Calc Flow Direction Map


This functor calculates a flow direction map using an elevation map.


Name Type Description
Elevation Map Type Elevation map. The elevation unit is not relevant.

Optional Inputs

Name Type Description Default Value
Diagonals Are Longer Boolean Value Type If true, the flow between diagonal cells is attenuated by the square root of two. True
Return All Directions Boolean Value Type If true, the functor returns the flow directions leaving a cell packed as a bitwise-OR combination of all possible directions. False
Use Lottery Boolean Value Type If true, the functor chooses randomly between possible directions. This flag only makes sense if the flag “Return All Directions” is false. False
Flow Also In Flat Areas Boolean Value Type If true, this functor also calculates flow direction for flat areas (zero slope cells). It is worth noting that, if a cell has eight neighbors with the same elevation, but at least one has flow direction, the flow will point toward that cell. True
Flow Direction Is Sparse Boolean Value Type If true, the map is loaded as a sparse image. Sparse images have the advantage of storing only the cells containing non-null values, but they have worse access time. False


Name Type Description
Flow Directions Map Type Flow direction map. Every non-null cell from this map contains a value indicating the direction toward the steepest slope (or the bit-wised combination of all possible directions, whether “Return All Directions” is true).



Null value elevation cells are ignored.

The values in the output map indicate the directions as follows:

32 64 128
16 x 1
8 4 2

where X is the current cell and the other cells indicate their corresponding position mask.

The resulting directions can be summed to pack several directions in a single value.

Internal Name