Grid Network

Creates 3 grids that contain for each grid cell: 1) the longest path, 2) the total path, and 3) the Strahler order number. These values are derived from the network defined by the D8 flow model.

The longest upslope length is the length of the flow path from the furthest cell that drains to each cell. The total upslope path length is the length of the entire grid network upslope of each grid cell. Lengths are measured between cell centers taking into account cell size and whether the direction is adjacent or diagonal.

Strahler order is defined as follows: A network of flow paths is defined by the D8 Flow Direction grid. Source flow paths have a Strahler order number of one. When two flow paths of different order join the order of the downstream flow path is the order of the highest incoming flow path. When two flow paths of equal order join the downstream flow path order is increased by 1. When more than two flow paths join the downstream flow path order is calculated as the maximum of the highest incoming flow path order or the second highest incoming flow path order + 1. This generalizes the common definition to cases where more than two flow paths join at a point.

Where the optional mask grid and threshold value are input, the function is evaluated only considering grid cells that lie in the domain with mask grid value greater than or equal to the threshold value. Source (first order) grid cells are taken as those that do not have any other grid cells from inside the domain draining in to them, and only when two of these flow paths join is order propagated according to the ordering rules. Lengths are also only evaluated counting paths within the domain greater than or equal to the threshold.

If the optional outlet point is used, only the outlet cells and the cells upslope (by the D8 flow model) of them are in the domain to be evaluated.

Command Prompt Syntax:

mpiexec -n <number of processes> Gridnet -p<pfile> -plen <plenfile> -tlen <tlenfile> -gord <gordfile> [-o <outletfile>] [-lyrname <layer name>] [-lyrno <layer number>] [-mask <maskfile> [-thresh <threshold>]]

pfile: D8 flow directions input file

plenfile: grid of longest flow length upstream of each point output file

tlenfile: grid of total path length upstream of each point output file

gordfile: grid of strahler order output file

outletfile: input outlets file (OGR readable dataset)

layer name: OGR layer name if outlets are not the first layer in outletfile (optional)

layer number: OGR layer number if outlets are not the first layer in outletfile (optional)

Layer name and layer number should not both be specified.

maskfile: mask file(optional)

threshold: Where a maskfile is input, there is an additional option to specify a threshold. This has to be immediately following the maskfile on the argument list. The grid network is evaluated for grid cells where values of the maskfile grid read as 4 byte integers are >= threshold.