About changing longitude array from 0 - 360 to -180 to 180 with Python xarray
I am a matlab user trying to use Python more for my computations recently. I am using xarray and would like to change my longitude array from 0 - 360 to -180 to 180 of a geophysical field. But when I do that:
df=xr.open_dataset(ecmwf_winds.nc)
u10=df['u10']
lon=df['longitude']
lon = np.where(lon > 180, lon-360, lon)
[X,Y]=np.meshgrid(lon,df.latitude)
plt.contourf(X,Y,u10)
the contourplot turns out to messy with gaps, which does not make sense. Can anyone please help me with it. I am not sure where I am doing wrong.
python python-xarray
asked Nov 16 '18 at 21:12
SMajSMaj
62
add a comment |
I am a matlab user trying to use Python more for my computations recently. I am using xarray and would like to change my longitude array from 0 - 360 to -180 to 180 of a geophysical field. But when I do that:
df=xr.open_dataset(ecmwf_winds.nc)
u10=df['u10']
lon=df['longitude']
lon = np.where(lon > 180, lon-360, lon)
[X,Y]=np.meshgrid(lon,df.latitude)
plt.contourf(X,Y,u10)
the contourplot turns out to messy with gaps, which does not make sense. Can anyone please help me with it. I am not sure where I am doing wrong.
python python-xarray
asked Nov 16 '18 at 21:12
SMajSMaj
62
you should covert the range of ALL you data to the new range, not just the ones above 180. so the linelon = np.where(lon > 180, lon-360, lon)should just belon=lon-180
– Gerges
Nov 16 '18 at 21:20
Thank you, but it does not seem to work. Its something to do with the field. However, somehow got around it. Thank you again.
– SMaj
Nov 19 '18 at 19:17
@GergesDib that's not right at all. longitudes from (-180 to 180) are not (0 to 360) - 180. The formula the OP has is correct - the data simply has to be sorted before it can be plotted.
– delgadom
Nov 26 '18 at 1:45
add a comment |
I am a matlab user trying to use Python more for my computations recently. I am using xarray and would like to change my longitude array from 0 - 360 to -180 to 180 of a geophysical field. But when I do that:
df=xr.open_dataset(ecmwf_winds.nc)
u10=df['u10']
lon=df['longitude']
lon = np.where(lon > 180, lon-360, lon)
[X,Y]=np.meshgrid(lon,df.latitude)
plt.contourf(X,Y,u10)
the contourplot turns out to messy with gaps, which does not make sense. Can anyone please help me with it. I am not sure where I am doing wrong.
python python-xarray
asked Nov 16 '18 at 21:12
SMajSMaj
62
I am a matlab user trying to use Python more for my computations recently. I am using xarray and would like to change my longitude array from 0 - 360 to -180 to 180 of a geophysical field. But when I do that:
df=xr.open_dataset(ecmwf_winds.nc)
u10=df['u10']
lon=df['longitude']
lon = np.where(lon > 180, lon-360, lon)
[X,Y]=np.meshgrid(lon,df.latitude)
plt.contourf(X,Y,u10)
the contourplot turns out to messy with gaps, which does not make sense. Can anyone please help me with it. I am not sure where I am doing wrong.
python python-xarray
python python-xarray
asked Nov 16 '18 at 21:12
SMajSMaj
62
asked Nov 16 '18 at 21:12
SMajSMaj
62
asked Nov 16 '18 at 21:12
SMajSMaj
62
asked Nov 16 '18 at 21:12
SMajSMaj
62
asked Nov 16 '18 at 21:12
SMajSMaj
62
62
you should covert the range of ALL you data to the new range, not just the ones above 180. so the linelon = np.where(lon > 180, lon-360, lon)should just belon=lon-180
– Gerges
Nov 16 '18 at 21:20
Thank you, but it does not seem to work. Its something to do with the field. However, somehow got around it. Thank you again.
– SMaj
Nov 19 '18 at 19:17
@GergesDib that's not right at all. longitudes from (-180 to 180) are not (0 to 360) - 180. The formula the OP has is correct - the data simply has to be sorted before it can be plotted.
– delgadom
Nov 26 '18 at 1:45
add a comment |
you should covert the range of ALL you data to the new range, not just the ones above 180. so the linelon = np.where(lon > 180, lon-360, lon)should just belon=lon-180
– Gerges
Nov 16 '18 at 21:20
Thank you, but it does not seem to work. Its something to do with the field. However, somehow got around it. Thank you again.
– SMaj
Nov 19 '18 at 19:17
@GergesDib that's not right at all. longitudes from (-180 to 180) are not (0 to 360) - 180. The formula the OP has is correct - the data simply has to be sorted before it can be plotted.
– delgadom
Nov 26 '18 at 1:45
you should covert the range of ALL you data to the new range, not just the ones above 180. so the line
lon = np.where(lon > 180, lon-360, lon) should just be lon=lon-180– Gerges
Nov 16 '18 at 21:20
you should covert the range of ALL you data to the new range, not just the ones above 180. so the line
lon = np.where(lon > 180, lon-360, lon) should just be lon=lon-180– Gerges
Nov 16 '18 at 21:20
Thank you, but it does not seem to work. Its something to do with the field. However, somehow got around it. Thank you again.
– SMaj
Nov 19 '18 at 19:17
Thank you, but it does not seem to work. Its something to do with the field. However, somehow got around it. Thank you again.
– SMaj
Nov 19 '18 at 19:17
@GergesDib that's not right at all. longitudes from (-180 to 180) are not (0 to 360) - 180. The formula the OP has is correct - the data simply has to be sorted before it can be plotted.
– delgadom
Nov 26 '18 at 1:45
@GergesDib that's not right at all. longitudes from (-180 to 180) are not (0 to 360) - 180. The formula the OP has is correct - the data simply has to be sorted before it can be plotted.
– delgadom
Nov 26 '18 at 1:45
add a comment |
2 Answers
2
active
oldest
votes
You need to assign the values as you've done and then also sort the resulting DataArray along the new coordinate values:
lon_name = 'longitude' # whatever name is in the data
# Adjust lon values to make sure they are within (-180, 180)
ds['_longitude_adjusted'] = xr.where(
ds[lon_name] > 180,
ds[lon_name] - 360,
ds[lon_name])
# reassign the new coords to as the main lon coords
# and sort DataArray using new coordinate values
ds = (
ds
.swap_dims({lon_name: '_longitude_adjusted'})
.sel(**{'_longitude_adjusted': sorted(ds._longitude_adjusted)})
.drop(lon_name))
ds = ds.rename({'_longitude_adjusted': lon_name})
answered Nov 25 '18 at 20:34
delgadomdelgadom
812718
It worked. Thank you very much.
– SMaj
Nov 26 '18 at 22:13
add a comment |
Another faster approach and much simpler approach without using where would be
df.coords['lon'] = (df.coords['lon'] + 180) % 360 - 180
df = df.sortby(df.lon)
Or it could be done in one line as
df['lon'] = ((df.lon + 180) % 360 - 180).sortby(df.lon)
Tip: For quick plotting you can use Xarrays inbuilt plotting function so you won't have to create a meshgrid.
df.u10.plot()
#or
df.u10.plt.contourf()
answered Nov 30 '18 at 16:18
Light_BLight_B
16310
Worked , thank you
– SMaj
Dec 4 '18 at 19:21
add a comment |
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2 Answers
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active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
You need to assign the values as you've done and then also sort the resulting DataArray along the new coordinate values:
lon_name = 'longitude' # whatever name is in the data
# Adjust lon values to make sure they are within (-180, 180)
ds['_longitude_adjusted'] = xr.where(
ds[lon_name] > 180,
ds[lon_name] - 360,
ds[lon_name])
# reassign the new coords to as the main lon coords
# and sort DataArray using new coordinate values
ds = (
ds
.swap_dims({lon_name: '_longitude_adjusted'})
.sel(**{'_longitude_adjusted': sorted(ds._longitude_adjusted)})
.drop(lon_name))
ds = ds.rename({'_longitude_adjusted': lon_name})
answered Nov 25 '18 at 20:34
delgadomdelgadom
812718
It worked. Thank you very much.
– SMaj
Nov 26 '18 at 22:13
add a comment |
You need to assign the values as you've done and then also sort the resulting DataArray along the new coordinate values:
lon_name = 'longitude' # whatever name is in the data
# Adjust lon values to make sure they are within (-180, 180)
ds['_longitude_adjusted'] = xr.where(
ds[lon_name] > 180,
ds[lon_name] - 360,
ds[lon_name])
# reassign the new coords to as the main lon coords
# and sort DataArray using new coordinate values
ds = (
ds
.swap_dims({lon_name: '_longitude_adjusted'})
.sel(**{'_longitude_adjusted': sorted(ds._longitude_adjusted)})
.drop(lon_name))
ds = ds.rename({'_longitude_adjusted': lon_name})
answered Nov 25 '18 at 20:34
delgadomdelgadom
812718
It worked. Thank you very much.
– SMaj
Nov 26 '18 at 22:13
add a comment |
You need to assign the values as you've done and then also sort the resulting DataArray along the new coordinate values:
lon_name = 'longitude' # whatever name is in the data
# Adjust lon values to make sure they are within (-180, 180)
ds['_longitude_adjusted'] = xr.where(
ds[lon_name] > 180,
ds[lon_name] - 360,
ds[lon_name])
# reassign the new coords to as the main lon coords
# and sort DataArray using new coordinate values
ds = (
ds
.swap_dims({lon_name: '_longitude_adjusted'})
.sel(**{'_longitude_adjusted': sorted(ds._longitude_adjusted)})
.drop(lon_name))
ds = ds.rename({'_longitude_adjusted': lon_name})
answered Nov 25 '18 at 20:34
delgadomdelgadom
812718
You need to assign the values as you've done and then also sort the resulting DataArray along the new coordinate values:
lon_name = 'longitude' # whatever name is in the data
# Adjust lon values to make sure they are within (-180, 180)
ds['_longitude_adjusted'] = xr.where(
ds[lon_name] > 180,
ds[lon_name] - 360,
ds[lon_name])
# reassign the new coords to as the main lon coords
# and sort DataArray using new coordinate values
ds = (
ds
.swap_dims({lon_name: '_longitude_adjusted'})
.sel(**{'_longitude_adjusted': sorted(ds._longitude_adjusted)})
.drop(lon_name))
ds = ds.rename({'_longitude_adjusted': lon_name})
answered Nov 25 '18 at 20:34
delgadomdelgadom
812718
edited Nov 26 '18 at 23:19
answered Nov 25 '18 at 20:34
delgadomdelgadom
812718
answered Nov 25 '18 at 20:34
delgadomdelgadom
812718
answered Nov 25 '18 at 20:34
delgadomdelgadom
812718
812718
It worked. Thank you very much.
– SMaj
Nov 26 '18 at 22:13
add a comment |
It worked. Thank you very much.
– SMaj
Nov 26 '18 at 22:13
It worked. Thank you very much.
– SMaj
Nov 26 '18 at 22:13
It worked. Thank you very much.
– SMaj
Nov 26 '18 at 22:13
add a comment |
Another faster approach and much simpler approach without using where would be
df.coords['lon'] = (df.coords['lon'] + 180) % 360 - 180
df = df.sortby(df.lon)
Or it could be done in one line as
df['lon'] = ((df.lon + 180) % 360 - 180).sortby(df.lon)
Tip: For quick plotting you can use Xarrays inbuilt plotting function so you won't have to create a meshgrid.
df.u10.plot()
#or
df.u10.plt.contourf()
answered Nov 30 '18 at 16:18
Light_BLight_B
16310
Worked , thank you
– SMaj
Dec 4 '18 at 19:21
add a comment |
Another faster approach and much simpler approach without using where would be
df.coords['lon'] = (df.coords['lon'] + 180) % 360 - 180
df = df.sortby(df.lon)
Or it could be done in one line as
df['lon'] = ((df.lon + 180) % 360 - 180).sortby(df.lon)
Tip: For quick plotting you can use Xarrays inbuilt plotting function so you won't have to create a meshgrid.
df.u10.plot()
#or
df.u10.plt.contourf()
answered Nov 30 '18 at 16:18
Light_BLight_B
16310
Worked , thank you
– SMaj
Dec 4 '18 at 19:21
add a comment |
Another faster approach and much simpler approach without using where would be
df.coords['lon'] = (df.coords['lon'] + 180) % 360 - 180
df = df.sortby(df.lon)
Or it could be done in one line as
df['lon'] = ((df.lon + 180) % 360 - 180).sortby(df.lon)
Tip: For quick plotting you can use Xarrays inbuilt plotting function so you won't have to create a meshgrid.
df.u10.plot()
#or
df.u10.plt.contourf()
answered Nov 30 '18 at 16:18
Light_BLight_B
16310
Another faster approach and much simpler approach without using where would be
df.coords['lon'] = (df.coords['lon'] + 180) % 360 - 180
df = df.sortby(df.lon)
Or it could be done in one line as
df['lon'] = ((df.lon + 180) % 360 - 180).sortby(df.lon)
Tip: For quick plotting you can use Xarrays inbuilt plotting function so you won't have to create a meshgrid.
df.u10.plot()
#or
df.u10.plt.contourf()
answered Nov 30 '18 at 16:18
Light_BLight_B
16310
edited Nov 30 '18 at 16:50
answered Nov 30 '18 at 16:18
Light_BLight_B
16310
answered Nov 30 '18 at 16:18
Light_BLight_B
16310
answered Nov 30 '18 at 16:18
Light_BLight_B
16310
16310
Worked , thank you
– SMaj
Dec 4 '18 at 19:21
add a comment |
Worked , thank you
– SMaj
Dec 4 '18 at 19:21
Worked , thank you
– SMaj
Dec 4 '18 at 19:21
Worked , thank you
– SMaj
Dec 4 '18 at 19:21
add a comment |
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you should covert the range of ALL you data to the new range, not just the ones above 180. so the line
lon = np.where(lon > 180, lon-360, lon)should just belon=lon-180– Gerges
Nov 16 '18 at 21:20
Thank you, but it does not seem to work. Its something to do with the field. However, somehow got around it. Thank you again.
– SMaj
Nov 19 '18 at 19:17
@GergesDib that's not right at all. longitudes from (-180 to 180) are not (0 to 360) - 180. The formula the OP has is correct - the data simply has to be sorted before it can be plotted.
– delgadom
Nov 26 '18 at 1:45