Multiscale Signatures
Every terrain measure depends on the size of the neighbourhood you compute it over. A hummock is a bump at 10 metres and noise at 1 kilometre. Choosing one neighbourhood means choosing what you will see, and that choice is often arbitrary.
Multiscale Signatures removes the choice. These tools compute the same property over a whole range of neighbourhood sizes, then keep, for each cell, the scale at which the response is strongest and how strong it was. You get two rasters: the value, and the scale at which it occurred.
That second raster is the interesting one. It tells you the characteristic size of the feature each cell belongs to, which is how you separate a field ridge from a mountain range without deciding in advance which you are looking for.
Start here
Section titled “Start here”Max Elevation Deviation
Section titled “Max Elevation Deviation”The reference tool of this family, usually written DEVmax. It measures how far each cell sits above or below the mean of its neighbourhood, in standard deviations, and scans neighbourhood sizes from small to large.
The result marks the places that stand out most, at the scale where they stand out most: local knolls, terrace edges, broad plateaux, each at its own size.
Set the range of scales and the step between them. A wide range with a coarse step gives a quick overview, a narrow range with a fine step gives detail and takes longer.
Multiscale Roughness
Section titled “Multiscale Roughness”The same approach applied to surface roughness. It returns the maximum roughness found across the scale range and the scale where it occurred, which separates a locally broken surface from a smoothly undulating one.
Multiscale Topographic Position Image
Section titled “Multiscale Topographic Position Image”Packs three topographic position rasters, local, meso and broad, into a single colour image. Each channel carries one scale, so structures of different sizes appear in different colours in one picture. An excellent overview layer to open an analysis with.
The signature tools
Section titled “The signature tools”Four tools whose names end in Signature work differently. Rather than covering the whole raster, they take a set of point sites and produce an HTML report showing how the measure evolves with scale at each of those points.
Use them when you want to understand the terrain at specific locations, for instance to choose the right scale before running a full raster analysis.
All the tools
Section titled “All the tools”| Tool | What it does |
|---|---|
| Max Elevation Deviation | Maximum standardised elevation deviation across a range of scales, with the scale at which it occurs. |
| Max Difference From Mean | The same in elevation units rather than standard deviations. |
| Max Anisotropy Dev | Maximum directional anisotropy of elevation deviation across scales. |
| Multiscale Roughness | Maximum surface roughness across a range of neighbourhood scales. |
| Multiscale Curvatures | Curvatures and curvature based indices computed across scales. |
| Multiscale Elevation Percentile | The most extreme local elevation percentile found across scales. |
| Multiscale Elevated Index | Multiscale elevated index and its key scale raster, from Gaussian scale space residuals. |
| Multiscale Low Lying Index | The same for low lying positions, marking depressions and flats at their own scale. |
| Multiscale Std Dev Normals | Maximum spherical standard deviation of surface normals across scales, a multiscale roughness measure. |
| Multiscale Topographic Position Image | Packs local, meso and broad topographic position into one RGB image. |
| Max Elev Dev Signature | Elevation deviation against scale at point sites, as an HTML report. |
| Max Anisotropy Dev Signature | Anisotropy against scale at point sites, as an HTML report. |
| Multiscale Roughness Signature | Roughness against scale at point sites, as an HTML report. |
| Multiscale Std Dev Normals Signature | Spherical standard deviation against scale at point sites, as an HTML report. |
| Topographic Position Animation | An interactive HTML viewer and animated GIF of topographic position across scales. |
These are the heaviest tools in the toolbox. Each one runs the same analysis dozens of times. Clip your DEM to the area you care about, start with a coarse step between scales, and refine once you know what you are looking for.
Two outputs, one meaning. The value raster and the scale raster are read together. On their own, neither says much.