[GRASS-dev] G7: r.neighbors changes data type from CELL to DCELL

[Glynn Clements]

Markus Neteler wrote:

> in r59668 and r59669 I have fixed the issue that a map type
> (CELL/FCELL/DCELL) was not preserved as expected but always converted
> to DCELL.
> 
> Now CELL is generated for
> 
>     {c_count, w_count, NO_CATS, 0, 0, 1, "count", "count of non-NULL values"},
>     {c_divr, NULL, divr_cats, 0, 0, 1, "diversity",
>     {c_intr, NULL, intr_cats, 0, 0, 1, "interspersion",

Note that this change is incorrect for method=count when used with
weight=, as the result is the sum of the weights, which isn't
necessarily an integer.

Fixed in trunk in r59677.

> Remaining issues:
> 
> 1) "quantile=0.5" creeps into the history:
> 
> r.info landuse96_28m_mode7x7
> ...
>  |    r.neighbors input="landuse96_28m" output="landuse96_28m_mode7x7" met\   |
>  |    hod="mode" size=3 quantile=0.5
> 
> --> quantile=0.5 should not be there (even if ignored).

Remove the line:

    parm.quantile->answer = "0.5";

Optionally change:

	out->quantile = (parm.quantile->answer && parm.quantile->answers[i])
	    ? atof(parm.quantile->answers[i])
	    : 0;

to default to 0.5 rather than 0.

But given that we already a distinct "median" method, using
"quantile=0.5" is largely redundant.

> 2) The method=mode does not preserve CELL (likewise in r.series).
> 
> Any suggestion how to fix these two remaining problems?

You could just set is_int=1 (although that would make r59677
incorrect, as the weighted mode calulation does return an integer
result for integer values).

Using method=mode isn't particularly meaningful on floating-point
data, as the result is an artifact of the quantisation of the original
data. If measurement was perfectly accurate, every value should be
unique. This is largely why r.stats.zonal (formerly r.statistics2)
doesn't have method=mode.

Alternatively, replace the boolean is_int field with either a pointer
to a function which returns the result type based upon the input type
and whether weights are being used, or an enumeration (which would
either select such a function, or an equivalent block of code within a
switch statement).

-- 
Glynn Clements <glynn at gclements.plus.com>