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89 lines
5.3 KiB
HTML
89 lines
5.3 KiB
HTML
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<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'>Grid Network</h1>
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<div class='author'>(c) 2010 by David G. Tarboton</div>
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<div class='description'>Creates 3 grids that contain for each grid cell:
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1) the longest path, 2) the total path, and 3) the Strahler order number.
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These values are derived from the network defined by the D8 flow model.</div>
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<div class='description'>The longest upslope length is the length of the
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flow path from the furthest cell that drains to each cell. The total upslope
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path length is the length of the entire grid network upslope of each grid
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cell. Lengths are measured between cell centers taking into account cell
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size and whether the direction is adjacent or diagonal.</div>
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<div class='description'>Strahler order is defined as follows: A network
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of flow paths is defined by the D8 Flow Direction grid. Source flow paths
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have a Strahler order number of one. When two flow paths of different order
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join the order of the downstream flow path is the order of the highest
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incoming flow path. When two flow paths of equal order join the downstream
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flow path order is increased by 1. When more than two flow paths join the
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downstream flow path order is calculated as the maximum of the highest
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incoming flow path order or the second highest incoming flow path order + 1.
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This generalizes the common definition to cases where more than two flow
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paths join at a point.</div>
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<div class='description'>Where the optional mask grid and threshold value
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are input, the function is evaluated only considering grid cells that lie
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in the domain with mask grid value greater than or equal to the threshold
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value. Source (first order) grid cells are taken as those that do not have
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any other grid cells from inside the domain draining in to them, and only
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when two of these flow paths join is order propagated according to the
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ordering rules. Lengths are also only evaluated counting paths within the
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domain greater than or equal to the threshold.</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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<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>Outlets Shapefile <div class='type'>Point Shapefile (optional)</div></dt>
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<dd>A point shapefile defining the outlets of interest. If this input
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file is used, only the cells upslope of these outlet cells are considered
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to be within the domain being evaluated.</dd>
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<dt>Mask Grid <div class='type'>Raster Grid (optional)</div></dt>
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<dd>A grid that is used to determine the domain do be analyzed. If the
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mask grid value >= mask threshold (see below), then the cell will be
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included in the domain. While this tool does not have an edge contamination
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flag, if edge contamination analysis is needed, then a mask grid from
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a function like AreaD8 that does support edge contamination can be used
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to achieve the same result.</dd>
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<dt>Mask Threshold Value <div class='type'>Double (optional)</div></dt>
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<dd>This input parameter is used in the calculation mask grid value
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>= mask threshold to determine if the grid cell is in the domain to
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be analyzed. Default value is <strong>100</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>Strahler Network Order Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid giving the Strahler order number for each cell. A network
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of flow paths is defined by the D8 Flow Direction grid. Source flow
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paths have a Strahler order number of one. When two flow paths of
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different order join the order of the downstream flow path is the
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order of the highest incoming flow path. When two flow paths of equal
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order join the downstream flow path order is increased by 1. When more
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than two flow paths join the downstream flow path order is calculated
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as the maximum of the highest incoming flow path order or the second
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highest incoming flow path order + 1. This generalizes the common
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definition to cases where more than two flow paths join at a point.</dd>
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<dt>Longest Upslope Length Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid that gives the length of the longest upslope D8 flow path
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terminating at each grid cell. Lengths are measured between cell centers
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taking into account cell size and whether the direction is adjacent
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or diagonal.</dd>
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<dt>Total Upslope Length Grid <div class='type'>Raster Grid</div></dt>
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<dd>The total upslope path length is the length of the entire D8 flow
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grid network upslope of each grid cell. Lengths are measured between
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cell centers taking into account cell size and whether the direction
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is adjacent or diagonal.</dd>
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</dl>
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</body></html>
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