GRIB values manipulation - can it work this way?

[60north]

I try this ...

data, lats, lons = grb.data(lat1=20,lat2=70,lon1=0,lon2=28)
grb['values'] = data
msg = grb.tostring() 
grb = pygrib.fromstring(msg)
data = grb.values()

Script dies with:

File "./get_latest.py", line 81, in open_grib_get_area data= grb.values() File "pygrib.pyx", line 850, in pygrib.gribmessage.getattr (pygrib.c:8490) File "pygrib.pyx", line 1270, in pygrib.gribmessage.getitem (pygrib.c:14140) File "pygrib.pyx", line 1390, in pygrib.gribmessage._reshape_mask (pygrib.c:15560) ValueError: total size of new array must be unchanged

What else I should update in GRIB2, if I attempt writing a subset of the grid in a separate file? Sorry if this not a pygrib question.

[60north]

I found that grb['Ni'], grb['Nj'] are not updated automatically when you assign new values field to the message. Can it be the problem? numberOfValues, numberOfPoints are automatically updated and recalculated

[jswhit]

You can't write a subset back to the same file, since the grid definitions are now invalid. It would have worked if you did not create a subset of the grid. You need a template file that has the same grid, or create a grib2 file from scratch using ncepgrib2.Grib2Encode.

[60north]

Can I modify the grid definitions manually?

grb['Nj'] = data.shape[0] grb['Ni'] = data.shape[1]

and I preseume I would have to modify

latitudeOfFirstGridPointInDegrees longitudeOfFirstGridPointInDegrees

latitudeOfLastGridPointInDegrees longitudeOfLastGridPointInDegrees

?

2017-10-02 17:51 GMT+03:00 Jeff Whitaker [email protected]:

You can't write a subset back to the same file, since the grid definitions are now invalid. You need a template file that has the same grid, or create a grib2 file from scratch using ncepgrib2.Grib2Encode https://jswhit.github.io/pygrib/ncepgrib2_docs/ncepgrib2.Grib2Encode-class.html .

— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub https://github.com/jswhit/pygrib/issues/69#issuecomment-333558386, or mute the thread https://github.com/notifications/unsubscribe-auth/AMbusT2xvBIjGk6reO_uAeEdg3aFM18gks5soPiIgaJpZM4PqB2i .

-- С уважением, Федор Дружинин

Клуб Парусных Экспедиций 60ºN http://www.60north.ru

[60north]

Sorry if these are a GRIB newbie questions, I try to subset a huge HIRLAM GRIB, cnvgrib segfauls on it:) pygrib seems to be the only package that works so far

2017-10-02 18:00 GMT+03:00 Фёдор Дружинин [email protected]:

Can I modify the grid definitions manually?

grb['Nj'] = data.shape[0] grb['Ni'] = data.shape[1]

and I preseume I would have to modify

latitudeOfFirstGridPointInDegrees longitudeOfFirstGridPointInDegrees

latitudeOfLastGridPointInDegrees longitudeOfLastGridPointInDegrees

?

2017-10-02 17:51 GMT+03:00 Jeff Whitaker [email protected]:

You can't write a subset back to the same file, since the grid definitions are now invalid. You need a template file that has the same grid, or create a grib2 file from scratch using ncepgrib2.Grib2Encode https://jswhit.github.io/pygrib/ncepgrib2_docs/ncepgrib2.Grib2Encode-class.html .

— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub https://github.com/jswhit/pygrib/issues/69#issuecomment-333558386, or mute the thread https://github.com/notifications/unsubscribe-auth/AMbusT2xvBIjGk6reO_uAeEdg3aFM18gks5soPiIgaJpZM4PqB2i .

-- С уважением, Федор Дружинин

Клуб Парусных Экспедиций 60ºN http://www.60north.ru

-- С уважением, Федор Дружинин

Клуб Парусных Экспедиций 60ºN http://www.60north.ru

[jswhit]

No you can't modify the grid definition section with pygrib. If you don't have a template file with the right GDS defined, you need to create the whole grib message from scratch.

The grib writing capability of pygrib is very limited - you basically have to have a template grib file that allows you to just over-write the data and some of the simpler metadata (like the times).