Dear Veronica
thank you for your answer
I understand your point but I still believe that the code is not working
properly for my aims
I try to explain myself with an example.
According to the example in the tutorial:
the first command creates a weekly mask based on my data (daily
precipitation in 2021):
t.rast.aggregate input=test2021 output=weekly_mask basename=mask_week
granularity="1 week" method=count nprocs=10
The second command add to the weekly value (7) the value of the
consecutive days in the week period
t.rast.algebra base=test_rr_maggiore_1mm
expression="test_consecutive_days_rr_maggiore_1mm = weekly_mask
{+,contains,l} if(test2021 < 1 && test2021[-1] < 1 || test2021[1] < 1 &&
test2021 < 1, 1, 0)" nprocs=10
In the attached file
https://drive.google.com/file/d/1eusufL8JLysac0wLfWC6oub0IM79e-KO/view?usp=sharing
I show an extract of the the values of a given pixel in the study area.
In the first week the value of the map
"test_consecutive_days_rr_maggiore_1mm is 10 (7 + 3). 7 is the weekly
base. 3 is the number of times in which a rainy day is preceded [-1] or
followed [+1] by another rainy day. This happen in 2021-01-05,
2021-01-09, 2021-01-10 (in fact 3 days).
What is not fitting my needs here is the fact that between the
2021-01-05 and 2021-01-09 there are other days without rainfall.
Actually we have not 3 consecutive days in this week!! We have 2
consecutive days: 2021-01-09, 2021-01-10 and another rainfall day at the
start of the week.
I would like to have, in this first week, the value of 9 (7+2) not 10
(7+3), because I'm interested in the annual maximum length of wet spell,
in days.
I hope I was able to explain myself
Thank you again
Ivan
On 18/08/22 15:36, Veronica Andreo wrote:
Hi Ivan,
It does indeed count consecutive days meeting a condition per week.
That's what the [-1] means in the t.rast.algebra command, i.e., it is
the temporal neighbourhood modifier. If you then want to get the
largest weekly consecutive days meeting the condition within a month
you can aggregate the "weekly_consecutive" time series with
t.rast.aggregate granularity="1 month" method="maximum"
HTH,
Vero
El jue, 18 ago 2022 a las 14:42, Ivan Marchesini
(<ivan.marches...@gmail.com>) escribió:
Hi Markus
thank you
Yes I saw that algorithm but, if I'm not wrong, it does not fit
with my
needs. The calculation made returns the number of days, in a given
interval (here week), that meets a certain condition. Not sure
they are
consecutive. As an example: if negative temperature occur in
monday and
thuesday and then in friday, saturday and sunday then the code
count 5
for that week. In my opinion what we need is 3.
I hope I was enough clear
In any case it would be good to find a solution for this type of
problem
because these type of indexes are used for climate data analysis
(e.g.:
https://www.ecad.eu/download/millennium/millennium.php
https://www.climdex.org/learn/indices/ )
thank you
Ivan
On 17/08/22 20:04, Markus Neteler wrote:
> Hi Ivan,
>
> On Wed, Aug 17, 2022 at 9:07 AM Ivan Marchesini
> <ivan.marches...@gmail.com> wrote:
>> Dear grass user
>>
>> I have daily rainfall strds
>>
>> I would like to obtain a layer of the largest number of
consecutive days
>> where rainfall >1 mm
> May this script code help?
>
https://grasswiki.osgeo.org/wiki/Temporal_data_processing#How_to_count_consecutive_days_that_meet_a_certain_condition?
>
> Markus
>
>> Do you have any suggestions on how to calculate this climate
index using
>> grass's time modules?
>>
>> thank you very much
>>
>> Ivan
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