[Met_help] [rt.rap.ucar.edu #74813] History for Regrid Options
John Halley Gotway via RT
met_help at ucar.edu
Tue Jan 26 12:15:03 MST 2016
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Initial Request
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John, I am using the regrid option in grid_stat to remap my observation grid (Stage IV) to a specific FCST grid. In the documentation it says you can specify the grid definition in the to_grid parameter but it doesn't say the format to use. I assume it is something like this 255 3 342 210 20586 -122243 8 -96000 15000 15000 0 64 60000 30000 but I don't know the specific syntax to use?
Also, science question. I want to generate FSS stats for the output of our 4km ensemble compared to our 20km ensemble. The obs data is Stage IV. What is the smartest way to do this - should I remap the 20km FCST to the 4km FCST grid along with the OBS or should I remap the 20km and 4km to the OBS (Stage IV grid)?
Thanks
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Complete Ticket History
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Subject: Regrid Options
From: John Halley Gotway
Time: Thu Jan 21 10:23:25 2016
Bob,
I see that you're running Grid-Stat and are trying to use the
regridding
option included in the met-5.1 release. I think this is simpler than
you
expect. You don't need to explicitly specify the grid definition
yourself. Instead, all you need to put in the config file is
something
like this:
//
// Verification grid
//
regrid = {
to_grid = OBS; // Or use "FCST" to verify on the forecast grid.
vld_thresh = 0.5;
method = NEAREST;
width = 1;
}
Grid-Stat reads the forecast and observation files, extracts their
grid
information, and checks to see if they're the same. If not, it looks
in
the "to_grid" setting in the "regrid" section of the config file. If
it
says "FCST", it regrids the observation data onto the forecast grid.
If is
says "OBS", it puts the forecast on the observation grid. And there
are
some more options listed on page 46 of the User's Guide:
http://www.dtcenter.org/met/users/docs/users_guide/MET_Users_Guide_v5.1.pdf
FYI, the default regridding method is just nearest neighbor, as shown
above. You might want to use "BUDGET" for budget interpolation when
using
precip. Budget interpolation is designed to preserve mass better than
other methods, which is generally recommended for precip.
Lastly, I see you've asked the age-old question... regrid to the
higher-res
or lower-res domain? I don't have a good answer for you. People do
it
both ways for different reasons. Some folks prefer to evaluate on the
model domain, others prefer to use the observation domain so as not
to corrupt the obs with interpolation error. My guess is that more
people
would say evaluate on the 20km rather than the 4km because it's better
to
throw data points away than to create new ones through interpolation.
But
people do it both ways.
Hope that helps.
Thanks
John
On Thu, Jan 21, 2016 at 9:26 AM, robert.craig.2 at us.af.mil
<javascript:_e(%7B%7D,'cvml','robert.craig.2 at us.af.mil');> via RT <
met_help at ucar.edu <javascript:_e(%7B%7D,'cvml','met_help at ucar.edu');>>
wrote:
>
> Thu Jan 21 09:26:14 2016: Request 74813 was acted upon.
> Transaction: Ticket created by robert.craig.2 at us.af.mil
> <javascript:_e(%7B%7D,'cvml','robert.craig.2 at us.af.mil');>
> Queue: met_help
> Subject: Regrid Options
> Owner: Nobody
> Requestors: robert.craig.2 at us.af.mil
> <javascript:_e(%7B%7D,'cvml','robert.craig.2 at us.af.mil');>
> Status: new
> Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=74813 >
>
>
> John, I am using the regrid option in grid_stat to remap my
observation
> grid (Stage IV) to a specific FCST grid. In the documentation it
says you
> can specify the grid definition in the to_grid parameter but it
doesn't say
> the format to use. I assume it is something like this 255 3 342
210 20586
> -122243 8 -96000 15000 15000 0 64 60000 30000 but I don't know the
specific
> syntax to use?
>
> Also, science question. I want to generate FSS stats for the output
of
> our 4km ensemble compared to our 20km ensemble. The obs data is
Stage
> IV. What is the smartest way to do this - should I remap the 20km
FCST to
> the 4km FCST grid along with the OBS or should I remap the 20km and
4km to
> the OBS (Stage IV grid)?
>
> Thanks
>
>
>
------------------------------------------------
Subject: RE: [rt.rap.ucar.edu #74813] Regrid Options
From: robert.craig.2 at us.af.mil
Time: Thu Jan 21 10:57:12 2016
Thanks John, for some reason I missed page 46. The regrid option is
nice - makes it much easier.
Bob
-----Original Message-----
From: John Halley Gotway via RT [mailto:met_help at ucar.edu]
Sent: Thursday, January 21, 2016 11:23 AM
To: CRAIG, ROBERT J GS-12 USAF ACC 16 WS/WXN
Subject: [rt.rap.ucar.edu #74813] Regrid Options
Bob,
I see that you're running Grid-Stat and are trying to use the
regridding option included in the met-5.1 release. I think this is
simpler than you expect. You don't need to explicitly specify the
grid definition yourself. Instead, all you need to put in the config
file is something like this:
//
// Verification grid
//
regrid = {
to_grid = OBS; // Or use "FCST" to verify on the forecast grid.
vld_thresh = 0.5;
method = NEAREST;
width = 1;
}
Grid-Stat reads the forecast and observation files, extracts their
grid information, and checks to see if they're the same. If not, it
looks in the "to_grid" setting in the "regrid" section of the config
file. If it says "FCST", it regrids the observation data onto the
forecast grid. If is says "OBS", it puts the forecast on the
observation grid. And there are some more options listed on page 46
of the User's Guide:
http://www.dtcenter.org/met/users/docs/users_guide/MET_Users_Guide_v5.1.pdf
FYI, the default regridding method is just nearest neighbor, as shown
above. You might want to use "BUDGET" for budget interpolation when
using precip. Budget interpolation is designed to preserve mass
better than other methods, which is generally recommended for precip.
Lastly, I see you've asked the age-old question... regrid to the
higher-res or lower-res domain? I don't have a good answer for you.
People do it both ways for different reasons. Some folks prefer to
evaluate on the model domain, others prefer to use the observation
domain so as not to corrupt the obs with interpolation error. My
guess is that more people would say evaluate on the 20km rather than
the 4km because it's better to throw data points away than to create
new ones through interpolation. But people do it both ways.
Hope that helps.
Thanks
John
On Thu, Jan 21, 2016 at 9:26 AM, robert.craig.2 at us.af.mil
<javascript:_e(%7B%7D,'cvml','robert.craig.2 at us.af.mil');> via RT <
met_help at ucar.edu <javascript:_e(%7B%7D,'cvml','met_help at ucar.edu');>>
wrote:
>
> Thu Jan 21 09:26:14 2016: Request 74813 was acted upon.
> Transaction: Ticket created by robert.craig.2 at us.af.mil
> <javascript:_e(%7B%7D,'cvml','robert.craig.2 at us.af.mil');>
> Queue: met_help
> Subject: Regrid Options
> Owner: Nobody
> Requestors: robert.craig.2 at us.af.mil
> <javascript:_e(%7B%7D,'cvml','robert.craig.2 at us.af.mil');>
> Status: new
> Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=74813
> >
>
>
> John, I am using the regrid option in grid_stat to remap my
> observation grid (Stage IV) to a specific FCST grid. In the
> documentation it says you can specify the grid definition in the
to_grid parameter but it doesn't say
> the format to use. I assume it is something like this 255 3 342
210 20586
> -122243 8 -96000 15000 15000 0 64 60000 30000 but I don't know the
> specific syntax to use?
>
> Also, science question. I want to generate FSS stats for the output
> of our 4km ensemble compared to our 20km ensemble. The obs data
is
> Stage IV. What is the smartest way to do this - should I remap the
> 20km FCST to the 4km FCST grid along with the OBS or should I remap
> the 20km and 4km to the OBS (Stage IV grid)?
>
> Thanks
>
>
>
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