gdaldem

Compute the hillshade of a DEM

$ gdaldem hillshade [path/to/input.tif] [path/to/output.tif]

$ gdaldem slope [path/to/input.tif] [path/to/output.tif]

$ gdaldem aspect [path/to/input.tif] [path/to/output.tif]

gdaldem mode input_dem output [options]

hillshade
    Mode: compute hillshaded relief from elevation

slope
    Mode: compute slope angle from elevation

aspect
    Mode: compute slope aspect (direction downhill)

color-relief
    Mode: apply color ramp to elevation using text file

TRI
    Mode: compute Topographic Ruggedness Index

TPI
    Mode: compute Topographic Position Index

roughness
    Mode: compute terrain roughness

-co "NAME=VALUE"
    Raster creation options (e.g., COMPRESS=LZW)

-b
    Select input band (default 1)

-z
    Vertical exaggeration factor (hillshade/slope, default 1)

-s
    Nominal ground resolution scale (default pixel size)

-az
    Azimuth of light (hillshade, degrees, default 315)

-alt
    Altitude of light (hillshade, degrees, default 45)

-alg
    Slope/aspect algorithm (default ZevenbergenThorne)

-combined
    Use multidirectional hillshade combination

-multidirectional
    Multi-directional hillshade

-p
    Slope output in percent rise (default degrees)

-zero_for_flat
    Return 0 for flat areas in aspect

color_file (for color-relief)
    Text file mapping elevation to RGB

-alpha
    Add alpha band for transparency (color-relief)

-compute_edges
    Force computation at edges

-q
    Quiet mode, suppress progress

-trigonometric
    Aspect in trigonometric convention (0-360)

-ig
    Ignore NoData on input

gdaldem is a versatile command-line utility from the GDAL (Geospatial Data Abstraction Library) suite, designed for processing Digital Elevation Models (DEMs) and other raster elevation data. It supports multiple modes to generate derived products essential for GIS analysis and cartography, including hillshade (simulated terrain shading), slope (terrain gradient), aspect (slope orientation), color-relief (elevation-colored maps), Topographic Ruggedness Index (TRI), Topographic Position Index (TPI), and roughness.

These operations enable quick visualization of terrain features, such as highlighting ridges, valleys, and steep areas. The tool processes large raster datasets efficiently, preserving geospatial metadata like projection and geotransform. Outputs are typically in formats like GeoTIFF, PNG, or JPEG, with customizable creation options. Mode-specific parameters adjust computations, e.g., scaling factors for accurate slope in different units or lighting angles for realistic hillshading.

Common workflows involve feeding processed outputs into QGIS, GRASS, or web mapping for enhanced terrain rendering. It's widely used in environmental modeling, hydrology, and remote sensing due to its speed and integration with GDAL's format support for hundreds of raster drivers.

Input must be elevation raster; NoData handling varies by mode. Color-relief requires valid text file format (elev r g b). Outputs may need projection alignment for overlays.

gdaldem hillshade -z 1.2 -s 111120 -az 315 input.tif output.tif

gdaldem color-relief input.tif colors.txt output.png -co PHOTOMETRIC=RGB -alpha

Lines like: nv 255 0 0
1000 0 255 0
2000 0 0 255 (elev r g b)

Part of GDAL since version 1.10 (2013), developed by Frank Warmerdam and community. Evolved with added modes like TRI/TPI in GDAL 2.x; now in GDAL 3.x for modern geospatial workflows.

gdal_translate(1), gdalwarp(1), gdalinfo(1), gdal_contour(1)