The D-infinity flow assignment model is illustrated in Figure 6‑25. Flows are assigned to two cells or pixels (coloured here in yellow) based on the direction of maximum gradient of the 8 triangular facets illustrated. The proportions assigned to each pixel are determined by the two ratios:

where α is defined in radians or degrees, as measured as in mathematics (i.e. from due east).

Figure 6‑25 D-Infinity flow assignment

In the D-infinity model, if the steepest slope vector angle illustrated lies outside of a facet (a special case that may well occur) then the direction vector is taken along the steepest edge of the facet.