Calculate normal contour curvature (kn)c, which is the principal representative of the plan curvature group based on regression coefficients from the equation Z =ax^2+by^2+cxy+dx+ey(+f).

## Arguments

- a
regression coefficient

- b
regression coefficient

- c
regression coefficient

- d
regression coefficient

- e
regression coefficient

## References

Evans, I.S., 1980. An integrated system of terrain analysis and slope mapping. Zeitschrift f¨ur Geomorphologic Suppl-Bd 36, 274–295.

Wood, J., 1996. The geomorphological characterisation of digital elevation models (Ph.D.). University of Leicester.

Minár, J., Evans, I.S., Jenčo, M., 2020. A comprehensive system of definitions of land surface (topographic) curvatures, with implications for their application in geoscience modelling and prediction. Earth-Science Reviews 211, 103414. https://doi.org/10.1016/j.earscirev.2020.103414