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53 lines
2.7 KiB
HTML
53 lines
2.7 KiB
HTML
<html>
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<head><link rel="stylesheet" type="text/css" href="help.css"/></head>
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<body>
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<h1 class='module'>Stream Definition By Threshold</h1>
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<div class='author'>(c) 2010 by David G. Tarboton</div>
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<div class='description'>Operates on any grid and outputs an indicator
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(1, 0) grid identifing cells with input values >= the threshold value. The
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standard use is to use an accumulated source area grid to as the input grid
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to generate a stream raster grid as the output. If you use the optional
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input mask grid, it limits the domain being evaluated to cells with mask
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values >= 0. When you use a D-infinity contributing area grid (*sca) as
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the mask grid, it functions as an edge contamination mask. The threshold
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logic is:</div>
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<pre align="center">src = ((ssa >= thresh) & (mask >= s0)) ? 1:0</pre>
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<h2>Parameters</h2>
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<dl class='parameters'>
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<dt>Number of Processes <div class='type'>Integer</div></dt>
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<dd>The number of stripes that the domain will be divided into and the
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number of MPI parallel processes that will be spawned to evaluate each
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of the stripes.</dd>
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<dt>Accumulated Stream Source Grid <div class='type'>Raster Grid</div></dt>
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<dd>This grid nominally accumulates some characteristic or combination
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of characteristics of the watershed. The exact characteristic(s) varies
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depending on the stream network raster algorithm being used. This grid
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needs to have the property that grid cell values are monotonically
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increasing downslope along D8 flow directions, so that the resulting
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stream network is continuous. While this grid is often from an accumulation,
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other sources such as a maximum upslope function will also produce a
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suitable grid.</dd>
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<dt>Mask Grid <div class='type'>Raster Grid (optional)</div></dt>
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<dd>This optional input is a grid that is used to mask the domain of
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interest and output is only provided where this grid is >= 0. A common
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use of this input is to use a D-Infinity contributing area grid as the
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mask so that the delineated stream network is constrained to areas where
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D-infinity contributing area is available, replicating the functionality
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of an edge contamination mask.</dd>
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<dt>Threshold <div class='type'>Double</div></dt>
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<dd>This parameter is compared to the value in the Accumulated Stream
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Source grid (*ssa) to determine if the cell should be considered a stream
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cell. Streams are identified as grid cells for which ssa value is >=
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this threshold.</dd>
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</dl>
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<h2>Outputs</h2>
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<dl class='parameters'>
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<dt>Stream Raster Grid <div class='type'>Raster Grid</div></dt>
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<dd>This is an indicator grid (1, 0) that indicates the location of
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streams, with a value of 1 for each of the stream cells and 0 for the
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remainder of the cells.</dd>
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</dl>
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</body></html>
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