Relative topographic position (RTP) is an index of local topographic position (i.e. how elevated or low-lying a site is relative to its surroundings) and is a modification of percent elevation range (PER; percent_elev_range) and accounts for the elevation distribution. Rather than positioning the central cell's elevation solely between the filter extrema, RTP is a piece-wise function that positions the central elevation relative to the minimum (zmin), mean (μ), and maximum values (zmax), within a local neighbourhood of a user-specified size (`filterx`, `filtery`), such that:

> RTP = (z0 − μ) / (μ − zmin), if z0 < μ

> OR

> RTP = (z0 − μ) / (zmax - μ), if z0 >= μ

The resulting index is bound by the interval [−1, 1], where the sign indicates if the cell is above or below than the filter mean. Although RTP uses the mean to define two linear functions, the reliance on the filter extrema is expected to result in sensitivity to outliers. Furthermore, the use of the mean implies assumptions of unimodal and symmetrical elevation distribution.

In many cases, Elevation Percentile (`ElevPercentile`) and deviation from mean elevation (`DevFromMeanElev`) provide more suitable and robust measures of relative topographic position.

## Reference

Newman, D. R., Lindsay, J. B., and Cockburn, J. M. H. (2018). Evaluating metrics of local topographic position for multiscale geomorphometric analysis. Geomorphology, 312, 40-50.

## See Also

`DevFromMeanElev`, `DiffFromMeanElev`, `ElevPercentile`, percent_elev_range

## Function Signature

`def relative_topographic_position(self, dem: Raster, filter_size_x: int = 11, filter_size_y: int = 11) -> Raster: ...`

## Project Links

WbW Homepage User Manual Support WbW