pygrib学习 | 易学教程

pygrib-2.0.3/docs/index.html

导入pygrib模块

>>> import pygrib

打开grib文件，获取grib消息迭代器

>>> grbs = pygrib.open('sampledata/flux.grb')

和打开正常的python文件对象一样，pygrib使用seek, tell, read, readline, 和close方法打开grib文件。唯一的不同的是，偏移量用grib消息衡量，而不是用字节。

>>> grbs.seek(2)
  >>> grbs.tell()
  2
  >>> grb = grbs.read(1)[0] # read returns a list with the next N (N=1 in this case) messages.
  >>> grb # printing a grib message object displays summary info
  3:Maximum temperature:K (instant):regular_gg:heightAboveGround:level 2 m:fcst time 108-120 hrs:from 200402291200
  >>> grbs.tell()
  3

输出文件清单：

>>> grbs.seek(0)
  >>> for grb in grbs:
  >>>     grb 
  1:Precipitation rate:kg m**-2 s**-1 (avg):regular_gg:surface:level 0:fcst time 108-120 hrs (avg):from 200402291200
  2:Surface pressure:Pa (instant):regular_gg:surface:level 0:fcst time 120 hrs:from 200402291200
  3:Maximum temperature:K (instant):regular_gg:heightAboveGround:level 2 m:fcst time 108-120 hrs:from 200402291200
  4:Minimum temperature:K (instant):regular_gg:heightAboveGround:level 2 m:fcst time 108-120 hrs:from 200402291200

寻找匹配名字的第一个grib消息

>>> grb = grbs.select(name='Maximum temperature')[0]

使用'values'键提取数据值（grb.keys()将会返回一个可用键的序列）

# The data is returned as a numpy array, or if missing values or a bitmap
  # are present, a numpy masked array.  Reduced lat/lon or gaussian grid
  # data is automatically expanded to a regular grid. Details of the internal
  # representation of the grib data (such as the scanning mode) are handled
  # automatically.
  >>> maxt = grb.values # same as grb['values']
  >>> maxt.shape, maxt.min(), maxt.max()
  (94, 192) 223.7 319.9

获取网格经纬度值

>>> lats, lons = grb.latlons()
  >>> lats.shape, lats.min(), lats.max(), lons.shape, lons.min(), lons.max()
  (94, 192) -88.5419501373 88.5419501373  0.0 358.125

获取第二个消息

>>> grb = grbs.message(2) # same as grbs.seek(1); grb=grbs.readline()
  >>> grb
  2:Surface pressure:Pa (instant):regular_gg:surface:level 0:fcst time 120 hrs:from 200402291200

从北美洲子集中提取数据，得到经纬值

>>> data, lats, lons = grb.data(lat1=20,lat2=70,lon1=220,lon2=320)
  >>> data.shape, lats.min(), lats.max(), lons.min(), lons.max()
  (26, 53) 21.904439458 69.5216630593 221.25 318.75

使用存在的键（或者通过属性或者访问字典）修改值

>>> grb['forecastTime'] = 240
  >>> grb.dataDate = 20100101

得到与编码信息相关的二进制字符串

>>> msg = grb.tostring()
  >>> grbs.close() # close the grib file

将修改的信息写到新GRIB文件中

>>> grbout = open('test.grb','wb')
  >>> grbout.write(msg)
  >>> grbout.close()
  >>> pygrib.open('test.grb').readline() 
  1:Surface pressure:Pa (instant):regular_gg:surface:level 0:fcst time 240 hrs:from 201001011200
Documentation

============================================

注意！

select方法为从文件中，提取gribmessage对象的集合到一个列表的方法。得到的结果为一个列表（List对象），不能之前对其求keys属性。只能对单个gribmessage对象求属性！

可行的方法是打开这个List，对其中每一个元素（gribmessage对象）进行循环，分别求keys

gribmessage可以求values

index对象的slect方法比pygrib.open 对象的slect方法快，但只是适用于单变量场

findex = pygrib.index(fname,'level','month','day') # 获取messags索引

selected_messages = findex.select(level=lev,month=month,day=day) # “天选之消息”

注意：findex.select()括号中的关键字必须要和包含前面定义用到的所有关键字，否则会出现错误

来源：oschina

链接：https://my.oschina.net/u/4399244/blog/4463552

标签

surface

readline