Steve on Image Processing

Concepts, algorithms & MATLAB

Results for: Upslope area

Upslope area – Summary

Posted by Steve Eddins,

Back in March I started writing about an algorithm implementation experiment for computing upslope area. Given an "image" whose pixel values are terrain elevations, the upslope area of a pixel is the area of the uphill terrain that drains through that pixel. I chose a paper that looked promising, and... read more >>

Upslope area – handling NaNs 2

Posted by Steve Eddins,

Since I originally posted my upslope toolbox to MATLAB Central back in August, I have heard from some experts about an issue related to NaNs in the DEM data. Specifically, some data sets record elevation only for DEM pixels within a particular catchment basin.... read more >>

Upslope area – vectorizing pixel flow calculations 2

Posted by Steve Eddins,

At the beginning of the upslope area series, I posted code showing how to compute the direction of maximum slope for a triangular facet, and how to compute the flow direction for a pixel. This purely scalar code ran fine, but more slowly than I wanted, so I decided... read more >>

Upslope area – influence and dependence maps

Posted by Steve Eddins,

In my August 7th post on upslope area, I showed how to construct and solve the flow matrix to determine the upslope area for every pixel in a digital elevation model (DEM). In addition, the flow matrix can be used to compute both the... read more >>

Upslope area – handling plateaus, revisited 5

Posted by Steve Eddins,

Earlier in this series I have discussed the problem of plateaus. Specifically, how do you assign a flow direction to a DEM pixel that has no downhill neighbors? I proposed in part 5 that the problem could be addressed by using the interpolation technique in roifill to modify... read more >>

Upslope area – Forming and solving the flow matrix 7

Posted by Steve Eddins,

About twelve years ago, I was implementing the algorithm that became roifill in the Image Processing Toolbox. In this algorithm, a specified set of pixels is replaced (or filled in) such that each of the replaced pixels equals the average of its north, east,... read more >>

Upslope area code is now available

Posted by Steve Eddins,

After my last upslope area post, I decided that I had enough of the algorithm details worked out to produce a set of working M-files. Although I have a few more posts to go, I've already uploaded the M-files to the MATLAB Central File Exchange. If you've been following this... read more >>

Upslope area – Recursive calculation procedure 6

Posted by Steve Eddins,

So far in this series I've talked about calculating pixel flow directions and handling plateaus, but I haven't yet discussed the actual upslope area calculation. The Tarboton paper presents a recursive formulation of the upslope area calculation (from page 313): ... read more >>