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rpole_util.py
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rpole_util.py
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"""
(c) Crown copyright 2018, the Met Office.
Demonstrate how to convert (to regular grid) and extract region from a cube in
rotated pole grid
"""
# -*- coding: utf-8 -*-
# author: Yaswant Pradhan
# date: 2018-06-11
from __future__ import print_function
import os
import iris
import numpy as np
import matplotlib.pyplot as plt
import iris.quickplot as qplt
def coord_rot2reg(rotated_lons, rotated_lats, pole_lon=177.5, pole_lat=37.5):
"""Convert coordinate values from rotated pole grid to regular grid.
Parameters
----------
rotated_lons : array_like
Longitude values in rotated pole grid.
rotated_lats : array_like
Latitude values in rotated pole grid.
pole_lon : real
The true longitude of the rotated pole in degrees.
pole_lat : real
The true latitude of the rotated pole in degrees.
"""
lons, lats = iris.analysis.cartography.unrotate_pole(
np.asarray(rotated_lons, 'float'),
np.asarray(rotated_lats, 'float'),
pole_lon, pole_lat)
return lons, lats
def coord_reg2rot(lons, lats, pole_lon=177.5, pole_lat=37.5):
"""Convert coordinate values from regular grid to rotated pole grid.
Parameters
----------
lons : array_like
Longitude values in regular grid.
lats : array_like
Latitude values in regular grid.
pole_lon : real
The true longitude of the rotated pole in degrees.
pole_lat : real
The true latitude of the rotated pole in degrees.
"""
rlon, rlat = iris.analysis.cartography.rotate_pole(
np.asarray(lons, 'float'),
np.asarray(lats, 'float'),
pole_lon, pole_lat)
return rlon, rlat
def reg_2dcube_template(latlim=None, lonlim=None, nlat=None, nlon=None):
"""Create a 2-dimensional cube template with regular grid coordinates.
Parameters
----------
latlim : sequence
bottom-left and top-right corner latitude values
lonlim : sequence
bottom-left and top-right corner longitude values
nlat : int
number of linearly spaced latitudes
nlon : int
number of linearly spaced longitudes
"""
latitude = iris.coords.DimCoord(
np.linspace(latlim[0], latlim[1], nlat),
standard_name='latitude', units='degrees',
coord_system=iris.coord_systems.GeogCS(6371229))
longitude = iris.coords.DimCoord(
np.linspace(lonlim[0], lonlim[1], nlon),
standard_name='longitude', units='degrees',
coord_system=iris.coord_systems.GeogCS(6371229))
cube = iris.cube.Cube(
np.zeros((nlat, nlon), np.float32),
dim_coords_and_dims=[(latitude, 0), (longitude, 1)])
return cube
def reg_cube_template(rot_cube, latlim=None, lonlim=None,
nlat=None, nlon=None, nlev=None):
"""Create a cube template with regular grid coordinates.
Parameters
----------
latlim : sequence
bottom-left and top-right corner latitude values
lonlim : sequence
bottom-left and top-right corner longitude values
nlev : int
number of levels (vertical/z coordinate)
nlat : int
number of linearly spaced latitudes (y coordinate)
nlon : int
number of linearly spaced longitudes (x coordinate)
"""
# get boundary information from the rotated pole grid
rlats = rot_cube.coords('grid_latitude')[0].points
rlons = rot_cube.coords('grid_longitude')[0].points
ny, nx = len(rlats), len(rlons)
# translate rotated to regular lon lat values for
# bl_: bottom-left, tl_: top-left, br_: bottom-right, tr_: top-right,
# tc_lat: top-centre latitude, bc_lat: bottom-centre latitude
bl_lon, bl_lat = coord_rot2reg(rlons.min(), rlats.min())
tl_lon, tl_lat = coord_rot2reg(rlons.min(), rlats.max())
br_lon, br_lat = coord_rot2reg(rlons.max(), rlats.min())
tr_lon, tr_lat = coord_rot2reg(rlons.max(), rlats.max())
_, tc_lat = coord_rot2reg(np.median(rlons), rlats.max())
_, bc_lat = coord_rot2reg(np.median(rlons), rlats.min())
# regular lat lon bounds that will include all data points in rotated grid
mm_lat = np.min([bl_lat, br_lat, bc_lat]), np.max([tl_lat, tr_lat, tc_lat])
mm_lon = np.min([bl_lon, tl_lon]), np.max([br_lon, tr_lon])
# update regular grid specifications
latlim = [latlim, mm_lat][latlim is None]
lonlim = [lonlim, mm_lon][lonlim is None]
nlat = [nlat, ny][nlat is None]
nlon = [nlon, nx][nlon is None]
cs = iris.coord_systems.GeogCS(6371229.0)
# get dimension coordinates
for coord in rot_cube.coords(dim_coords=True):
if coord.name() in ('model_level_number'):
nlev = [nlev, coord.shape[0]][nlev is None]
lev = iris.coords.DimCoord(
np.arange(nlev),
standard_name=coord.standard_name,
units=coord.units)
if coord.name() in ('latitude', 'grid_latitude'):
lat = iris.coords.DimCoord(
np.linspace(latlim[0], latlim[1], nlat),
# standard_name=coord.standard_name,
standard_name='latitude',
units=coord.units, coord_system=cs)
if coord.name() in ('longitude', 'grid_longitude'):
lon = iris.coords.DimCoord(
np.linspace(lonlim[0], lonlim[1], nlon),
standard_name='longitude',
units=coord.units, coord_system=cs)
dtype = rot_cube.data.dtype
if rot_cube.ndim == 2:
reg_cube = iris.cube.Cube(
np.empty((nlat, nlon), dtype),
# np.zeros((nlat, nlon), dtype),
dim_coords_and_dims=[(lat, 0), (lon, 1)])
elif rot_cube.ndim == 3:
reg_cube = iris.cube.Cube(
np.empty((nlev, nlat, nlon), dtype),
# np.zeros((nlev, nlat, nlon), dtype),
dim_coords_and_dims=[(lev, 0), (lat, 1), (lon, 2)])
else:
raise NotImplementedError(
'Multi-dimensional cube (>3) not supported at this time')
return reg_cube
def rotpol2regular(rot_cube, nearest=False,
latlim=None, lonlim=None, nlat=None, nlon=None):
"""convert a cube from rotated pole grid to regular grid.
Parameters
----------
rot_cube : instance
An instance of iris.cube.Cube or CubeList in rotated pole grid
nearest : bool
Use interpolation using nearest neighbour interpolation. Default is
Linear interpolation.
latlim : sequence
Minimum and Maximum regular latitude value of output cube. Read and
translated from the input cube if not present
lonlim : sequence
Minimum and Maximum regular longitude value of output cube. Read and
translated from the input cube if not present
nlat : int
Number of linearly spaced latitudes. If not present, then this equals
to the number of elements in the rotated pole grid_latitude
nlon : int
Number of linearly spaced longitudes. If not present, then this equals
to the number of elements in the rotated pole grid_longitude
"""
# Create a template cube with regular grid
reg_cube = reg_cube_template(
rot_cube, latlim=latlim, lonlim=lonlim, nlat=nlat, nlon=nlon)
if nearest is False:
scheme = iris.analysis.Linear(extrapolation_mode='mask')
else:
scheme = iris.analysis.Nearest(extrapolation_mode='mask')
# TODO: Remove derived coordinate altitude from cube or add orography cube
# to the cube
#
# print(dir(rot_cube.derived_coords[0]))
# rot_cube.remove_coord('altitude')
# rot_cube.remove_aux_factory(rot_cube.derived_coords[0])
# rot_cube.remove_aux_factory(rot_cube.aux_factories[0])
reg_cube = rot_cube.regrid(reg_cube, scheme)
print('ROT CUBE: ', rot_cube)
print('REG CUBE: ', reg_cube)
# Re-grid cube with specific scheme
return reg_cube
def demo_cube_conversion():
# -------------------------------------------------------------------------
# Demo: conversion and extraction from a rotated pole grid cube
# Save result as netcdf and show on map
# -------------------------------------------------------------------------
# Read a sample UKV surface air temperature data in rotated pole grid
pp_file = os.path.expandvars('$SCRATCH/test/UKV_OP_03_20180528.pp')
rot_cube = iris.load_cube(pp_file)
iris.save(
rot_cube,
os.path.expandvars('$SCRATCH/test/UKV_OP_03_20180528_rot.nc'),
zlib=True
)
coastlines_kw = dict(resolution='10m', linewidth=0.5)
# Plot the original cube
qplt.pcolormesh(rot_cube)
plt.gca().coastlines(**coastlines_kw)
plt.gca().gridlines()
plt.show()
# -------------------------------------------------------------------------
# Example 1: Extract rotated-pole subset from full domain
# Note: the cut out will be based on bottom-left and top-right corner
# therefore, the top corner longitude values may be missing at
# bottom corners
# -------------------------------------------------------------------------
rlon_lim, rlat_lim = coord_reg2rot([-6, 2], [50, 55])
sub_rot_cube = rot_cube.intersection(
grid_longitude=rlon_lim, grid_latitude=rlat_lim)
iris.save(
sub_rot_cube,
os.path.expandvars('$SCRATCH/test/UKV_OP_03_20180528_sub_rot.nc'),
zlib=True
)
qplt.pcolormesh(sub_rot_cube)
plt.gca().coastlines(**coastlines_kw)
plt.show()
# -------------------------------------------------------------------------
# Example 2: Convert the rotated-pole cube to regular cube (full domain)
# -------------------------------------------------------------------------
reg_cube = rotpol2regular(rot_cube)
iris.save(
reg_cube,
os.path.expandvars('$SCRATCH/test/UKV_OP_03_20180528_reg.nc'),
zlib=True
)
qplt.pcolormesh(reg_cube)
plt.gca().coastlines(**coastlines_kw)
plt.show()
# -------------------------------------------------------------------------
# Example 3: Convert the rotated-pole cube to regular cube
# (subset on-the-fly)
# -------------------------------------------------------------------------
sub_reg_cube = rotpol2regular(
rot_cube, latlim=[50, 55], lonlim=[-6, 2], nlat=320, nlon=512)
iris.save(
sub_reg_cube,
os.path.expandvars('$SCRATCH/test/UKV_OP_03_20180528_sub_reg.nc'),
zlib=True
)
qplt.pcolormesh(sub_reg_cube)
plt.gca().coastlines(**coastlines_kw)
plt.show()
# -------------------------------------------------------------------------
# Example 4: Convert the rotated-pole cube to regular cube
# (larger than the original domain)
# -------------------------------------------------------------------------
sub_reg_cube = rotpol2regular(
rot_cube, latlim=[48, 61], lonlim=[-14, 6], nlat=260, nlon=400)
iris.save(
sub_reg_cube,
os.path.expandvars('$SCRATCH/test/UKV_OP_03_20180528_sup_reg.nc'),
zlib=True
)
qplt.pcolormesh(sub_reg_cube)
plt.gca().coastlines(**coastlines_kw)
plt.gca().gridlines(linewidth=0.5)
plt.show()
if __name__ == '__main__':
# demo_cube_conversion()
pp_file = os.path.expandvars('$SCRATCH/test/20180607T0300Z.pp')
cube = iris.load(pp_file)
# print(cube)
reg_cub = []
if type(cube) is iris.cube.CubeList:
for cub in cube:
print(cub.name())
print(cub)
iris.save(
rotpol2regular(cub),
os.path.expandvars('$SCRATCH/test/') + cub.name() + '.nc',
zlib=True)
# reg_cub.append(rotpol2regular(cub))
# reg_cub.append(rotpol2regular(
# cub, latlim=(50, 55), lonlim=(-6, 2), nlat=333, nlon=533)
# )
# print(iris.cube.CubeList(reg_cub))
# iris.save(reg_cub, '$SCRATCH/test/UKV_OP_03_20180528_sub_rot.nc',
# zlib=True)
# reg_cube = reg_cube_template(
# latlim=(50, 55), lonlim=(-6, 2), nlev=70, nlat=333, nlon=533
# )
# scheme = iris.analysis.Linear(extrapolation_mode='mask')
# out = cube[2].regrid(reg_cube, scheme)
# iris.save(out, '$SCRATCH/test/20180607T0300Z_3d.nc', zlib=True)
# rlon_lim, rlat_lim = coord_reg2rot([-6, 2], [50, 55])
# sub_rot_cube = cube_list[0].intersection(
# grid_longitude=rlon_lim, grid_latitude=rlat_lim
# )
# iris.save(
# sub_rot_cube,
# '$SCRATCH/test/UKV_OP_03_20180528_sub_rot.nc', zlib=True
# )
# qplt.pcolormesh(sub_rot_cube)
# # plt.gca().coastlines(**coastlines_kw)
# plt.show()