Geomorphometric Analysis using Whitebox Tool
Contents
Purpose
The purpose of this tutorial is to provide a clear and practical introduction to conducting a full geomorphometric analysis using WhiteboxTools within QGIS. This guide is designed for students, researchers, geoscientists, environmental analysts, and anyone working with terrain data. By following the step-by-step workflow, users will learn how to preprocess a DEM, extract primary and secondary terrain attributes, and visualize landforms using free, open-source tools. The resulting geomorphometric products can enhance understanding of the topography, structure, and processes shaping a study area, and are suitable for use in academic reports, research publications, and applied geospatial projects
Introduction
What is the geomorphometric
Geomorphometry is the science of quantitatively measuring and analyzing the physical features of the Earth’s surface. It focuses on extracting numerical parameters—such as slope, aspect, curvature, roughness, and landform indices—from Digital Elevation Models (DEMs). The goal is to describe terrain in a mathematically precise way, allowing researchers to model processes, compare landscapes objectively, and automate landform classification. In geomorphometry, every element of the terrain is expressed using measurable values, for example the slope expressed in degrees or percent rise, curvature expressed as concave or convex values, or drainage indices extracted using computational algorithms.
Advantages of Geomorphometric Analysis
Conducting a geomorphometric analysis offers major advantages for geomatics and environmental research. It transforms raw elevation data into quantifiable, reproducible metrics, enabling precise terrain interpretation that is impossible through visual observation alone. These quantitative outputs support a wide range of applications, including hydrological modeling, erosion assessment, landform classification, hazard mapping, suitability analysis, and machine-learning workflows. Because geomorphometric variables are standardized and scalable, they allow researchers and students to analyze landscapes efficiently, compare regions objectively, and produce high-quality results suitable for scientific publications or decision-making.
Advantage of Whitebox Tool for geomorphometric analysis
WhiteBox tool offers several significant advantages for performing geomorphometric analysis, particularly in an academic or research environment. As a free and open-source GIS processing library, it provides access to a wide range of terrain-analysis algorithms without the cost barriers associated with commercial software. WhiteboxTools is optimized for raster processing and uses efficient parallel computation, allowing users to work with large DEMs and complex workflows quickly and reliably. Its seamless integration with QGIS makes it easy for students and researchers to incorporate advanced geomorphometric tools into everyday GIS projects.
Another major advantage is the availability of specialized geomorphometry functions—such as curvature, ruggedness, topographic position, downslope indices, and feature-preserving smoothing—that are not always included in standard GIS packages. These tools help users extract meaningful quantitative metrics describing the shape and structure of the landscape. Because WhiteboxTools is actively maintained and scientifically oriented, it is ideal for teaching, research, hydrology, geomorphology, environmental modeling, and preparing high-quality outputs suitable for academic reports and publications.
Getting started
Plugin installation
To install the WhiteboxTools plugin in QGIS, the process begins by opening the Plugins menu and selecting Manage and Install Plugins. In the search bar, typing “Whitebox” displays the list of available Whitebox-related extensions. The correct plugin to install is WhiteboxTools for QGIS. If the plugin does not appear automatically, the standalone WhiteboxTools package must be downloaded from the official website: https://www.whiteboxgeo.com/download-whiteboxtools . After downloading, the folder containing the executable file ( whitebox_tools.exe ) should be extracted. Once installed, the path to the executable must be configured in QGIS: this is done by navigating to Settings → Options → Processing → Providers → WhiteboxTools, and selecting the extracted whitebox_tools.exe file as the executable. After this configuration is completed, the full suite of geomorphometric tools becomes available in the QGIS Processing Toolbox under WhiteboxTools
Data acquisition
For this tutorial, the elevation data are obtained from the Shuttle Radar Topography Mission (SRTM) using the USGS EarthExplorer portal. SRTM provides freely available digital elevation models at 1-arc-second (~30 m) resolution, which is sufficient for regional-scale geomorphometric analysis. The selected SRTM tile(s) covering the study area are downloaded from EarthExplorer, unzipped, and stored in the project workspace so they can be imported into QGIS and processed with WhiteboxTools.
Step-by-step: Downloading SRTM from EarthExplorer
Open the USGS EarthExplore website and Sign in with a USGS account (or create a free account if necessary) using the Login button in the top-right corner. In the Search Criteria tab, define the area of interest: Use the map to zoom to the study area and click Use Map; or enter coordinates or place names under Address/Place; or specify a polygon/rectangle using the Coordinate tools.
Set an appropriate Date Range (for SRTM, the default historical range is generally acceptable). Switch to the Data Sets tab and expand Digital Elevation → select SRTM → SRTM 1 Arc-Second Global. Click Results at the bottom of the interface. The list of available tiles for the defined area appears. In the results list, identify the tile(s) covering the study area and click the Download icon (downward arrow) for each. In the download options, choose the GeoTIFF (or equivalent DEM) format. Once the download is complete, extract the contents of the ZIP archive(s) into a dedicated project folder.
Fundamental Knowledge
Geomorphometric parameters derived using WhiteboxTools are computed from a Digital Elevation Model (DEM). For many tools, the Z conversion factor is an optional parameter. This factor is required only when the vertical and horizontal units of the DEM are different. This situation occurs when elevation values (Z) are expressed in one unit (for example, feet), while the spatial reference system of the DEM is expressed in another unit (such as meters or geographic coordinates in degrees).
This mismatch is common when using LiDAR-derived DEMs from the USGS, where elevation is often stored in feet while the horizontal projection is in meters. If geomorphometric derivatives are computed without applying the appropriate Z conversion factor under these conditions, the results will be geometrically inconsistent and physically incorrect.
For example, when elevation is in feet and horizontal units are in meters, the Z conversion factor must be set to 0.3048, since 1 foot = 0.3048 meters. Applying this correction ensures accurate slope, curvature, and terrain derivative calculations.
DEM Smoothing
When working with a Digital Elevation Model (DEM), it is important to keep in mind that many elevation datasets were created several years ago. As a result, it is common to encounter DEMs that contain noise, interpolation artifacts, or small irregularities caused by data acquisition and processing methods. In such cases, the Feature Preserving Smoothing tool available in the WhiteboxTools geomorphometric package can be used to reduce noise and enhance the visibility of true terrain features. This algorithm works by first calculating the 3D surface normal vectors for each grid cell based on a 3×3 neighborhood. The normal vector field is then smoothed by giving more weight to neighboring cells with similar orientation (lower angular difference), and the elevation values are updated using the smoothed normal vectors. This process effectively removes high-frequency noise while preserving important geomorphological structures such as ridges, valleys, and slope breaks.
To properly configure this tool, the key parameters to consider are the filter size, the normal difference threshold, and the number of iterations. Increasing the normal difference threshold increases the level of smoothing, because more neighboring values are included in the filtering process, generally resulting in a smoother surface.
The default filter size of 11 works well in many cases and provides a good balance between noise reduction and feature preservation. The Feature Preserving Smoothing tool can be accessed in QGIS by navigating through WhiteboxTools → Geomorphometric Analysis → FeaturePreservingSmoothing (fig. 2 to insert)
Local geomorphometric parameter
Slope
The slope describes how the terrain elevation varies across the landscape. It is expressed in degrees, radians, or percentage and represents the rate of maximum elevation change at each cell of a Digital Elevation Model (DEM). Slope is one of the most fundamental geomorphometric parameters because it directly controls many geomorphic and environmental processes. Steeper slopes generally experience greater erosion, faster surface runoff, and lower soil moisture, while flatter areas favor sediment accumulation and more stable landforms. Slope is also essential for identifying ridges, valley sides, plateaus, and areas prone to landslides or rapid hydrological flow.
To compute the slope in QGIS, open the WhiteboxTools plugin and navigate to Geomorphometric Analysis → Slope. The main input parameter is the DEM. The Z conversion factor must be applied only if the vertical and horizontal units of the DEM are different. The output type can be set to degrees (most commonly used), radians, or percent slope, depending on the application. These parameters ensure accurate and meaningful slope computation for geomorphometric analysis (fig. 3 To insert).
Hillshade
Hillshade is a black and white visualization of a Digital Elevation Model (DEM) that simulates how the terrain would appear if illuminated by a light source, typically representing the sun. It is computed using a specified azimuth (the horizontal direction of illumination, from 0° to 360°) and altitude (the vertical angle of the light source above the horizon). By modeling the interaction between light and topography, hillshade enhances the visual perception of relief, making variations in elevation, slope, ridges, valleys, and other landforms easier to identify.
Hillshade is a fundamental tool in geomorphometric analysis because it does not modify the DEM values, but instead improves terrain interpretation and visualization. It is particularly useful for identifying subtle landforms, drainage patterns, slope breaks, and structural lineaments that may not be immediately visible in raw elevation data. For best results, the azimuth should be chosen to illuminate the dominant terrain orientation of the area of interest, as certain landforms may appear more clearly when lit from specific directions. The altitude parameter controls the height of the light source; lower values emphasize shadows and relief, while higher values produce a smoother appearance. The Z conversion factor is optional and should only be applied when the vertical and horizontal units of the DEM differ.
To compute a hillshade in QGIS using WhiteboxTools, open the Whitebox Tools interface, navigate to Geomorphometric Analysis, and select Hillshade. Specify the input DEM, set the azimuth and altitude parameters according to the study area, adjust the Z conversion factor if required, and then run the tool to generate the hillshade raster.
In the left image (fig. 4 to insert), using an azimuth of 180° and an altitude of 25°, valley networks and linear depressions are strongly emphasized, making drainage patterns more apparent. In contrast, the right image, generated with an azimuth of 270° and an altitude of 45°, highlights convex landforms such as ridges and slope crests more clearly. By adjusting the azimuth and altitude values, users can selectively enhance different geomorphological features. Experimenting with these parameters allows for a better interpretation of terrain structure, improves landform recognition, and supports more accurate geomorphometric analysis.
Curvature
Curvature describes the local shape and orientation of a land surface and is a key quantity in geomorphometry. Using concepts from differential geometry, surface curvature provides a rigorous mathematical description of whether the terrain at a given point is convex, concave, or flat, based on the second derivative of elevation. In grid-based analysis, curvature is computed cell by cell by fitting a surface through each cell and its eight neighbors. Different curvature components capture different aspects of terrain form: profile curvature is measured in the direction of maximum slope and influences flow acceleration or deceleration along the slope, while plan curvature is measured perpendicular to the slope direction and affects the convergence or divergence of flow across the slope. Positive curvature values typically indicate convex surfaces (e.g., crests and spurs), negative values indicate concave surfaces (e.g., hollows and channels), and values near zero indicate planar surfaces. Because these patterns control water flow, erosion, soil development, and habitat conditions, curvature is one of the most important geomorphometric parameters for interpreting landforms and surface processes.
How to obtain curvature parameter
To extract curvature parameters in QGIS using WhiteboxTools, the process begins by opening the Processing Toolbox and navigating to WhiteboxTools → Geomorphometric Analysis, where all curvature-related tools are grouped. From there, the user selects the desired curvature type—for example MinCurvature, MaxCurvature, MeanCurvature, GaussianCurvature, ProfileCurvature, or PlanCurvature—depending on the geomorphometric analysis required. After selecting the tool, the dialog window opens → the user chooses the input DEM → sets the Z-scale factor if needed (usually 1 for meters) → specifies the output file location → and then runs the algorithm. The tool applies a second-derivative surface computation through the center cell and its neighbors → generates a curvature raster expressing convexity or concavity → and outputs a geospatial layer ready for visualization and interpretation in QGIS.
Directional relief
Landform Classification
Geomorphons
Geomorphons or geomorphologic phenotype are a representation of a landscape based on the difference in elevation between a each cell with its surronding, The Geomorphons are a way to vizualize the different landform type
