# Peuker Douglas

(c) 2010 by David G. Tarboton
Creates an indicator grid (1, 0) of upward curved grid cells according to the Peuker and Douglas algorithm.
With this tool, the DEM is first smoothed by a kernel with weights at the center, sides, and diagonals. The Peuker and Douglas (1975) method (also explained in Band, 1986), is then used to identify upwardly curving grid cells. This technique flags the entire grid, then examines in a single pass each quadrant of 4 grid cells, and unflags the highest. The remaining flagged cells are deemed "upwardly curved", and when viewed, resemble a channel network. This proto-channel network generally lacks connectivity and requires thinning, issues that were discussed in detail by Band (1986).

1. Band, L. E., (1986), "Topographic partition of watersheds with digital elevation models", Water Resources Research, 22(1): 15-24.
2. Peuker, T. K. and D. H. Douglas, (1975), "Detection of surface-specific points by local parallel processing of discrete terrain elevation data", Comput. Graphics Image Process., 4: 375-387.

## Parameters

Number of Processes
Integer
  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 of the stripes.
Elevation Grid
Raster Grid
  A grid of elevation values. This is usually the output of the "Pit Remove" tool, in which case it is elevations with pits removed.
Center Smoothing Weight
Double
  The center weight parameter used by a kernel to smooth the DEM before the tool identifies upwardly curved grid cells. Default value is 0.4.
Side Smoothing Weight
Double
  The side weight parameter used by a kernel to smooth the DEM before the tool identifies upwardly curved grid cells. Default value is 0.1.
Diagonal Smoothing Weight
Double
  The diagonal weight parameter used by a kernel to smooth the DEM before the tool identifies upwardly curved grid cells. Default value is 0.05.

## Outputs

Stream Source Grid
Raster Grid
  An indicator grid (1, 0) of upward curved grid cells according to the Peuker and Douglas algorithm, and if viewed, resembles a channel network. This proto-channel network generally lacks connectivity and requires thinning, issues that were discussed in detail by Band (1986).