TerraFlow Outputs

Sample dataset results | Experimental datasets results

The ultimate goal of flow modeling is computing indices that correctly estimate real phenomena. There is a large body of GIS literature concerned with issues involved in flow modeling on terrains. The focus of TerraFlow are the computational aspects of the indices rather than their suitability to the real phenomena. The accuracy of flow accumulation depends on the accuracy of the flow directions, and in particular on the accuracy of assigning flow directions on flat areas. As we have mentioned above, TerraFlow gives two choices for the computation of flow directions, SFD and MFD. From the computational point of view MFD and SFD do not make a (big) difference. In practice, it looks like MFD are natural on slopes, while SFD give better results on flat areas. MFD produces unconnected, divergent flow lines, while SFD produces convergent flow.

Sample Dataset Results

Consider the sample DEM, its plateaus (as computed by TerraFlow) and the flow accumulation computed by ArcInfo.


DEM

Plateaus

ArcInfo flow

Below we illustrate the results of running the different combinations of FILL and FLOW on the sample dataset. We show only the flow accumulation grids. The meaning of the combinations can be found in Features.


SFD_MFD

SFD_SFD

MFD_MFD

MFD_SFD


Arc_SFD

Arc_MFD

In addition to these the user can obtain even more flow accumulation results by experimenting with different -c thresholds.

Experimental Datasets Results

In order to investigate the performance of TerraFlow we performed experiments with different main memory sizes on a set of real-life terrains of various characteristics. The table below shows these datasets and some of TerraFlow's results on them.

Total running time of Terraflow at different main memory sizes. Data size is in million elements and running time is in hours.
Kaweah DEM MFD-MFD flow MFD-SFD flow
PuertoRico DEM PuertoRico MFD-MFD flow PuertoRico MFD-SFD flow
Sierra DEM Sierra MFD-MFD flow Sierra MFD-SFD flow
Hawaii DEM Hawaii MFD-MFD flow Hawaii MFD-SFD flow
Cumberlands DEM Cumberlands MFD-MFD flow Cumberlands MFD-SFD flow
LowerNE DEM LowerNE MFD-MFD flow LowerNE MFD-SFD flow
Usadem6 DEM Usadem6 MFD-MFD flow Usadem6 MFD-SFD flow

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Last modified: Mon May 14 18:14:40 2001 by laura.