Steve on Image Processing

Results for: Upslope area

Upslope area functions – updated files

Posted by Steve Eddins,

Upslope area functions – updated files For the geoscientists in the audience who are using my upslope area functions, I just updated the files. The update fixes a problem with the computation of influence and dependence maps for data sets that have NaNs outside the catchment area of interest. (Thanks to Claire for reporting... read more >>

Upslope area – Summary

Posted by Steve Eddins,

Upslope area – Summary  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,

Upslope area – handling NaNs  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... read more >>

Upslope area – vectorizing pixel flow calculations 2

Posted by Steve Eddins,

Upslope area – vectorizing pixel flow calculations  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,

Upslope area – influence and dependence maps  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... read more >>

Upslope area – handling plateaus, revisited 5

Posted by Steve Eddins,

Upslope area – handling plateaus, revisited  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,

Upslope area – Forming and solving the flow matrix  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... read more >>

Upslope area code is now available

Posted by Steve Eddins,

Upslope area code is now available  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,

Upslope area – Recursive calculation procedure  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 >>

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