology of the territory.

Parameters

DEM to analyze [raster]
Digital Terrain Model raster layer to use for calculating altitudes.
Boundary layer
Polygonal vector layer with boundaries of areas used to calculate hypsometric curves.
Step

Distance between curves.

Default: 100.0

Use % of area instead of absolute value [boolean]

Write area percentage to “Area” field of the CSV file instead of absolute area value.

Default: False

Outputs

Hypsometric curves [folder]

Directory where output will be saved. For each feature from input vector layer CSV file with area and altitude values will be created.

File name consists of prefix hystogram_ followed by layer name and feature ID.

../../../../_images/hypsometric.png

Relief

Creates a shaded relief layer from digital elevation data. You can specify manually all the relief color or you can let the algorithm choose automatically all the relief classes.

../../../../_images/relief.png

Relief layer

Parameters

Elevation layer [raster]
Digital Terrain Model raster layer.
Z factor [number]

You can use this parameter to exaggerate the final result in order to give it a stronger output.

Default: 1.0

Generate relief classes automatically [boolean]

If you check this option the algorithm will create all the relief color classes automatically.

Default: False

Relief colors [table widget]

Optional

Use the following table widget if you want to choose the relief colors manually. You can add as many color classes as you want: for each class you can choose the lower and upper bound and finally by clicking on the color row you can choose the color thanks to the color widget.

../../../../_images/relief_table.png

Manually relief color classes

All the buttons of the right side panel give you the chance to: add or remove color classes, change the order of the color classes already defined, open an existing file with color classes and save the current classes as file.

Outputs

Relief [raster]
Relief raster layer.

Ruggedness index

Calculates the quantitative measurement of terrain heterogeneity described by Riley et al. (1999). It is calculated for every location, by summarizing the change in elevation within the 3x3 pixel grid.

Each pixel contains the difference in elevation from a center cell and the 8 cells surrounding it.

../../../../_images/ruggedness.png

Ruggedness layer from low (red) to high values (green)

Parameters

Elevation layer [raster]
Digital Terrain Model raster layer.
Z factor [number]

You can use this parameter to exaggerate the final result in order to give it a stronger output.

Default: 1.0

Outputs

Ruggedness [raster]
Ruggedness raster layer.

Slope

Calculates the slope from an input raster layer. The slope is the angle of inclination of the terrain and is expressed in degrees.

In the following picture you can see to the left the DTM layer with the elevation of the terrain while to the right the calculated slope:

../../../../_images/slope2.png

Flat areas in red, steep areas in blue

Parameters

Elevation raster [raster]
Digital Terrain Model raster layer.
Z factor [number]

You can use this parameter to exaggerate the final result in order to give it a stronger output.

Default: 1.0

Outputs

Slope [raster]
Slope raster layer.