4.2
Flow
Grid
Flow Direction outputs an encoded grid with the
neighboring cell direction to which the steepest descent is found using D8
algorithm [O'Callaghan and Mark (1984)]. The encoding is 1 - east, 2 - North
east, 3 - North, 4 - North west, 5 - West, 6 - South west, 7 - South, 8 - South
east.
Flow Accumulation outputs an accumulation grid that
contains the accumulated number of cells upstream of a cell, for each cell in
the input grid using a recursive procedure explained in (Mark,
1988).
Fig x.x shows the Flow direction and Flow accumulation calculations performed on a synthetic DEM grid.
In the Input section of the dialog browse the Pit
Filled Grid generated by the step 4.1. In the Output section browse the file
names to which the flow direction and flow accumulation grid could be saved. At
this point the module is ready to run; select Run to start processing. Please be
patient until it completes processing. The text browser at the bottom of the
dialog should provide information related to any error or processing. If the
Load in Data Frame is checked the Flow Direction Grid and Flow Accumulation Grid
will be automatically loaded in the Qgis window. After the processing is
complete you need to press Close to proceed to next
step.