Re: making sense of r.reclass.area

On Mon, Nov 13, 2017 at 11:24 AM, Ken Mankoff <[email protected]> wrote:
>
> Dear GRASS list,
>
> I'm having trouble understanding how to properly use ~r.reclass.area~. It
seems to give inconsistent results. I'm using the following MWE to help me
figure this out.
>
> Several questions... such as:
>
> Why are the units in hectare instead of m^2?

Most probably for historical reasons (the module comes from GRASS 4).
>
> Why is -c and -d mutually exclusive for "mode=reclass" but not
"mode=rmarea"?

A bug. They should always be mutually exclusive: either input is already
clumped (-c flag), or clumps will be created from the input, considering
diagonal neighbours (-d flag).
>
> Why does mode=rmarea appear to ignore the -d flag

The -d flag only has an effect if clumps are created from the input. If the
-c flag is set, the input is already clumped and the -d flag has no
effect.  This is (should be) independent of the mode.

>
> Why does mode=reclass say it cannot find areas <=1 ha, but only if -c is
used, and the module never seems to have trouble finding areas of 1 ha
otherwise?

Maybe because the input is not clumped?

HTH,

Markus M
>
> Thanks,
>
>   -k.
>
>
> grass72 -c EPSG:3413 ./Gclump.debug
> # frink "1 hectare -> m^2" 10,000 m^2
> g.region w=0 e=500 s=0 n=500 res=100 -p
>
> debug() { r.out.xyz -i input=$@  | cut -d"|" -f3 | xargs -n5; }
>
> r.mapcalc "foo = if(row() == 2 && ((col() > 1) && (col() < 4)) , 1,
null())" --o
> r.mapcalc "foo = if(row() == 3 && col() == 4, 1, foo)" --o
> r.mapcalc "foo = if(row() == 4 && col() == 2, 1, foo)" --o
>
> debug foo
> # * * * * *
> # * 1 1 * *
> # * * * 1 *
> # * 1 * * *
> # * * * * *
>
> # RMAREA
>
> # simple run with no args
> r.reclass.area input=foo output=o value=1 mode=lesser method=rmarea --o
--q && debug o
> r.reclass.area -c input=foo output=o value=1 mode=lesser method=rmarea
--o --q && debug o
> # WANT: include diagonal
> r.reclass.area -d input=foo output=o value=1 mode=lesser method=rmarea
--o --q && debug o
> r.reclass.area -d -c input=foo output=o value=1 mode=lesser method=rmarea
--o --q && debug o
>
> # All produce the same output:
> # * * * * *
> # * 1 1 * *
> # * * * * *
> # * * * * *
> # * * * * *
>
> # RECLASS
>
> r.reclass.area input=foo output=o value=1 mode=lesser method=reclass --o
--q && debug o
> # GOOD: flags areas <=1. Does not consider diagonal:
> # * * * * *
> # * * * * *
> # * * * 1 *
> # * 1 * * *
> # * * * * *
>
> r.reclass.area -c input=foo output=o value=1 mode=lesser method=reclass
--o --q && debug o
> # ERROR: "No areas <= 1.000 hectar
>
> r.reclass.area -d input=foo output=o value=1 mode=lesser method=reclass
--o --q && debug o
> # Appears to work, only areas <=1 flagged, including diagonal
> # * * * * *
> # * * * * *
> # * * * * *
> # * 1 * * *
> # * * * * *
>
> r.reclass.area -c -d input=foo output=o value=1 mode=lesser
method=reclass --o --q && debug o
> # ERROR: flags c and d are mutually exclusive
>
> exit
> rm -fR  Gclump.debug
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