Efficiently assign drainage directions over flat surfaces in digital elevation models
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richdem @ c762206



Title of Manuscript: An Efficient Assignment of Drainage Direction Over Flat Surfaces in Raster Digital Elevation Models

Authors: Richard Barnes, Clarence Lehman, David Mulla

Corresponding Author: Richard Barnes (rbarnes@umn.edu)

DOI Number of Manuscript 10.1016/j.cageo.2013.01.009

Code Repositories

Using This As A Tool

Don't. If you want to use these algorithms as an out-of-the-box terrain analysis system, please download RichDEM.

The Source Code

This repo references the RichDEM terrain analysis softare, of which these algorithms are all a part. main.cpp will run all of the algorithms mentioned above. The #include directives in main.cpp identify the necessary RichDEM libraries for using these implementations for your own work.


After cloning this repo you must acquire RichDEM by running:

git submodule init
git submodule update

To compile the programs run:


The result is a program called flats.exe.

The program is run by typing:

./flats.exe gentest <SIZE> <OUTPUT>
./flats.exe gentest 1000 test_dem.tif

./flats.exe <ALGORITHM> <INPUT> <OUTPUT>
./flats.exe 1 test_dem.tif barnes_out.tif
./flats.exe 2 test_dem.tif garbrecht_out.tif

The algorithms available are described briefly below and in greater detail in the manuscript.


This program reads in a digital elevation model (DEM) file specified on the command line. The file may be of any type recognised by GDAL. The program will run one of the algorithms described in the manuscript (and below), store the result in an output file, and report how long this took.


The two reference implementations output files in the D8 neighbour system to indicate flow directions. In this system all the flow from a central cell is directed to a single neighbour which is represented by a number according to the following system, where 0 indicates the central cell.


The output is in GeoTIFF format.

The Algorithms

This repository contains a reference implementation of the algorithms presented in the manuscript above. These implementations were used in performing speed comparison tests in the manuscript. The algorithms include

  • Algorithm 1: Barnes et al. (2014) The new algorithm presented in the above manuscript.

  • Algorithm 2: Garbrecht and Martz (1997) The eponymous algorithm against which the new algorithm is compared.

Generating Test Data

You can generate a test dataset which emphasises the speed differences between the two algorithms by running:

./flats.exe gentest <SIZE> test_dem.tif

This will generate a square DEM with a single outlet near the bottom-left corner.


Our implementation of Garbrecht and Martz (1997) attempts to reproduce the eponymous algorithm from the description in the eponymous paper. Note that this implementation does not apply itself iteratively, meaning that some flats will be unresolvable. The efficiency differences of even a single iteration of G&M (1997) are sufficient to support the argument in our manuscript.

The algorithms presented herein are part of the RichDEM code base, a collection of state of the art algorithms for quick terrain analysis. RichDEM is available at: https://github.com/r-barnes/richdem.

Suggested Test Procedure

You run tests similar to those discussed in the manuscript like so:

./flats.exe gentest 1000 test_dem.tif
./flats.exe 1 test_dem.tif barnes_out.tif
./flats.exe 2 test_dem.tif garbrecht_out.tif


Commit 131e21ef47ed4f97 (02016-09-14) and subsequent commits updated this repo to rely explicitly on the RichDEM codebase. This broadened the set of input/output formats available and synchronized the repo with the many benfits and standardizations introduced to RichDEM since this code was originally crafted.

The old codebase had the advantage of not relying on external libraries and being readily accessible to all parties. It had the disadvantage of being a slow, clumsy, and limited way to work with the data. The code now requires the use of the GDAL library, greatly expanding the data formats and data types which can be worked with, as well as greatly speeding up I/O.