[GRASS-dev] question about any July changes in hydrology functions

[Michael Barton]

I wanted to report that we managed to get rid of the artifacts and produce a
very nice looking map, with a 50-year recursive landscape evolution
simulation. 

Surprisingly, we ended up using a median filter after all, but without the
cutoff function. I realized that we needed to 'despeckle' the map in order
to remove the spikes that were the original problem we were trying to fix
when we generated the gridded peaks artifacts.

We're running more tests to see what neighborhood size works best. 7x7
looked really nice for most things, but was a little rough in areas where
grazing animals had randomly denuded cells of vegetation and it had
regenerated to a varying amount (though still far better than any other
result we'd had so far). Trying 9x9 now.

Also running it with the coupled agent based model of village farming over
the weekend to see how it performs.

I'll try to post some pictures of the results next week.

This updated version of r.landscape.evol is now on the GRASS Addons SVN
server.

Thanks to both of you for helping us to sort out this mysterious simulation
effect.

Michael


On 8/3/07 3:18 AM, "Glynn Clements" <glynn at gclements.plus.com> wrote:

> 
> Michael Barton wrote:
> 
>>>> 1. Is there any speed advantage/disadvantage to using r.mfilter over
>>>> r.neighbors? At the moment, because we are trying to get rid of occasional
>>>> spikes, I don't think that a weighted mean will give better results than an
>>>> unweighted mean. But the only way to get functions like a weighted mean is
>>>> to use r.mfilter, so it would be good to know if there are any known
>>>> performance hits or if it is faster.
>>> 
>>> r.mfilter currently works with integers. AFAICT, there's no
>>> fundamental reason why it can't be upgraded to FP.
>> 
>> Then, as is it won't work for us. If it can be upgraded to integers we can
>> try it.
> 
> I've added an FP version, r.mfilter.fp.
> 
> I didn't modify r.mfilter as it turns out that there is some behaviour
> which is specific to integer maps, and to the zero-is-null behaviour
> of 4.x. It wasn't practical to add support for FP and null values
> without breaking compatibility.

__________________________________________
Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton