D-Infinity Distance Down

Title  D-Infinity Distance Down

Summary

Calculates the distance downslope to a stream using the D-infinity flow model. The D-infinity flow model is a multiple flow direction model, because the outflow from each grid cell is proportioned between up to 2 downslope grid cells. As such, 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 different cells. The statistical method may be selected as the longest, shortest or weighted average of the flow path distance to the stream. Also one of several ways 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.


Usage

Command Prompt Syntax:

mpiexec -n <number of processes> DinfDistDown -ang <angfile> -fel <felfile> -src <srcfile> [ -wg <weightfile>] -dd <ddfile> [ -m ave h] [ -nc]

angfile: Input Dinf flow direction grid

felfile: Input pit filled elevation grid

srcfile: Input stream raster grid

wgfile: Input weight path grid

ddfile: Output distance down grid

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

average, min = minimum, and max = maximum)

nc: Flag for edge contamination


Syntax

DInfDistanceDown (Input_D-Infinity_Flow_Direction_Grid, Input_Pit_Filled_Elevation_Grid, Input_Stream_Raster_Grid, Statistical_Method, Distance_Method, Check_for_edge_contamination, {Input_Weight_Path_Grid}, Input_Number_of_Processes, Output_D-Infinity_Drop_to_Stream_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_Stream_Raster_Grid Dialog Reference

A grid indicating streams, by using a grid cell value of 1 on streams and 0 off streams. This is usually the output of one of the tools in the "Stream Network Raster" toolset.

 Raster Layer
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 ways 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. In the context of Distance Down this occurs when part of a flow path traced downslope from a grid cell leaves the domain without reaching a stream grid cell. With edge contamination checking selected, the algorithm recognizes this and reports no data for the result. 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 evaluate the distance using only the fraction of flow paths that terminate at a stream.

 Boolean
Input_Weight_Path_Grid (Optional) Dialog Reference

A grid giving weights (loadings) to be used in the distance calculation. This might be used for example where only flow distance through a buffer is to be calculated. The weight is then 1 in the buffer and 0 outside it. Alternatively the weight may reflect some sort of cost function for travel over the surface, perhaps representing travel time or attenuation of a process. If this input file is not used, the loadings will assumed to be one for each grid cell.

 Raster Layer
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_Drop_to_Stream_Grid Dialog Reference

Creates a grid containing the distance to stream calculated using the D-infinity flow model and the statistical and path methods chosen.

 Raster Dataset

Code Samples

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