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我使用 ERA5 数据集来绘制南部非洲垂直速度的横截面。可在此处找到数据样本。我尝试复制此处给出的示例，但是，cross_section 函数不起作用，因为数据集的坐标中缺少信息。我使用的代码如下：

from matplotlib import pyplot
from matplotlib.cm import get_cmap
from __future__ import print_function
from netCDF4 import Dataset,num2date,date2num
from matplotlib.colors import from_levels_and_colors
from cartopy import crs
from cartopy.feature import NaturalEarthFeature, COLORS
from metpy.units import units
from datetime import datetime
from metpy.plots import StationPlot
from metpy.interpolate import cross_section
from PIL import Image, ImageDraw
from mpl_toolkits.basemap import Basemap
from mpl_toolkits.axes_grid1 import ImageGrid
#
import os
import netCDF4 as nc
import scipy.spatial as ss
import matplotlib.pyplot as plt
import metpy.calc as mpcalc
import xarray as xr
import cartopy.crs as ccrs
import matplotlib
import numpy as np
import datetime
import cartopy.feature as cfeature
import matplotlib.gridspec as gridspec
import scipy.ndimage as ndimage
#
root_dir = '/users/.../my_var/'
#
data = xr.open_dataset('omega.nc')
data = data.metpy.parse_cf().squeeze()
print(data)
#

数据如下：

<xarray.Dataset>
Dimensions:    (bnds: 2, latitude: 161, level: 16, longitude: 137)
Coordinates:
    time       datetime64[ns] 2005-02-01
  * longitude  (longitude) float32 8.0 8.25 8.5 8.75 ... 41.25 41.5 41.75 42.0
  * latitude   (latitude) float32 -5.0 -5.25 -5.5 -5.75 ... -44.5 -44.75 -45.0
  * level      (level) float64 100.0 150.0 200.0 250.0 ... 750.0 800.0 850.0
    metpy_crs  object Projection: latitude_longitude
Dimensions without coordinates: bnds
Data variables:
    time_bnds  (bnds) datetime64[ns] 2005-01-01 2005-12-01
    w          (level, latitude, longitude) float32 -0.001213 ... 0.003879
Attributes:
    CDI:          Climate Data Interface version 1.9.7.1 (http://mpimet.mpg.d...
    Conventions:  CF-1.6
    history:      Fri Feb 04 23:12:51 2022: cdo yearmean omega_SAF_DJF_1986_2...
    frequency:    year
    CDO:          Climate Data Operators version 1.9.7.1 (http://mpimet.mpg.d...

继续提供我想要横截面的坐标：

start = (-7, 17)
end = (-28, 17)
cross = cross_section(data, start, end).set_coords(('latitude', 'longitude'))

最终，cross_section 函数产生以下错误消息，与缺少有关 ERA5 坐标的信息有关：

Traceback (most recent call last):
  File "/users/pr007/mkaryp/.local/lib/python3.6/site-packages/metpy/interpolate/slices.py", line 167, in cross_section
    x = data.metpy.x
  File "/users/pr007/mkaryp/.local/lib/python3.6/site-packages/metpy/xarray.py", line 431, in x
    return self._axis('x')
  File "/users/pr007/mkaryp/.local/lib/python3.6/site-packages/metpy/xarray.py", line 385, in _axis
    raise AttributeError(axis + ' attribute is not available.')
AttributeError: x attribute is not available.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/users/pr007/mkaryp/.local/lib/python3.6/site-packages/metpy/interpolate/slices.py", line 157, in cross_section
    interp_type=interp_type)
  File "/users/pr007/mkaryp/.local/lib/python3.6/site-packages/xarray/core/dataset.py", line 4592, in map
    for k, v in self.data_vars.items()
  File "/users/pr007/mkaryp/.local/lib/python3.6/site-packages/xarray/core/dataset.py", line 4592, in <dictcomp>
    for k, v in self.data_vars.items()
  File "/users/pr007/mkaryp/.local/lib/python3.6/site-packages/metpy/interpolate/slices.py", line 169, in cross_section
    raise ValueError('Data missing required coordinate information. Verify that '
ValueError: Data missing required coordinate information. Verify that your data have been parsed by MetPy with proper x and y dimension coordinates and added crs coordinate of the correct projection for each variable.

关于解决方法的任何帮助？

谢谢！

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1 回答 1

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从您的数据集输出中可以看出，有一个变量 ( time_bnds) 没有水平坐标变量，这是传递给的 Dataset 中的每个数据变量metpy.interpolate.cross_section所必需的（如文档中所示）。因此，我们必须在以cross_section某种方式使用之前排除此类数据变量。

对这种“类似坐标”的变量的简单修复，例如time_bnds将其提升为辅助坐标，如下所示：

data = xr.open_dataset('omega.nc')
data = data.metpy.parse_cf().squeeze().set_coords('time_bnds')

#####

start = (-7, 17)
end = (-28, 17)
cross = cross_section(data, start, end).set_coords(('latitude', 'longitude'))

这也是与https://github.com/Unidata/MetPy/discussions/2033相同的问题，因此请随时阅读该讨论，以获取更多关于未来如何在 MetPy 中改进这一点的信息和想法！

于 2022-02-07T20:57:38.003 回答