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我對xarray中的時間變量有誤解。我有時間既是無限的維度和變量netcdf4文件這樣定義(如座標變量):python xarray失去時間變量的單位屬性
double time(time=59231);
:_Netcdf4Dimid = 0; // int
:units = "seconds since 2015-11-12 16:1:48.500000 0:00";
還有保存在文件中EPIC約定時間(因爲我還在來回在此之間約定的測試代碼)
int EPIC_time(time=59231);
:units = "True Julian Day";
:epic_code = 624; // int
:datum = "Time (UTC) in True Julian Days: 2440000 = 0000 h on May 23, 1968";
:NOTE = "Decimal Julian day [days] = time [days] + (time2 [msec]/86400000 [msec/day])";
:_Netcdf4Dimid = 0; // int
:serial_number = "23881";
:sensor_type = "TRDI";
:sensor_depth = 10.367607116699219; // double
:initial_sensor_height = 1; // int
:initial_sensor_height_note = "height in meters above bottom: accurate for tripod mounted instruments";
:height_depth_units = "m";
:_FillValue = -1; // int
:_Unsigned = "true";
而且還有與儀器標題中有太多的變量:
float Hdg_1215(time=59231, lat=1, lon=1);
:_FillValue = 1.0E35f; // float
:units = "degrees";
:name = "Hdg";
要打開文件,並用它,我做這項工作:
import xarray as xr
import numpy as np
import datetime as dt
vars2omit = {'EPIC_time','EPIC_time2'}
ds = xr.open_dataset(infile,decode_times=True,drop_variables=vars2omit)
我可以繪製和處理數據。儘管有兩個非常奇怪的行爲,其解釋將幫助我理解xarray的內部工作原理。
文件打開後,嘗試訪問時間變量(座標時間變量)的單位屬性失敗。爲什麼?該屬性在文件中。
print(ds['Hdg_1215'].attrs['units']) # this works
print(ds['time'].attrs['units']) # this fails, KeyError: 'units'