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84 lines
4.9 KiB
HTML
84 lines
4.9 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'>D-Infinity Distance Up</h1>
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<div class='author'>(c) 2010 by David G. Tarboton</div>
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<div class='description'>This tool calculates the distance from each grid
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cell up to the ridge cells along the reverse D-infinity flow directions.
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Ridge cells are defined to be grid cells that have no contribution from
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grid cells further upslope. Given the convergence of multiple flow paths
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at any grid cell, any given grid cell can have multiple upslope ridge cells.
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There are three statictical methods that this tool can use: maximum distance,
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minimum distance and waited flow average over these flow paths. A variant
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on the above is to consider only grid cells that contribute flow with a
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proportion greater than a user specified threshold (t) to be considered
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as upslope of any given grid cell. Setting t=0.5 would result in only one
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flow path from any grid cell and would give the result equivalent to a D8
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flow model, rather than D-infinity flow model, where flow is proportioned
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between two downslope grid cells. Finally there are several different
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optional paths that can be measured: the total straight line path (Pythagoras),
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the horizontal component of the straight line path, the vertical component
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of the straight line path, or the total surface flow path.</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>D-Infinity Flow Direction Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid giving flow direction by the D-infinity method. Flow direction
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is measured in radians, counter clockwise from east. This can be created
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by the tool "D-Infinity Flow Directions".</dd>
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<dt>Pit Filled Elevation Grid <div class='type'>Raster Grid</div></dt>
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<dd>This input is a grid of elevation values. As a general rule, it is
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recommended that you use a grid of elevation values that have had the
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pits removed for this input. Pits are generally taken to be artifacts
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that interfere with the analysis of flow across them. This grid can be
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obtained as the output of the "Pit Remove" tool, in which case
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it contains elevation values where the pits have been filled to the
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point where they just drain.</dd>
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<dt>Slope Grid <div class='type'>Raster Grid</div></dt>
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<dd>This input is a grid of slope values. This is measured as drop/distance
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and it is most often obtained as the output of the "D-Infinity
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Flow Directions" tool.</dd>
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<dt>Statistical Method <div class='type'>Choise</div></dt>
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<dd>Statistical method used to calculate the distance down to the stream.
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In the D-Infinity flow model, the outflow from each grid cell is
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proportioned between two downslope grid cells. Therefore, the distance
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from any grid cell to a stream is not uniquely defined. Flow that
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originates at a particular grid cell may enter the stream at a number
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of cells. The distance to the stream may be defined as the longest (maximum),
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shortest (minimum) or weighted average of the distance down to the stream.
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Default is <strong>Average</strong>.</dd>
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<dt>Distance Method <div class='type'>Choise</div></dt>
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<dd>Distance method used to calculate the distance down to the stream.
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One of several ways of measuring distance may be selected: the total
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straight line path (Pythagoras), the horizontal component of the straight
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line path (horizontal), the vertical component of the straight line path
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(vertical), or the total surface flow path (surface). Default is
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<strong>Horizontal</strong>.</dd>
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<dt>Proportion Threshold <div class='type'>Double</div></dt>
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<dd>The proportion threshold parameter where only grid cells that
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contribute flow with a proportion greater than this user specified
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threshold (t) is considered to be upslope of any given grid cell.
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Setting t=0.5 would result in only one flow path from any grid cell
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and would give the result equivalent to a D8 flow model, rather than
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D-Infinity flow model, where flow is proportioned between two downslope
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grid cells. Default <strong>0.5</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 determines whether the tool should check for edge
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contamination. This is defined as the possibility that a value may be
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underestimated due to grid cells outside of the domain not being counted.
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Default <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>D-Infinity Distance Up <div class='type'>Raster Grid</div></dt>
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<dd>Creates a grid containing the distances up to the ridge calculated
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using the D-Infinity flow model and the statistical and path methods
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chosen.</dd>
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</dl>
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</body></html>
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