[GRASS-dev] Temporal GIS: best practice to access a map at a specific time?

GRASS GIS GRASS GIS developer
1

Hi all,

I’m working on a python module which compute superficial flows using simplified shallow water equations. It already works quite well and export results as temporal data sets.
But I’d like to add the possibility to work with temporal data sets as input (typically rainfall or other input flows).
I’ve looked at the documentation of the temporal module, but I haven’t figure out what would be the best way to access a strds at a specified time.
There might be something with get_registered_maps, but I don’t know how to select the map when the simulation time is between ‘start-time’ and ‘end-time’. I don’t know is SQL would be of any help here.

currently my program looks like this:

load grass maps as numpy arrays

while not sim_clock >= sim_duration:

calculate time-step duration
calculate flow and water depth

write results

register produced maps in space-time dataset

I was thinking of checking at the beginning of the while loop if there is the current input map is still valid for the current time-step, and ielse loading the new one. Does this approach make sense and how could I do that?

Thanks for your time.

Regards,
Laurent

2

On 22 May 2015 at 22:54, Laurent C. <lrntct@gmail.com> wrote:

Hi all,

Hi Laurent,

I try to answer to your question

I'm working on a python module which compute superficial flows using
simplified shallow water equations. It already works quite well and export
results as temporal data sets.
But I'd like to add the possibility to work with temporal data sets as input
(typically rainfall or other input flows).
I've looked at the documentation of the temporal module, but I haven't
figure out what would be the best way to access a strds at a specified time.
There might be something with get_registered_maps, but I don't know how to
select the map when the simulation time is between 'start-time' and
'end-time'. I don't know is SQL would be of any help here.

to get the registered maps for a period you can use t.rast.list using
the where option like "where=start-time>'2001-01-01 12:30:00' and
end-time<='2001-01-01 13:30:00' " or using the python function
tgis.list_maps_of_stds("strds", input, columns, order, where,
separator, method, header, granule)

currently my program looks like this:

************
load grass maps as numpy arrays

while not sim_clock >= sim_duration:
    calculate time-step duration
    calculate flow and water depth
    write results

register produced maps in space-time dataset
************

I was thinking of checking at the beginning of the while loop if there is
the current input map is still valid for the current time-step, and ielse
loading the new one. Does this approach make sense and how could I do that?

If I understand well your question, yes it should

Thanks for your time.

Regards,
Laurent

--
ciao
Luca

http://gis.cri.fmach.it/delucchi/
www.lucadelu.org

3

Hi Luca,

Sorry, I did not see your answer before. I actually solved my problems
some months ago.
Since my program is using internally numpy array, what I did is
creating a Class that stores an array alongside with start_time and
end_time. A method allows to check whether or not the array is still
"valid" using get_registered_maps_as_objects and a WHERE statement.

Thanks,
Laurent

2015-07-29 14:31 GMT-05:00 Luca Delucchi <lucadeluge@gmail.com>:

On 22 May 2015 at 22:54, Laurent C. <lrntct@gmail.com> wrote:

Hi all,

Hi Laurent,

I try to answer to your question

I'm working on a python module which compute superficial flows using
simplified shallow water equations. It already works quite well and export
results as temporal data sets.
But I'd like to add the possibility to work with temporal data sets as input
(typically rainfall or other input flows).
I've looked at the documentation of the temporal module, but I haven't
figure out what would be the best way to access a strds at a specified time.
There might be something with get_registered_maps, but I don't know how to
select the map when the simulation time is between 'start-time' and
'end-time'. I don't know is SQL would be of any help here.

to get the registered maps for a period you can use t.rast.list using
the where option like "where=start-time>'2001-01-01 12:30:00' and
end-time<='2001-01-01 13:30:00' " or using the python function
tgis.list_maps_of_stds("strds", input, columns, order, where,
separator, method, header, granule)

currently my program looks like this:

************
load grass maps as numpy arrays

while not sim_clock >= sim_duration:
    calculate time-step duration
    calculate flow and water depth
    write results

register produced maps in space-time dataset
************

I was thinking of checking at the beginning of the while loop if there is
the current input map is still valid for the current time-step, and ielse
loading the new one. Does this approach make sense and how could I do that?

If I understand well your question, yes it should

Thanks for your time.

Regards,
Laurent

--
ciao
Luca

http://gis.cri.fmach.it/delucchi/
www.lucadelu.org