D8 Extreme Upslope Value

Title  D8 Extreme Upslope Value

Summary

Evaluates the extreme (either maximum or minimum) upslope value from an input grid based on the D8 flow model. This is intended initially for use in stream raster generation to identify a threshold of the slope times area product that results in an optimum (according to drop analysis) stream network.

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

By default, the tool checks for edge contamination. This is defined as the possibility that a result may be underestimated due to grid cells outside of the domain not being counted. This occurs when drainage is inwards from the boundaries or areas with no data values for elevation. The algorithm recognizes this and reports "no data" for the result for these grid cells. It is common to see streaks of "no data" values extending inwards from boundaries along flow paths that enter the domain at a boundary. This is the desired effect and indicates that the result for these grid cells is unknown due to it being dependent on terrain outside of the domain of data available. Edge contamination checking may be turned off in cases where you know this is not an issue or want to ignore these problems, if for example, the DEM has been clipped along a watershed outline.


Usage

Command Prompt Syntax:

mpiexec -n <number of processes> D8FlowPathExtremeUp -p<pfile> -sa <safile> -ssa <ssafile> [ -max] [ -nc] [ -o <outletfile>] [ -lyrname <layer name>] [ -lyrno <layer number>]

The default is maximum, that is switched to minimum if -min is specified.

pfile: File name for D8 flow direction grid (input)

safile: File name for slopearea file (input).

ssafile: File name for output grid with extreme upslope value

outletfile: input outlets file (OGR readable dataset)

nc: Flag for edge contamination

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.


Syntax

D8ExtremeUpslope (Input_D8_Flow_Direction_Grid, Input_Value_Grid, Use_maximum_upslope_value, Check_for_edge_contamination, {Input_Outlets}, Input_Number_of_Processes, Output_Extreme_Value_Grid)

Parameter Explanation Data Type
Input_D8_Flow_Direction_Grid Dialog Reference

A grid of D8 flow directions which are defined, for each cell, as the direction of the one of its eight adjacent or diagonal neighbors with the steepest downward slope.

 Raster Layer
Input_Value_Grid Dialog Reference

This is the grid of values of which the maximum or minimum upslope value is selected. The values most commonly used are the slope times area product needed when generating stream rasters according to drop analysis.

 Raster Layer
Use_maximum_upslope_value Dialog Reference

A flag to indicate whether the maximum or minimum upslope value is to be calculated.

 Boolean
Check_for_edge_contamination Dialog Reference

A flag that indicates whether the tool should check for edge contamination.

 Boolean
Input_Outlets (Optional) Dialog Reference

A point feature defining outlets of interest. If this input feature is used, only the area upslope of these outlets will be evaluated by the tool.

 Feature Layer
Input_Number_of_Processes Dialog Reference

The number of stripes that the domain will be divided into and the number of MPI parallel processes that will be spawned to evaluate each of the stripes.

 Long
Output_Extreme_Value_Grid Dialog Reference

A grid of the maximum/minimum upslope values.

 Raster Dataset

Code Samples

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