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62 lines
3.3 KiB
HTML
62 lines
3.3 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'>D8 Extreme Upslope Value</h1>
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<div class='author'>(c) 2010 by David G. Tarboton</div>
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<div class='description'>Evaluates the extreme (either maximum or minimum)
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upslope value from an input grid based on the D8 flow model. This is intended
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initially for use in stream raster generation to identify a threshold of
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the slope times area product that results in an optimum (according to drop
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analysis) stream network.</div>
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<div class='description'>If the optional outlet point shapefile is used,
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only the outlet cells and the cells upslope (by the D8 flow model) of them
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are in the domain to be evaluated.</div>
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<div class='description'>By default, the tool checks for edge contamination.
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This is defined as the possibility that a result may be underestimated due
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to grid cells outside of the domain not being counted. This occurs when
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drainage is inwards from the boundaries or areas with no data values for
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elevation. The algorithm recognizes this and reports "no data"
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for the result for these grid cells. It is common to see streaks of
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"no data" values extending inwards from boundaries along flow
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paths that enter the domain at a boundary. This is the desired effect and
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indicates that the result for these grid cells is unknown due to it being
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dependent on terrain outside of the domain of data available. Edge
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contamination checking may be turned off in cases where you know this is
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not an issue or want to ignore these problems, if for example, the DEM has
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been clipped along a watershed outline.</div>
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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>D8 Flow Direction Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid of D8 flow directions which are defined, for each cell, as
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the direction of the one of its eight adjacent or diagonal neighbors
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with the steepest downward slope. This grid can be obtained as the
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output of the "D8 Flow Directions" tool.</dd>
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<dt>Upslope Values Grid <div class='type'>Raster Grid</div></dt>
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<dd>This is the grid of values of which the maximum or minimum upslope
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value is selected. The values most commonly used are the slope times
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area product needed when generating stream rasters according to drop
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analysis.</dd>
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<dt>Outlets Shapefile <div class='type'>Point Shapefile (optional)</div></dt>
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<dd>A point shape file defining outlets of interest. If this input file
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is used, only the area upslope of these outlets will be evaluated by
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the tool.</dd>
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<dt>Use maximum upslope value <div class='type'>Boolean</div></dt>
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<dd>A flag to indicate whether the maximum or minimum upslope value
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is to be calculated. Default is <strong>True</strong>.</dd>
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<dt>Check for edge contamination <div class='type'>Boolean</div></dt>
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<dd>A flag that indicates whether the tool should check for edge
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contamination. Default is <strong>True</strong>.</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>Extreme Value Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid of the maximum/minimum upslope values.</dd>
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</dl>
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</body></html>
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