[GRASS-dev] t.rast.univar Unable to get statistics for raster map

[Veronica Andreo]

Hi,

El mié., 5 dic. 2018 a las 11:04, Moritz Lennert (<
mlennert at club.worldonline.be>) escribió:

> On 5/12/18 10:47, Margherita Di Leo wrote:
> > Hi,
> >
> > I have a strds and I try to get statistics for an area within a mask. A
> > couple of images have no data within the masked area, and t.rast.univar
> > gives the warning message:  "Unable to get statistics for raster map".
> > In the resulting csv, the missed dates are skipped, and this is sort of
> > unexpected and creates hurdles when for example I compare it with the
> > behavior of t.rast.what, that keeps the date and associates a no-data to
> > it. Wouldn't it be better if also t.rast.univar would yield a no-data
> > rather than skip the date?
>

+1

>
> This can probably somehow be solved within t.rast.univar, but IIUC the
> actual issue comes from the underlying r.univar call which has the same
> behaviour, for example when call with the 'zones' parameter and the '-t'
> flag: data is just absent if there are only null values in a given zone.
> I've been struggling with that, for example for addon modules such as
> i.segment.stats. I don't know how easy it would be to change that within
> r.univar, but it would be nice.
>
> IIUC, the issue comes from stats.c [1]:
>
> 123             if (stats[z].n == 0)
> 124                 continue;
>
> Maybe a flag to fill the stats with NULL values, instead of ignoring
> them, would be appropriate ?


+1!!

But I don't know what an good NULL value would be here.
>

IIRC, r.out.xyz and t.rast.out.xyz use the '*' character.
It would be good to create a ticket for this, no? As to not forget
afterwards...

my 0.01 cents
Vero
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