This tool calculates the plan curvature (i.e. contour curvature), or the rate of change in aspect along a contour line, from a digital elevation model (DEM). Curvature is the second derivative of the topographic surface defined by a DEM. Plan curvature characterizes the degree of flow convergence or divergence within the landscape (Gallant and Wilson, 2000). The user must input a DEM (`dem`). WhiteboxTools reports curvature in degrees multiplied by 100 for easier interpretation. The Z conversion factor (`zfactor`) is only important when the vertical and horizontal units are not the same in the DEM. When this is the case, the algorithm will multiply each elevation in the DEM by the Z Conversion Factor. If the DEM is in the geographic coordinate system (latitude and longitude), the following equation is used:

> zfactor = 1.0 / (111320.0 x cos(mid_lat))

where `mid_lat` is the latitude of the centre of the raster, in radians.

The algorithm uses the same formula for the calculation of plan curvature as Gallant and Wilson (2000). Plan curvature is negative for diverging flow along ridges and positive for convergent areas, e.g. along valley bottoms.

## Reference

Gallant, J. C., and J. P. Wilson, 2000, Primary topographic attributes, in Terrain Analysis: Principles and Applications, edited by J. P. Wilson and J. C. Gallant pp. 51-86, John Wiley, Hoboken, N.J.

## See Also

profile_curvature, tangential_curvature, total_curvature, slope, aspect

## Function Signature

`def plan_curvature(self, dem: Raster, log_transform: bool = False, z_factor: float = 1.0) -> Raster: ...`

## Project Links

WbW Homepage User Manual Support WbW