Automating Multi-Directional Oblique Weighted Hillshade in QGIS with the Graphical Modeler

1. Background

Hill shading mimics how light interacts with a digital elevation model (DEM) from a hypothetical source, creating a greyscale image that enhances the perception of landforms (Horn, 1981; Yoeli, 1965). It produces a visual effect that helps improve understanding of terrain features. In many GIS projects, hillshade is the first product created from a DEM and often serves as the basis for subsequent cartographic work. Numerous derivatives, such as slope and curvature, are routinely derived from DEMs for geomorphometric analysis (Zevenbergen & Thorne, 1987). Standard hillshade, however, uses a single illumination azimuth (usually from the northwest) and altitude. This can cause directional bias, where slopes facing away from the light source become excessively dark, while illuminated slopes may lose micro-topographic detail. Multi-directional techniques address this by combining multiple hillshades generated from different azimuths. The MDOW approach uses oblique light directions and assigns weights to each, creating a more balanced, visually rich representation of terrain. Single-direction hillshades often overemphasize slopes facing away from the light source, causing noticeable directional artifacts. Multi-directional and oblique-weighted hillshades, like the Multi-Directional Oblique Weighted (MDOW) method originally popularized in the ArcGIS Terrain Tools toolbox, mitigate this issue by integrating hillshades from multiple azimuths (ESRI, 2015; Jenness, 2015). Recent work has also investigated alternative visualization methods that enhance or substitute traditional hillshade, especially for bathymetric and coastal data (Šolín et al., 2023). QGIS provides tools for MDOW hillshade, hillshade calculation, and raster algebra, but doing each step manually can be tedious and error-prone, especially when working with multiple DEM tiles. The QGIS Graphical Modeler allows users to connect algorithms into a single, custom workflow, enabling automated and reproducible creation of MDOW hillshades.

2. Data and software

The workflow is designed to be data-agnostic and can be applied to any single-band elevation raster with appropriate units and resolution. Typical inputs include national DEMs, LiDAR-derived surfaces, or SRTM-based products.

For this method, we used:

• Software: QGIS 3.44.3 with the Processing framework enabled.
• Input: DEM rasters in a projected coordinate system suitable for terrain analysis.
• Processing tools:
  • Raster terrain analysis → Hillshade (QGIS or GDAL implementation)
  • Raster → Raster calculator (GDAL)

The same steps can be adapted to other coordinate systems and DEM resolutions by adjusting the z-factor or scale parameters in the hillshade algorithm. The Graphical modeler in QGIS can be found by going to processing > Model Designer, and the Model Designer window should open as shown in Figure 1.