====== Calc Flow Direction Map ======

===== Description =====

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

===== Inputs =====

^ 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  |

===== Outputs =====

^ 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).  |

===== Group =====

[[Functor List#Map Algebra | Map Algebra]]

===== Notes =====

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 =====

CalcFlowDirectionMap