D-Infinity Distance Up

Title  D-Infinity Distance Up

Summary

This tool calculates the distance from each grid cell up to the ridge cells along the reverse D-infinity flow directions. Ridge cells are defined to be grid cells that have no contribution from grid cells further upslope. Given the convergence of multiple flow paths at any grid cell, any given grid cell can have multiple upslope ridge cells. There are three statictical methods that this tool can use: maximum distance, minimum distance and weighted flow average over these flow paths. A variant on the above is to consider only grid cells that contribute flow with a proportion greater than a user specified threshold (t) to be considered as upslope of any given grid cell. Setting t=0.5 would result in only one flow path from any grid cell and would give the result equivalent to a D8 flow model, rather than D-infinity flow model, where flow is proportioned between two downslope grid cells. There are several different options for the way distance can be measured: the total straight line path (Pythagoras), the horizontal component of the straight line path, the vertical component of the straight line path, or the total surface flow path. In the case of grids in a projected coordinate system, no unit conversions are done and the units are map units. Horizontal distances will be in the units of the grid cells and vertical distances in the units of the input elevation grid (fel). If these are inconsistent, then results will be incorrect for the case of mixed vertical and horizontal distances (Pythagoras, surface). In the case of grids in geograhic coordinates, a WGS84 spheroid is used to convert decimal degree cell sizes into meters for the computation of horizontal distances. Vertical distances remain in the units of the input elevation grid (fel), and mixed vertical and horizontal distances will be incorrect unless the vertical units are meters.


Usage

Command Prompt Syntax:

mpiexec -n <number of processes> DinfDistUp -ang <angfile> -fel <felfile> -slp <slpfile> -du <dufile> [-m <method> ] [ -thresh ] [ -nc]

angfile: Input Dinf flow direction grid

felfile: Input pit filled elevation grid

slpfile: Input slope grid

dufile: Output Dinf rise to ridge grid

method: Method to be used (Encoding is h = horizontal, v = vertical, p = Pythagoras, s = surface, ave =

average, min = minimum, and max = maximum)

thresh: Used to consider only grid cells that contribute flow with a proportion greater than a user

specified threshold.


Syntax

DInfDistanceUp (Input_D-Infinity_Flow_Direction_Grid, Input_Pit_Filled_Elevation_Grid, Input_Slope_Grid, Input_Proportion_Threshold, Statistical_Method, Distance_Method, Check_for_Edge_Contamination, Input_Number_of_Processes, Output_D-Infinity_Distance_Up_Grid)

Parameter Explanation Data Type
Input_D-Infinity_Flow_Direction_Grid Dialog Reference

A grid giving flow directions by the D-Infinity method. This is usually the output of the D-Infinity Flow Directions tool. Flow direction is measured in radians, counter clockwise from east. The algorithm is described in Tarboton, D. G., (1997), "A New Method for the Determination of Flow Directions and Contributing Areas in Grid Digital Elevation Models," Water Resources Research, 33(2): 309-319

 Raster Layer
Input_Pit_Filled_Elevation_Grid Dialog Reference

This input is a grid of elevation values. As a general rule, it is recommended that you use a grid of elevation values that have had the pits removed for this input. Pits are generally taken to be artifacts that interfere with the analysis of flow across them. This grid can be obtained as the output of the "Pit Remove" tool, in which case it contains elevation values where the pits have been filled to the point where they just drain.

 Raster Layer
Input_Slope_Grid Dialog Reference

This input is a grid of slope values. This is measured as drop/distance and it is most often obtained as the output of the "D-Infinity Flow Directions" tool.

 Raster Layer
Input_Proportion_Threshold Dialog Reference

The proportion threshold parameter where only grid cells that contribute flow with a proportion greater than this user specified threshold (t) is considered to be upslope of any given grid cell. Setting t=0.5 would result in only one flow path from any grid cell and would give the result equivalent to a D8 flow model, rather than D-infinity flow model, where flow is proportioned between two downslope grid cells.

 Double
Statistical_Method Dialog Reference

Statistical method used to calculate the distance down to the stream. In the D-infinity flow model, the outflow from each grid cell is proportioned between two downslope grid cells. Therefore, the distance from any grid cell to a stream is not uniquely defined. Flow that originates at a particular grid cell may enter the stream at a number of cells. The distance to the stream may be defined as the longest, shortest or weighted average of the distance down to the stream.

 String
Distance_Method Dialog Reference

Distance method used to calculate the distance down to the stream. One of several aspects of measuring distance may be selected: the total straight line path (Pythagoras), the horizontal component of the straight line path, the vertical component of the straight line path, or the total surface flow path.

 String
Check_for_Edge_Contamination Dialog Reference

A flag that determines whether the tool should check for edge contamination. This is defined as the possibility that a value may be underestimated due to grid cells outside of the domain not being counted. This occurs when drainage is inwards from the boundaries or areas with no data values for elevation. The algorithm recognizes this and reports no data for the value. It is common to see streaks of no data values extending inwards from boundaries along flow paths that enter the domain at a boundary. This is the desired effect and indicates that values for these grid cells is unknown due to it being dependent on terrain outside of the domain of data available. Edge contamination checking may be overridden in cases where you know this is not an issue or want to ignore these problems, if for example the DEM has been clipped along a watershed outline.

 Boolean
Input_Number_of_Processes Dialog Reference

This input indicates 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 piece of the domain.

 Long
Output_D-Infinity_Distance_Up_Grid Dialog Reference

Creates a grid containing the distances up to the ridge calculated using the D-infinity flow model and the statistical and path methods chosen. Units on the result are inherited from the horizontal or vertical units of the input grids used. See details in the summary.

 Raster Dataset

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