Plotting with pyresample and Basemap

Pyresample supports basic integration with Basemap (http://matplotlib.sourceforge.net/basemap).

Displaying data quickly

Pyresample has some convenience functions for displaying data from a single channel. The function plot.show_quicklook shows a Basemap image of a dataset for a specified AreaDefinition. The function plot.save_quicklook saves the Basemap image directly to file.

Example usage:

>>> import numpy as np
>>> import pyresample as pr
>>> lons = np.zeros(1000)
>>> lats = np.arange(-80, -90, -0.01)
>>> tb37v = np.arange(1000)
>>> area_def = pr.utils.load_area('areas.cfg', 'ease_sh')
>>> swath_def = pr.geometry.SwathDefinition(lons, lats)
>>> result = pr.kd_tree.resample_nearest(swath_def, tb37v, area_def,
...                                      radius_of_influence=20000, fill_value=None)
>>> pr.plot.save_quicklook('tb37v_quick.png', area_def, result, label='Tb 37v (K)')
Assuming lons, lats and tb37v are initialized with real data the result might look something like this:
_images/tb37v_quick.png

The data passed to the functions is a 2D array matching the AreaDefinition.

The Plate Carree projection

The Plate Carree projection (regular lon/lat grid) is named eqc in Proj.4 and cyl in Basemap. pyresample uses the Proj.4 name. Assuming the file areas.cfg has the following area definition:

REGION: pc_world {
   NAME:    Plate Carree world map
   PCS_ID:  pc_world
   PCS_DEF: proj=eqc
   XSIZE: 640
   YSIZE: 480
   AREA_EXTENT:  (-20037508.34, -10018754.17, 20037508.34, 10018754.17)
};

Example usage:

>>> import numpy as np
>>> import pyresample as pr
>>> lons = np.zeros(1000)
>>> lats = np.arange(-80, -90, -0.01)
>>> tb37v = np.arange(1000)
>>> area_def = pr.utils.load_area('areas.cfg', 'pc_world')
>>> swath_def = pr.geometry.SwathDefinition(lons, lats)
>>> result = pr.kd_tree.resample_nearest(swath_def, tb37v, area_def, radius_of_influence=20000, fill_value=None)
>>> pr.plot.save_quicklook('tb37v_pc.png', area_def, result, num_meridians=0, num_parallels=0, label='Tb 37v (K)')
Assuming lons, lats and tb37v are initialized with real data the result might look something like this:
_images/tb37v_pc.png

The Globe projections

From v0.7.12 pyresample can use the geos, ortho and nsper projections with Basemap. Assuming the file areas.cfg has the following area definition for an ortho projection area:

REGION: ortho {
  NAME:    Ortho globe
  PCS_ID:  ortho_globe
  PCS_DEF: proj=ortho, a=6370997.0, lon_0=40, lat_0=-40
  XSIZE: 640
  YSIZE: 480
  AREA_EXTENT:  (-10000000, -10000000, 10000000, 10000000)
};

Example usage:

>>> import numpy as np
>>> import pyresample as pr
>>> lons = np.zeros(1000)
>>> lats = np.arange(-80, -90, -0.01)
>>> tb37v = np.arange(1000)
>>> area_def = pr.utils.load_area('areas.cfg', 'ortho')
>>> swath_def = pr.geometry.SwathDefinition(lons, lats)
>>> result = pr.kd_tree.resample_nearest(swath_def, tb37v, area_def, radius_of_influence=20000, fill_value=None)
>>> pr.plot.save_quicklook('tb37v_ortho.png', area_def, result, num_meridians=0, num_parallels=0, label='Tb 37v (K)')
Assuming lons, lats and tb37v are initialized with real data the result might look something like this:
_images/tb37v_ortho.png

Getting a Basemap object

In order to make more advanced plots than the preconfigured quicklooks a Basemap object can be generated from an AreaDefintion using the plot.area_def2basemap(area_def, **kwargs) function.

Example usage:

>>> import numpy as np
>>> import matplotlib.pyplot as plt
>>> import pyresample as pr
>>> lons = np.zeros(1000)
>>> lats = np.arange(-80, -90, -0.01)
>>> tb37v = np.arange(1000)
>>> area_def = pr.utils.load_area('areas.cfg', 'ease_sh')
>>> swath_def = pr.geometry.SwathDefinition(lons, lats)
>>> result = pr.kd_tree.resample_nearest(swath_def, tb37v, area_def,
...                                      radius_of_influence=20000, fill_value=None)
>>> bmap = pr.plot.area_def2basemap(area_def)
>>> bmng = bmap.bluemarble()
>>> col = bmap.imshow(result, origin='upper')
>>> plt.savefig('tb37v_bmng.png', bbox_inches='tight')
Assuming lons, lats and tb37v are initialized with real data the result might look something like this:
_images/tb37v_bmng.png

Any keyword arguments (not concerning the projection) passed to plot.area_def2basemap will be passed directly to the Basemap initialization.

For more information on how to plot with Basemap please refer to the Basemap and matplotlib documentation.

Limitations

The pyresample use of Basemap is basically a conversion from a pyresample AreaDefintion to a Basemap object which allows for correct plotting of a resampled dataset using the basemap.imshow function.

Currently only the following set of Proj.4 arguments can be interpreted in the conversion: {‘proj’, ‘a’, ‘b’, ‘ellps’, ‘lon_0’, ‘lat_0’, ‘lon_1’, ‘lat_1’, ‘lon_2’, ‘lat_2’, ‘lat_ts’}

Any other Proj.4 parameters will be ignored. If the ellipsoid is not defined in terms of ‘ellps’, ‘a’ or (‘a’, ‘b’) it will default to WGS84.

The xsize and ysize in an AreaDefinition will only be used during resampling when the image data for use in basemap.imshow is created. The actual size and shape of the final plot is handled by matplotlib.