[GRASS-user] help t.rast.algebra

Fri Sep 25 08:31:56 PDT 2015

```Hi,
Sorry, i am unable to help here, since the algebra is a deep mistery for me
as well. I think that after i have finished a paper about it, the algebra
will be much better documented.

Ciao
Sören
Am 25.09.2015 16:40 schrieb "Veronica Andreo" <veroandreo at gmail.com>:

> Hi Moritz,
>
> I eventually solved it like this:
>
> t.rast.aggregate -s input=cla granularity="1 years" method=minimum
> output=yearly_min basename=yearly_min
> t.rast.aggregate -s input=cla granularity="1 months" method=minimum
> output=monthly_min basename=monthly_min
>
> YEAR_I=2003 ; YEAR_F=2013
> MONTH_I=1 ;MONTH_F=12
>
> for YEAR in `seq \$YEAR_I \$YEAR_F` ; do
> for MONTH in `seq -w \$MONTH_I \$MONTH_F` ; do
> r.mapcalc expression="month_min_\${YEAR}_\${MONTH} =
> if(monthly_min_\${YEAR}_\${MONTH} == yearly_min_\${YEAR}, \${MONTH}, null())"
> --o
> done
> done
>
> r.series input=`g.list type=raster pattern=*_ag sep=,`
> output=month_of_min_mode method=mode
>
> Alternatively,
>
> 1. t.rast.aggregate -s input=cla granularity="1 months" method=minimum
> output=monthly_min basename=monthly_min
>
> 2. t.rast.aggregate -s input=monthly_min granularity="1 years"
> method=min_rast output=yearly_min_index
>
> 3. r.series input=`g.list rast pat=yearly_min_ind* sep=,` method=mode
>
> 4. r.reclass with
>
> 0 = 1
> 1 = 2
> 2 = 3
> 3 = 4
> 4 = 5
> 5 = 6
> 6 = 7
> 7 = 8
> 8 = 9
> 9 = 10
> 10 = 11
> 11 = 12
>
> Meanwhile, I still think t.rast.algebra should do the job in one
> command... I just cannot
> figure it out (yet) from the manual page:
> https://grass.osgeo.org/grass71/manuals/t.rast.algebra.html
>
> I keep studying it, though
>
> Thanks a lot!
> Vero
>
>
> 2015-09-24 3:58 GMT-03:00 Moritz Lennert <mlennert at club.worldonline.be>:
>
>> On 18/09/15 17:38, Veronica Andreo wrote:
>>
>>> Hi Soeren, list
>>>
>>> I need some help with t.rast.algebra. Well, if it is that my problem is
>>> really a t.rast.algebra problem...
>>>
>>> I have 2 strds with different granularities. A is an annual time series
>>> that contains the min annual temperature, B is a monthly time series
>>> containing the min monthly temperature. I want to compare the two of
>>> them, and when a pixel of B equals that of A, I need to get the
>>> start_month(B) but with the temporal resolution of A. So, what I want as
>>> output is a yearly time series containing the month in which the minimum
>>> temperature of each year occurs. Does that make any sense??
>>>
>>> I been studying t.rast.algebra all morning now and trying different kind
>>> of relationships (with no success), and I got lost in the different
>>> relationships and the different ways to express them.
>>>
>>> Can someone point me to the right way of using t.rast.algebra for this
>>> problem?
>>>
>>
>> No help for t.rast.algebra, but wouldn't looping over the years and
>> applying t.rast.series with method=min_raster get you what you want ?
>>
>> Moritz
>>
>
>
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