24.1.20. Raster terrain analysis

24.1.20.1. 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.

Fig. 24.72 Aspect values

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

Fig. 24.73 Aspect layer reclassified

Parameters

Basic parameters

Label	Name	Type	Description
Elevation layer	INPUT	[raster]	Digital Terrain Model raster layer
Z factor	Z_FACTOR	[numeric: double] Default: 1.0	Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. The default is 1 (no exaggeration).
Aspect	OUTPUT	[raster] Default: [Save to temporary file]	Specify the output aspect raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value Added in 4.0	NODATA	[numeric: double] Default: -9999.0	Value to use for NoData cells in the output layer.
Creation options Optional Added in 4.0	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Aspect	OUTPUT	[raster]	The output aspect raster layer

Python code

Algorithm ID: native:aspect

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.2. Channel network and drainage basins from DEM

Added in 4.4

Extracts vector channel network lines, drainage basin polygons, and topological junction node points directly from an elevation raster (DEM).

The analysis executes a 3-step pipeline:

1. D8 Flow Routing: Computes single-direction steepest descent flow directions

2. Strahler Stream Ordering: Calculates topological stream orders

3. Vector Network Extraction: Traces vector channels, delineates catchments, and identifies key topological junction nodes.

The output Junctions layer contains topological nodes from the channel network. These are classified according to type:

• Spring: Channel headwater initiation point matching the stream order threshold.

• Junction: Tributary confluence point where two or more stream channels meet.

• Outlet: Terminal discharge node exiting the raster boundary or draining into a terrain sink.

• Mouth: Confluence pour point entering a higher-order stream segment (delineated when subbasins are enabled).

See also

This algorithm is a port of SAGA’s Channel Network and Drainage Basins tool.

Parameters

Label	Name	Type	Description
Elevation raster	INPUT	[raster]	Digital Terrain Model raster layer
Minimum stream order threshold	THRESHOLD	[numeric: integer] Default: 5	Strahler order to begin a channel. Minimum: 1
Delineate subbasins	SUBBASINS	[boolean] Default: True
Channels Optional	CHANNELS	[vector: line] Default: [Save to temporary file]	Specify the output line vector layer representing the extracted channels. One of: Skip Output Save to a Temporary File Save to File…
Drainage Basins Optional	BASINS	[vector: polygon] Default: [Save to temporary file]	Specify the output polygon vector layer representing the extracted drainage basins. One of: Skip Output Save to a Temporary File Save to File…
Junctions Optional	JUNCTIONS	[vector: point] Default: [Save to temporary file]	Specify the output point vector layer representing the extracted junctions. One of: Skip Output Save to a Temporary File Save to File…

Outputs

Label	Name	Type	Description
Channels	CHANNELS	[vector: line]	The output line vector layer representing the channel network with the following fields: SEGMENT_ID: ID of the channel segment NODE_A: Upstream node of the segment NODE_B: Downstream node of the segment BASIN: Basin ID ORDER: Strahler order ORDER_CELL: Strahler order of the original raster layer LENGTH: Length of the segment
Drainage Basins	BASINS	[vector: polygon]	The output polygon vector layer representing the drainage basins with the following attributes: VALUE: Basin ID AREA: Basin area PERIMETER: Basin perimeter ORDER: Basin Strahler order
Junctions	JUNCTIONS	[vector: point]	The output point vector layer representing topological nodes from the channel network, with the following attributes: ID: Junction ID TYPE: Junction type ORDER: Junction Strahler order BASIN: Basin ID These junctions are classified according to their TYPE value.

Python code

Algorithm ID: native:channelnetworkfromdem

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.3. Channel network and drainage basins from multiple inputs

Added in 4.4

Extracts vector channel network lines, drainage basin polygons, and topological junction node points using pre-computed elevation (DEM), D8 flow direction, and Strahler stream order rasters.

This algorithm bypasses internal raster flow routing and stream order generation, making it ideal when flow direction and Strahler order rasters have already been computed in prior processing steps.

The output Junctions layer contains topological nodes from the channel network. These are classified according to type:

• Spring: Channel headwater initiation point matching the stream order threshold.

• Junction: Tributary confluence point where two or more stream channels meet.

• Outlet: Terminal discharge node exiting the raster boundary or draining into a terrain sink.

• Mouth: Confluence pour point entering a higher-order stream segment (delineated when subbasins are enabled).

See also

This algorithm is a port of SAGA’s Channel Network and Drainage Basins tool.

Parameters

Label	Name	Type	Description
Elevation raster	INPUT_DEM	[raster]	Digital Terrain Model raster layer
Flow direction raster	INPUT_FLOW_DIR	[raster]
Strahler order raster	INPUT_STRAHLER	[raster]
Minimum stream order threshold	THRESHOLD	[numeric: integer] Default: 5	Strahler order to begin a channel. Minimum: 1
Delineate subbasins	SUBBASINS	[boolean] Default: True
Channels Optional	CHANNELS	[vector: line] Default: [Save to temporary file]	Specify the output line vector layer representing the extracted channels. One of: Skip Output Save to a Temporary File Save to File…
Drainage Basins Optional	BASINS	[vector: polygon] Default: [Save to temporary file]	Specify the output polygon vector layer representing the extracted drainage basins. One of: Skip Output Save to a Temporary File Save to File…
Junctions Optional	JUNCTIONS	[vector: point] Default: [Save to temporary file]	Specify the output point vector layer representing the extracted junctions. One of: Skip Output Save to a Temporary File Save to File…

Outputs

Label	Name	Type	Description
Channels	CHANNELS	[vector: line]	The output line vector layer representing the channel network with the following fields: SEGMENT_ID: ID of the channel segment NODE_A: Upstream node of the segment NODE_B: Downstream node of the segment BASIN: Basin ID ORDER: Strahler order ORDER_CELL: Strahler order of the original raster layer LENGTH: Length of the segment
Drainage Basins	BASINS	[vector: polygon]	The output polygon vector layer representing the drainage basins with the following attributes: VALUE: Basin ID AREA: Basin area PERIMETER: Basin perimeter ORDER: Basin Strahler order
Junctions	JUNCTIONS	[vector: point]	The output point vector layer representing topological nodes from the channel network, with the following attributes: ID: Junction ID TYPE: Junction type ORDER: Junction Strahler order BASIN: Basin ID These junctions are classified according to their TYPE value.

Python code

Algorithm ID: native:channelnetworkfromflowdirandorder

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.4. DTM filter (slope-based)

Added in 3.34

Can be used to filter a digital elevation model in order to classify its cells into ground and object (non-ground) cells.

The tool uses concepts as described by Vosselman (2000) and is based on the assumption that a large height difference between two nearby cells is unlikely to be caused by a steep slope in the terrain. The probability that the higher cell might be non-ground increases when the distance between the two cells decreases. Therefore the filter defines a maximum height difference (dz_max) between two cells as a function of the distance (d) between the cells (dz_max( d ) = d). A cell is classified as terrain if there is no cell within the kernel radius to which the height difference is larger than the allowed maximum height difference at the distance between these two cells.

The approximate terrain slope (s) parameter is used to modify the filter function to match the overall slope in the study area (dz_max( d ) = d * s). A 5 % confidence interval (ci = 1.65 * sqrt( 2 * stddev )) may be used to modify the filter function even further by either relaxing (dz_max( d ) = d * s + ci) or amplifying (dz_max( d ) = d * s - ci) the filter criterium.

References: Vosselman, G. (2000): Slope based filtering of laser altimetry data. IAPRS, Vol. XXXIII, Part B3, Amsterdam, The Netherlands, 935-942

See also

This algorithm is a port of the SAGA DTM Filter (slope-based) tool.

Parameters

Basic parameters

Label	Name	Type	Description
Input layer	INPUT	[raster]	Digital Terrain Model raster layer
Band number	BAND	[raster band]	The band of the DEM to consider
Kernel radius (pixels)	RADIUS	[numeric: integer] Default: 5	The radius of the filter kernel (in pixels). Must be large enough to reach ground cells next to non-ground objects.
Terrain slope (%, pixel size/vertical units)	TERRAIN_SLOPE	[numeric: double] Default: 30.0	The approximate terrain slope in %. The terrain slope must be adjusted to account for the ratio of height units vs raster pixel dimensions. Used to relax the filter criterium in steeper terrain.
Filter modification	FILTER_MODIFICATION	[list] Default: 0	Choose whether to apply the filter kernel without modification or to use a confidence interval to relax or amplify the height criterium. 0 - None 1 - Relax filter 2 - Amplify
Standard deviation	STANDARD_DEVIATION	[numeric: double] Default: 0.1	The standard deviation used to calculate a 5% confidence interval applied to the height threshold.
Output layer (ground) Optional	OUTPUT_GROUND	[raster] Default: [Save to temporary file]	Specify the filtered DEM containing only cells classified as ground. One of: Skip Output Save to a Temporary File Save to File…
Output layer (non-ground objects) Optional	OUTPUT_NONGROUND	[raster] Default: [Skip output]	Specify the non-ground objects removed by the filter. One of: Skip Output Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Creation options Optional Added in 3.40	CREATION_OPTIONS (for QGIS <= 3.42, this was CREATE_OPTIONS)	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Output layer (ground)	OUTPUT_GROUND	[raster]	The filtered DEM containing only cells classified as ground.
Output layer (non-ground objects)	OUTPUT_NONGROUND	[raster]	The non-ground objects removed by the filter.

Python code

Algorithm ID: native:dtmslopebasedfilter

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.5. Fill sinks (Wang & Liu)

Added in 3.44

Uses a method proposed by Wang & Liu to identify and fill surface depressions in digital elevation models.

The method was enhanced to allow the creation of hydrologically sound elevation models, i.e. not only to fill the depression(s) but also to preserve a downward slope along the flow path. If desired, this is accomplished by preserving a minimum slope gradient (and thus elevation difference) between cells.

References: Wang, L. & H. Liu (2006): An efficient method for identifying and filling surface depressions in digital elevation models for hydrologic analysis and modelling. International Journal of Geographical Information Science, Vol. 20, No. 2: 193-213.

See also

This algorithm is a port of the SAGA Fill Sinks (Wang & Liu) tool.

Parameters

Basic parameters

Label	Name	Type	Description
Input layer	INPUT	[raster]	Digital Terrain Model raster layer
Band number	BAND	[raster band] Default: 1	The band of the DEM to consider
Minimum slope (degrees)	MIN_SLOPE	[numeric: double] Default: 0.01	Minimum slope gradient to preserve from cell to cell; with a value of zero, sinks are filled up to the spill elevation (which results in flat areas).
Output layer (filled DEM) Optional	OUTPUT_FILLED_DEM	[raster] Default: [Save to temporary file]	Specify the output raster corresponding to the depression-free DEM. One of: Skip Output Save to a Temporary File Save to File…
Output layer (flow directions) Optional	OUTPUT_FLOW_DIRECTIONS	[raster] Default: [Skip output]	Specify the output raster with computed flow directions. One of: Skip Output Save to a Temporary File Save to File…
Output layer (watershed basins) Optional	OUTPUT_WATERSHED_BASINS	[raster] Default: [Skip output]	Specify the output raster corresponding to the delineated watershed basins. One of: Skip Output Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Creation options Optional	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Output layer (filled DEM)	OUTPUT_FILLED_DEM	[raster]	Output raster corresponding to the depression-free digital elevation model.
Output layer (flow directions)	OUTPUT_FLOW_DIRECTIONS	[raster]	Output raster with computed flow directions; 0=N, 1=NE, 2=E, … 7=NW.
Output layer (watershed basins)	OUTPUT_WATERSHED_BASINS	[raster]	Output raster corresponding to the delineated watershed basins.

Python code

Algorithm ID: native:fillsinkswangliu

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.6. Flow connectivity

Added in 4.4

Calculates deterministic 8 (D8) flow connectivity for each cell in an input elevation raster (DEM).

Output cell values represent the number of immediate 8-neighbor adjacent cells (0 to 8) whose D8 steepest downslope flow direction points directly into the cell:

• 0 = Ridge, crest, or spring cell receiving no incoming surface flow.

• 1 = Channel segment cell receiving flow from a single upstream neighbor.

• 2+ = Stream junction or confluence cell receiving flow from multiple converging upstream paths.

See also

This algorithm is a port of the flow connectivity calculation from SAGA Channel Network and Drainage Basins tool.

Parameters

Basic parameters

Label	Name	Type	Description
Input layer	INPUT	[raster]	Digital Terrain Model raster layer
Flow connectivity	OUTPUT	[raster] Default: Save to temporary file	Specify the output flow connectivity raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value	NODATA	[numeric: integer] Default: -9999	Value to use for NoData cells in the output layer.
Creation options Optional	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Flow connectivity	OUTPUT	[raster]	The output flow connectivity raster layer.

Python code

Algorithm ID: native:flowconnectivity

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.7. Flow direction

Added in 4.4

Calculates deterministic 8 (D8) flow directions for each cell in an input elevation raster (DEM).

Flow direction values are output as 8-neighbor directional indices numbered clockwise starting from North: 0 = North, 1 = North-East, 2 = East, 3 = South-East, 4 = South, 5 = South-West, 6 = West, 7 = North-West. Sink/pit cells are assigned a value of -1 in the output, and flat areas are assigned -2. Cells with no downslope neighbor or NoData elevation values are assigned nodata in the output.

See also

This algorithm is a port of the flow direction calculation from SAGA Channel Network and Drainage Basins tool.

Parameters

Basic parameters

Label	Name	Type	Description
Input layer	INPUT	[raster]	Digital Terrain Model raster layer
Flow direction	OUTPUT	[raster] Default: Save to temporary file	Specify the output flow direction raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value	NODATA	[numeric: integer] Default: -9999	Value to use for NoData cells in the output layer.
Creation options Optional	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Flow direction	OUTPUT	[raster]	The output flow direction raster layer.

Python code

Algorithm ID: native:flowdirection

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.8. Hillshade

Calculates the hillshade raster layer given an input Digital Terrain Model.

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.

Fig. 24.74 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.

Fig. 24.75 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:

Fig. 24.76 Overlapping the hillshade with the elevation layer

Parameters

Basic parameters

Label	Name	Type	Description
Elevation layer	INPUT	[raster]	Digital Terrain Model raster layer
Z factor	Z_FACTOR	[numeric: double] Default: 1.0	Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. Increasing the value of this parameter will exaggerate the final result (making it look more “hilly”). The default is 1 (no exaggeration).
Azimuth (horizontal angle)	AZIMUTH	[numeric: double] Default: 300.0	Set the horizontal angle (in degrees) of the sun (clockwise direction). Range: 0 to 360. 0 is north.
Vertical angle	V_ANGLE	[numeric: double] Default: 40.0	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).
Hillshade	OUTPUT	[raster] Default: Save to temporary file	Specify the output hillshade raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value Added in 4.0	NODATA	[numeric: double] Default: -9999.0	Value to use for NoData cells in the output layer.
Creation options Optional Added in 4.0	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Hillshade	OUTPUT	[raster]	The output hillshade raster layer

Python code

Algorithm ID: native:hillshade

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.9. Hypsometric curves

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

A hypsometric curve is a cumulative histogram 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

Label	Name	Type	Description
DEM to analyze	INPUT_DEM	[raster]	Digital Terrain Model raster layer to use for calculating altitudes
Boundary layer	BOUNDARY_LAYER	[vector: polygon]	Polygon vector layer with boundaries of areas used to calculate hypsometric curves
Step	STEP	[numeric: double] Default: 100.0	Vertical distance between curves
Use % of area instead of absolute value	USE_PERCENTAGE	[boolean] Default: False	Write area percentage to “Area” field of the CSV file instead of the absolute area
Hypsometric curves	OUTPUT_DIRECTORY	[folder]	Specify the output folder for the hypsometric curves. One of: Save to a Temporary Directory Save to Directory

Outputs

Label	Name	Type	Description
Hypsometric curves	OUTPUT_DIRECTORY	[folder]	Directory containing the files with the hypsometric curves. For each feature from the input vector layer, a CSV file with area and altitude values will be created. The file names start with histogram_, followed by layer name and feature ID.

Python code

Algorithm ID: qgis:hypsometriccurves

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.10. Relief

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

Fig. 24.77 Relief layer

Parameters

Basic parameters

Label	Name	Type	Description
Elevation layer	INPUT	[raster]	Digital Terrain Model raster layer
Z factor	Z_FACTOR	[numeric: double] Default: 1.0	Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. Increasing the value of this parameter will exaggerate the final result (making it look more “hilly”). The default is 1 (no exaggeration).
Generate relief classes automatically	AUTO_COLORS	[boolean] Default: False	If you check this option the algorithm will create all the relief color classes automatically
Relief colors Optional	COLORS	[table widget]	Use the 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. Fig. 24.78 Manually setting of relief color classes The buttons in 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.
Relief	OUTPUT	[raster] Default: [Save to temporary file]	Specify the output relief raster layer. One of: Save to a Temporary File Save to File…
Frequency distribution Optional	FREQUENCY_DISTRIBUTION	[vector: table] Default: [Skip output]	Specify the CSV table for the output frequency distribution. One of: Skip Output Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value Added in 4.4	NODATA	[numeric: double] Default: -9999.0	Value to use for NoData cells in the output layer.
Creation options Optional Added in 4.4	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Relief	OUTPUT	[raster]	The output relief raster layer
Frequency distribution	OUTPUT	[vector: table]	The output frequency distribution

Python code

Algorithm ID: native:relief

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.11. 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.

Fig. 24.79 Ruggedness layer from low (red) to high values (green)

Parameters

Basic parameters

Label	Name	Type	Description
Elevation layer	INPUT	[raster]	Digital Terrain Model raster layer
Z factor	Z_FACTOR	[numeric: double] Default: 1.0	Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. Increasing the value of this parameter will exaggerate the final result (making it look more rugged). The default is 1 (no exaggeration).
Ruggedness	OUTPUT	[raster] Default: [Save to temporary file]	Specify the output ruggedness raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value Added in 4.0	NODATA	[numeric: double] Default: -9999.0	Value to use for NoData cells in the output layer.
Creation options Optional Added in 4.0	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Ruggedness	OUTPUT	[raster]	The output ruggedness raster layer

Python code

Algorithm ID: native:ruggednessindex

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.12. Slope

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

Fig. 24.80 Flat areas in red, steep areas in blue

Parameters

Basic parameters

Label	Name	Type	Description
Elevation layer	INPUT	[raster]	Digital Terrain Model raster layer
Z factor	Z_FACTOR	[numeric: double] Default: 1.0	Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. Increasing the value of this parameter will exaggerate the final result (making it steeper). The default is 1 (no exaggeration).
Slope	OUTPUT	[raster] Default: [Save to temporary file]	Specify the output slope raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value Added in 4.0	NODATA	[numeric: double] Default: -9999.0	Value to use for NoData cells in the output layer.
Creation options Optional Added in 4.0	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Slope	OUTPUT	[raster]	The output slope raster layer

Python code

Algorithm ID: native:slope

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.13. Strahler order from DEM

Added in 4.4

Calculates Strahler stream order from an input elevation raster (DEM).

D8 flow directions are computed internally to traverse channel trees topographically. Confluences of two stream channels of order N produce a downstream channel of order N + 1. When the threshold is set to 1, raw stream orders (1, 2, 3…) are calculated. Higher threshold values mask non-stream cells as NoData and offset stream orders.

See also

This algorithm is a port of the Strahler stream order calculation from SAGA Channel Network and Drainage Basins tool.

Parameters

Basic parameters

Label	Name	Type	Description
Elevation raster	INPUT	[raster]	Digital Terrain Model raster layer
Minimum stream order threshold	THRESHOLD	[numeric: integer] Default: 1	Minimum stream order threshold
Strahler order	OUTPUT	[raster] Default: [Save to temporary file]	Specify the output Strahler order raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value	NODATA	[numeric: double] Default: -9999.0	Value to use for NoData cells in the output raster.
Creation options Optional	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Strahler order	OUTPUT	[raster]	The output Strahler order raster layer

Python code

Algorithm ID: native:strahlerorderfromdem

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.14. Strahler order from DEM and flow direction

Added in 4.4

Calculates Strahler stream order from an input elevation raster (DEM) and a pre-computed D8 flow direction raster.

D8 flow directions are computed internally to traverse channel trees topographically. Confluences of two stream channels of order N produce a downstream channel of order N + 1. When the threshold is set to 1, raw stream orders (1, 2, 3…) are calculated. Higher threshold values mask non-stream cells as NoData and offset stream orders.

See also

This algorithm is a port of the Strahler stream order calculation from SAGA Channel Network and Drainage Basins tool.

Parameters

Basic parameters

Label	Name	Type	Description
Elevation raster	INPUT	[raster]	Digital Terrain Model raster layer
Flow direction raster	INPUT_FLOW_DIRECTION	[raster]	raster layer representing flow directions
Minimum stream order threshold	THRESHOLD	[numeric: integer] Default: 1	Minimum stream order threshold
Strahler order	OUTPUT	[raster] Default: [Save to temporary file]	Specify the output Strahler order raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value	NODATA	[numeric: double] Default: -9999.0	Value to use for NoData cells in the output raster.
Creation options Optional	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Strahler order	OUTPUT	[raster]	The output Strahler order raster layer

Python code

Algorithm ID: native:strahlerorderfromflowdirection

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.15. Total curvature

Added in 4.0

Calculates the total curvature from an input raster layer. The curvature is the second derivative of the surface, revealing terrain features like ridges (positive curvature, convex) and valleys (negative, concave), with zero indicating flat or saddle points.

Fig. 24.81 Total curvature layer, showing concave (negative) surfaces in white, convex (positive) surfaces in blue, and near-flat areas in red

Parameters

Basic parameters

Label	Name	Type	Description
Elevation layer	INPUT	[raster]	Digital Terrain Model raster layer
Z factor	Z_FACTOR	[numeric: double] Default: 1.0	Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. Increasing the value of this parameter will exaggerate the final result (making it steeper). The default is 1 (no exaggeration).
Total curvature	OUTPUT	[raster] Default: [Save to temporary file]	Specify the output total curvature raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value	NODATA	[numeric: double] Default: -9999.0	Value to use for NoData cells in the output layer.
Creation options Optional	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Total curvature	OUTPUT	[raster]	The output total curvature raster layer

Python code

Algorithm ID: native:totalcurvature

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.16. Upslope area (from layer)

Added in 4.4

Calculates the combined upslope contributing area (catchments) for all target point locations provided in an input vector layer.

Each output raster cell value represents the percentage (0% to 100%) of surface flow originating at that cell that reaches at least one of the target points in the input vector layer. Various flow routing methods are supported. An optional sink routes raster layer can be provided to explicitly override topographic flow and direct water through karst features, culverts, or artificial depressions.

See also

This algorithm is a port of the SAGA Upslope Area tool.

Parameters

Basic parameters

Label	Name	Type	Description
Elevation	INPUT	[raster]	Input digital elevation model (DEM) raster layer.
Sink routes Optional	SINK_ROUTES	[raster]	Optional raster layer specifying explicit flow routes through sinks/depressions.
Method	METHOD	[enumeration] Default: 2	Flow routing methods: 0 — Deterministic 8: Single-flow direction algorithm, routing 100% of flow to the steepest downslope neighbor (O’Callaghan & Mark 1984). 1 — Deterministic Infinity: Continuous single-facet flow direction algorithm, routing flow along triangular facets using a 3×3 finite-difference aspect calculation (Tarboton 1997). 2 — Multiple Flow Direction: Divergent flow distribution to all lower-elevation neighbors, weighted by slope and a configurable convergence exponent (Freeman 1991, Quinn et al. 1991). 3 — Multiple Triangular Flow Direction: Advanced divergent routing utilizing 3D vector normal cross-products across triangular facets to distribute flow smoothly across complex terrain (Seibert & McGlynn 2007). 4 — Multiple Maximum Downslope Gradient Based Flow Direction: Adaptive MFD variant scaling exponent weights dynamically based on the local maximum gradient (Qin et al. 2011).
Convergence	CONVERGENCE	[numeric: double] Default: 1.1	Convergence factor for Multiple Flow Direction algorithms.
Use contour length weighting	MFD_CONTOUR	[boolean] Default: False	Include pseudo contour length weighting factor in multiple flow routing. Reduces flow to diagonal neighbour cells by a factor of 0.71 (see Quinn et al. 1991 for details).
Target point layer	INPUT	[vector: point]	Vector point layer containing target locations.
Upslope area	OUTPUT	[raster] Default: [Save to temporary file]	Specify the output upslope area raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value	NODATA	[numeric: integer] Default: -9999	Value to use for NoData cells in the output layer.
Creation options Optional	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Upslope area	OUTPUT	[raster]	The output upslope area raster layer.

Python code

Algorithm ID: native:upslopeareafromlayer

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

24.1.20.17. Upslope area (from point)

Added in 4.4

Calculates the upslope contributing area (catchment) for a given target coordinate point on a Digital Elevation Model (DEM).

Each output raster cell value represents the percentage (0% to 100%) of surface flow originating at that cell that drains to or passes through the target point. Various flow routing methods are supported. An optional sink routes raster layer can be provided to explicitly override topographic flow and direct water through karst features, culverts, or artificial depressions.

See also

This algorithm is a port of the SAGA Upslope Area tool.

Parameters

Basic parameters

Label	Name	Type	Description
Elevation	INPUT	[raster]	Input digital elevation model (DEM) raster layer.
Sink routes Optional	SINK_ROUTES	[raster]	Optional raster layer specifying explicit flow routes through sinks/depressions.
Method	METHOD	[enumeration] Default: 2	Flow routing methods: 0 — Deterministic 8: Single-flow direction algorithm, routing 100% of flow to the steepest downslope neighbor (O’Callaghan & Mark 1984). 1 — Deterministic Infinity: Continuous single-facet flow direction algorithm, routing flow along triangular facets using a 3×3 finite-difference aspect calculation (Tarboton 1997). 2 — Multiple Flow Direction: Divergent flow distribution to all lower-elevation neighbors, weighted by slope and a configurable convergence exponent (Freeman 1991, Quinn et al. 1991). 3 — Multiple Triangular Flow Direction: Advanced divergent routing utilizing 3D vector normal cross-products across triangular facets to distribute flow smoothly across complex terrain (Seibert & McGlynn 2007). 4 — Multiple Maximum Downslope Gradient Based Flow Direction: Adaptive MFD variant scaling exponent weights dynamically based on the local maximum gradient (Qin et al. 2011).
Convergence	CONVERGENCE	[numeric: double] Default: 1.1	Convergence factor for Multiple Flow Direction algorithms.
Use contour length weighting	MFD_CONTOUR	[boolean] Default: False	Include pseudo contour length weighting factor in multiple flow routing. Reduces flow to diagonal neighbour cells by a factor of 0.71 (see Quinn et al. 1991 for details).
Target point	INPUT	[coordinate]	Coordinate of the point defining the target cell. Press the … button next to the option and click on the canvas to fill the parameter with the clicked point coordinate.
Upslope area	OUTPUT	[raster] Default: [Save to temporary file]	Specify the output upslope area raster layer. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Output NoData value	NODATA	[numeric: integer] Default: -9999	Value to use for NoData cells in the output layer.
Creation options Optional	CREATION_OPTIONS	[string] Default: ‘’	For adding one or more creation options that control the raster to be created (colors, block size, file compression…). For convenience, you can rely on predefined profiles (see GDAL driver options section). Batch Process and Model Designer: separate multiple options with a pipe character (|).

Outputs

Label	Name	Type	Description
Upslope area	OUTPUT	[raster]	The output upslope area raster layer.

Python code

Algorithm ID: native:upslopeareafrompoint

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.