Upslope area functions

Functions for computing and visualizing upslope area, influence map, dependence map

Description

A collection of functions for calculating the upslope area and related measurements for a digital elevation model (DEM).

Based on the method of Tarboton.

See also the upslope area postings on my image processing blog, March-August 2007, http://blogs.mathworks.com/steve.

Requires Image Processing Toolbox.

Functions include dem_flow, dependence_map, facet_flow, fill_sinks, flow_matrix, influence_map, pixel_flow, postprocess_plateaus, upslope_area, vis_dem_flow, and vis_map.

Includes a sample DEM data set.

• Required Products: Image Processing Toolbox
• MATLAB release: MATLAB 7.4 (R2007a)

[Wolfgang Schwanghart]

Hi Steve,

great contribution! Users of older Matlab versions (R14) need to replace the function hypot(s1,s2) by
s = sqrt(abs(s1).^2 + abs(s2).^2)

One critique: The functions don't handle NaNs.

Best regards, Wolfgang

[Steve Eddins]

Hi Wolfgang,

Do you have opinion about should be done with NaNs?

Thanks, Steve

[Wolfgang Schwanghart]

Hi Steve,

areas of interest to geographers often are catchments which commonly have irregular shape. Beyond the watersheds there is often a lack of data. Hence, these values outside the catchment are NaNs. While NaNs inside the catchment may be interpolated the NaNs outside can merely be extrapolated.

Hence, I tried following. I replaced the NaNs in the DEM by -Inf. That works except that it produces an erroneous flow direction on the watershed pixels.

Best regards,
Wolfgang

[Felix Hebeler]

After implementing Tarbotons Dinf algorithm for calculating flow directions I finally stumpled upon your toolbox, which is a lot faster. Thanks for the implementation, maybe if you add a keyword 'flow direction' it could save some other users some work ;-)

[Charlie seviour seviour]

How do you combine this script with flow data?
If the flow was the same for each pixel I could simply multiple the upslope area by a constant. Since this is not the case I need to find a way of inputting my flow data as it calculates the up slope area.

Can anyone enlighten me,
Charlie

[Bard R.]

Great algorithm, how would modify it to include flow length as well?

[Steve Eddins]

Bard, I am not doing any active algorithm development in this area right now, and I have no plans to enhance this submission. You might want to take a look at Wolfgang Schwanghart's TopoToolbox: http://physiogeo.unibas.ch/topotoolbox/