r.param.scale(1grass)

💖 r.param.scale — the terrain-parameter extractor of your dreams 💖

okay bestie, listen up, because this one is a whole vibe. This is r.param.scale from the GRASS User's Manual (yes, r.param.scale(1grass), she's official 💅). What does she do? She extracts terrain parameters from a DEM, and she does it with a multi-scale approach — fitting quadratic parameters to any size window (via least squares). Iconic behaviour honestly.

✨ KEYWORDS ✨

raster, geomorphology, terrain, elevation, landform

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🌸 SYNOPSIS 🌸

r.param.scale
r.param.scale --help
r.param.scale [-c] input=name output=name  [slope_tolerance=float]
[curvature_tolerance=float]   [size=integer]   [method=string]
[exponent=float]   [zscale=float]   [--overwrite]  [--help]  [--verbose]
[--quiet]  [--ui]

🎀 Flags

• -c — Constrain model through central window cell
• --overwrite — Allow output files to overwrite existing files
• --help — Print usage summary
• --verbose — Verbose module output
• --quiet — Quiet module output
• --ui — Force launching GUI dialog

🦋 Parameters

• input=name [required] — Name of input raster map
• output=name [required] — Name for output raster map containing morphometric parameter
• slope_tolerance=float — Slope tolerance that defines a ’flat’ surface (degrees). Default: 1.0
• curvature_tolerance=float — Curvature tolerance that defines ’planar’ surface. Default: 0.0001
• size=integer — Size of processing window (odd number only). Options: 3-499. Default: 3
• method=string — Morphometric parameter in ’size’ window to calculate. Options: elev, slope, aspect, profc, planc, longc, crosc, minic, maxic, feature. Default: elev
• exponent=float — Exponent for distance weighting (0.0-4.0). Default: 0.0
• zscale=float — Vertical scaling factor. Default: 1.0

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💅 DESCRIPTION 💅

So r.param.scale extracts terrain parameters from a digital elevation model. She uses a multi-scale approach by fitting a bivariate quadratic polynomial to a given window size using least squares. No cap. 🫶

The module calculates the following parameters — and heads up, the terminology is from Wood, 1996, with related terminology used in other GRASS modules listed in brackets:

• elev — Generalised elevation value (for resampling purposes at different scale)
• slope — Magnitude of maximum gradient (steepest slope angle)
• aspect — Direction of maximum gradient (steepest slope direction = flow direction)
• profc — profile curvature (curvature intersecting with the plane defined by Z axis and maximum gradient direction). Positive values describe convex profile curvature, negative values concave profile curvature.
• planc — plan curvature (horizontal curvature, intersecting with the XY plane)
• longc — longitudinal curvature (profile curvature intersecting with the plane defined by the surface normal and maximum gradient direction)
• crosc — cross-sectional curvature (tangential curvature intersecting with the plane defined by the surface normal and a tangent to the contour — perpendicular to maximum gradient direction)
• maxic — maximum curvature (can be in any direction)
• minic — minimum curvature (in direction perpendicular to the direction of of maximum curvature)
• feature — Morphometric features: peaks, ridges, passes, channels, pits and planes

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👑 NOTES 👑

In r.param.scale the direction of maximum gradient (considered downslope) is stored as (West is 0 degree, East is +/- 180 degree):

• 0..+180 degree from West to North to East
• 0..-180 degree from West to South to East

⚠️ Note that the aspect map is calculated differently from r.slope.aspect. Do not come for me, I'm just the messenger. 💀

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🌈 EXAMPLE 🌈

The next commands will create a geomorphological map of the Spearfish sample dataset region:

g.region raster=elevation.10m -p
r.param.scale in=elevation.10m output=morphology method=feature size=9

Figure: Geomorphological map of a subregion in the Spearfish (SD) area

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😭 TODO 😭

• Fix bug when constrain through central cell option selected. (yeah girl, we know 🫠)
• Create color tables for all output files (presently only on features).

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📚 REFERENCES 📚

• Wood, J. (1996): The Geomorphological characterisation of Digital Elevation Models. Diss., Department of Geography, University of Leicester, U.K — online at: http://hdl.handle.net/2381/34503
• Java Code in LandSerf that implements the same procedure

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🔥 SEE ALSO 🔥

r.geomorphon, r.slope.aspect

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💖 AUTHORS 💖

Jo Wood - ASSIST’s home

Update to FP 3/2002: L. Potrich, M. Neteler, S. Menegon (ITC-irst)

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⭐ SOURCE CODE ⭐

Available at: r.param.scale source code (history)

Latest change: Friday Apr 17 01:04:26 2026 in commit: 32a143358df26b2e518b03c7e0d79541e8d1e5b1

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© 2003-2026 GRASS Development Team, GRASS 8.5.0 Reference Manual

and that's the whole page, bestie — r.param.scale(1grass) signing off from the GRASS 8.5.0 era, stay hydrated, go map some terrain 💜✨🦋