Rotor (rot) is a curvature of flow lines*. The unit of measurement is m-1.
Once elevations are given by , where x and y are plane Cartesian co-ordinates, rotor is a function of the partial derivatives of z:
where , , , , .
Rotor is a measure of twisting of flow lines. Flow lines turn clockwise when rot > 0, while flow lines turn anti-clockwise when rot < 0.
Like other local morphometric variables, rotor can be derived from a digital elevation model (DEM) by finite-difference methods (e.g., IF-2009 method and IF-1998 method) as well as the universal spectral analytical method.
Example**. A model of rotor was derived from a DEM of Mount Ararat by the universal spectral analytical method. The model includes 779,401 points (the matrix 1081 x 721); the grid spacing is 1". To deal with the large dynamic range of this variable, its values were logarithmically transformed. The vertical exaggeration of the 3D model is 2x. The data processing and modelling were carried out using the software Matlab R2008b.
* Shary, P.A., 1995. Land surface in gravity points classification by a complete system of curvatures. Mathematical Geology, 27: 373–390.
** Florinsky, I.V., 2017. An illustrated introduction to general geomorphometry. Progress in Physical Geography, 41: 723–752. doi pdf
For details and other examples, see: