Stream Definition By Threshold

Title  Stream Definition By Threshold

Summary

Operates on any grid and outputs an indicator (1,0) grid identifing cells with input values >= the threshold value. The standard use is to use an accumulated source area grid to as the input grid to generate a stream raster grid as the output. If you use the optional input mask grid, it limits the domain being evaluated to cells with mask values >= 0 . When you use a D-infinity contributing area grid (*sca) as the mask grid, it functions as an edge contamination mask. The threshold logic is: src = ((ssa >= thresh) & (mask >=0)) ? 1:0 .


Usage

Command Prompt Syntax:

mpiexec -n <number of processes> Threshold -ssa <ssafile> -src <srcfile> -thresh 100.0 [ -mask maskfile]

Default threshold value is 100.0

ssafile: File name for grid to be thresholded.

srcfile: File name for stream raster grid.

maskfile: File name for grid used to mask the output stream raster, or general thresholded grid.

thresh: Threshold parameter.

usemask: Flag to indicate whether maskfile has been input and is to be used (1 yes, 0 no)


Syntax

StreamDefByThreshold (Input_Accumulated_Stream_Source_Grid, {Input_Mask_Grid}, Threshold, Input_Number_of_Processes, Output_Stream_Raster_Grid)

Parameter Explanation Data Type
Input_Accumulated_Stream_Source_Grid Dialog Reference

This grid nominally accumulates some characteristic or combination of characteristics of the watershed. The exact characteristic(s) varies depending on the stream network raster algorithm being used. This grid needs to have the property that grid cell values are monotonically increasing downslope along D8 flow directions, so that the resulting stream network is continuous. While this grid is often from an accumulation, other sources such as a maximum upslope function will also produce a suitable grid.

 Raster Layer
Input_Mask_Grid (Optional) Dialog Reference

This optional input is a grid that is used to mask the domain of interest and output is only provided where this grid is >= 0. A common use of this input is to use a D-Infinity contributing area grid as the mask so that the delineated stream network is constrained to areas where D-infinity contributing area is available, replicating the functionality of an edge contamination mask.

 Raster Layer
Threshold Dialog Reference

This parameter is compared to the value in the Accumulated Stream Source grid (*ssa) to determine if the cell should be considered a stream cell. Streams are identified as grid cells for which ssa value is >= this threshold.

 Double
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_Stream_Raster_Grid Dialog Reference

This is an indicator grid (1,0) that indicates the location of streams, with a value of 1 for each of the stream cells and 0 for the remainder of the cells.

 Raster Dataset

Code Samples

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