Performance difference in r.hydrodem

GRASS GRASS user
1

I am trying to understand the following observed difference in the performance of r.hydrodem using different options on the same input DEM (FCELL, 2500 x 2900 cells):

Case 1: “fast”, using the command with the -f, -c or -fc flags:
r.hydrodem -f input=inDEM output=outDEM
or
r.hydrodem -c input=inDEM output=outDEM
or
r.hydrodem -fc input=inDEM output=outDEM
completes in around or less than 12 seconds

Case 2: “slow”, passing no flags:
r.hydrodem input=inDEM output=outDEM
takes tens of minutes!

I could not find any explanation for this behavior in the documentation.

In both cases r.hydrodem identifies the same number of sinks.

Can this be because of some defaults being used in the absence of passed flags? In that case I could not figure out from the code which those could be.

I am using r.hydrodem installed today from the addon repo, so I guess it is the latest (docs: automatic markdownlint fixes (list indentation) (#1337) · OSGeo/grass-addons@7d78fe3 · GitHub)

Thanks!

2

I suspect the “least impact approach” is just more computationally demanding. The -f and -c flags disable it. But that’s all I can see, I haven’t looked into the specifics of the least impact approach.

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