wradlib Documentation - Bitbucket

wradlib Documentation, Release 0.1.1
>>> import numpy as np
>>> sweep_times = wradlib.util.from_to("2012-10-26 00:00:00", "2012-10-27 00:00:00", 300)
>>> depths_5min = np.random.uniform(size=(len(sweep_times)-1, 360, 128))
>>> hours = wradlib.util.from_to("2012-10-26 00:00:00", "2012-10-27 00:00:00", 3600)
>>> depths_hourly= wradlib.util.aggregate_in_time(depths_5min, sweep_times, hours, func=’sum’)
Check the shape and values of your resulting array for plausibility:
>>> print depths_hourly.shape
(24, 360, 128)
>>> print depths_hourly.mean().round()
6.0
See Also:
Get more info in the library reference section Utility functions.
2.1.7 Georeferencing and projection
In order to define the horizontal and vertical position of the radar bins, we need to retrieve the corresponding 3-
dimensional coordinates in terms of latitude, longitude and altitude. This information is required e.g. if the positions
should be plotted on a map. It is also required for constructing CAPPIs. The position of a radar bin in 3-dimensional
space depends on the position of the radar device, the elevation angle of the radar beam, as well as the azimuth angle
and the range of a bin. For the sample data used above, the posiiton of the radar device is the Feldberg in Germany
(47.8744, 8.005, 1517):
>>> import numpy as np
>>> radar_location = (47.8744, 8.005, 1517) # (lat, lon, alt) in decimal degree and meters
>>> elevation = 0.5 # in degree
>>> azimuths = np.arange(0,360) # in degrees
>>> ranges = np.arange(0, 128000., 1000.) # in meters
>>> polargrid = np.meshgrid(ranges, azimuths)
>>> lat, lon, alt = wradlib.georef.polar2latlonalt(polargrid[0], polargrid[1], elevation, radar_locat
wradlib supports the projection of geographical coordinates (lat/lon) to a Cartesian reference system. Basically, you
have to provide a string which represents the projection - based on the proj.4 library. You can look up projection
strings, but for some projections, wradlib helps you to define a projection string. In the following example, the target
projection is Gauss-Krueger (zone 3):
>>> gk3 = wradlib.georef.create_projstr("gk", zone=3)
>>> x, y = wradlib.georef.project(lat, lon, gk3)
See Also:
Get more info in the library reference section Georeferencing.
2.1.8 Gridding
Assume you would like to transfer the rainfall intensity from the above example (Conversion of reflectivity into rainfall)
from polar coordinates to a Cartesian grid, or to an arbitrary set of irregular points in space (e.g. centroids of
sub-catchments). You already retrieved the Cartesian coordinates of the radar bins in the previous section (Georeferencing
and projection). Now you only need to define the target coordinates (e.g. a grid) and apply the togrid
function of the wradlib.comp module. In this example, we want our grid only to represent the South-West sector
of our radar circle on a 100 x 100 grid. First, we define the target grid coordinates (these must be an array of 100x100
rows with one coordinate pair each):
10 Chapter 2. Tutorials