[GRASSLIST:6128] Re: Problems with r.le.pixel !?

[Martin Wegmann]

Hello Sander, 

On Friday 11 March 2005 06:32, Sander Oom wrote:
> The output map still does not make sense thought, and IMHO it is wrong.

hmm, hard to tell where the problem lies - have you tried to compute b1,d1 
etc. as well (as far as I understood r.le.pixel it does not take longer to 
compute more indices) -- just to check if the senseless pattern persists. 

> A moving window analysis calculates a statistic for a certain window,
> puts the value of the statistic in the center cell of the window and
> then moves on cell up. Then the whole process repeats.

I think you understood it right but just to check, the calculated statistics 
for the window is put into the corresponding centre cell of a new (!) raster 
images, the values in the base image never change. 

> Thus the resulting map should show gradual changes in the statistic, as
> the moving window moved across the map. As the window moves a cell each
> time, the statistic is slightly changed by a new row of cells included
> in the window. This has to go gradually and should not show sharp edge!!

yes, but if your base image has sharp edges it will result in sharp dominance 
edges as well. As far as I can just your landcover.png it is classified and 
hence there might be sharp edges. 

> Running r.le.pixel on a slightly larger map showed dominance values in
> NODATA areas of the original map. Another tell tale sign something is
> wrong.

this sounds like a problem which I encountered before, I discussed it with 
Baker (the author of r.le) and send him a few error logs/images, but I 
haven't traced this problem anymore since then. 

> The ultimate aim is to run the moving window and then rescale to a
> larger cell size. The larger cell size used is the same as the moving
> window size!

Why you want to do that? The pixel value holds already the statistics of the 
larger cell size. If you rescale the cell size than you include values of a 
even larger area due to the moving window size. 

hope I understood you right and could help at least a bit, cheers, Martin

> Martin Wegmann wrote:
> > On Friday 11 March 2005 04:48, Sander Oom wrote:
> > [...]
> >
> >>http://www.oomvanlieshout.net/ftp/d3.png
> >>http://www.oomvanlieshout.net/ftp/landcover.png
> >>
> >>The d3 map seems to have three layers, but I can not figure out what
> >>they mean. There seems to be some sensible information in the
> >>background, but that is over ruled by the square pattern.
> >
> > why do you think d3 has three layers? To receive information concerning
> > the colour patterns just use d.legend.
> > The square pattern is caused by your sampling unit setup in r.le.setup -
> > you can choose circle or square and their size. If you set the sampling
> > unit to a smaller size (and to circles) your square pattern might
> > dissappear.
> >
> > cheers Martin

-- 
Martin Wegmann

DLR - German Aerospace Center
German Remote Sensing Data Center
@
Dept.of Geography
Remote Sensing and Biodiversity Unit
University of Wuerzburg
Am Hubland
97074 Würzburg

phone: +49-(0)931 - 888 4797
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