Source code for pyart.util.sigmath

Function for mathematical, signal processing and numerical routines.


import numpy as np
from scipy import signal

[docs]def angular_texture_2d(image, N, interval): """ Compute the angular texture of an image. Uses convolutions in order to speed up texture calculation by a factor of ~50 compared to using ndimage.generic_filter. Parameters ---------- image : 2D array of floats The array containing the velocities in which to calculate texture from. N : int This is the window size for calculating texture. The texture will be calculated from an N by N window centered around the gate. interval : float The absolute value of the maximum velocity. In conversion to radial coordinates, pi will be defined to be interval and -pi will be -interval. It is recommended that interval be set to the Nyquist velocity. Returns ------- std_dev : float array Texture of the radial velocity field. """ # transform distribution from original interval to [-pi, pi] interval_max = interval interval_min = -interval half_width = (interval_max - interval_min) / 2. center = interval_min + half_width # Calculate parameters needed for angular std. dev im = (np.asarray(image) - center) / (half_width) * np.pi x = np.cos(im) y = np.sin(im) # Calculate convolution kernel = np.ones((N, N)) xs = signal.convolve2d(x, kernel, mode="same", boundary="symm") ys = signal.convolve2d(y, kernel, mode="same", boundary="symm") ns = N**2 # Calculate norm over specified window xmean = xs/ns ymean = ys/ns norm = np.sqrt(xmean**2 + ymean**2) std_dev = np.sqrt(-2 * np.log(norm)) * (half_width) / np.pi return std_dev
[docs]def rolling_window(a, window): """ Create a rolling window object for application of functions eg:, 11), 1). """ shape = a.shape[:-1] + (a.shape[-1] - window + 1, window) strides = a.strides + (a.strides[-1], ) return np.lib.stride_tricks.as_strided(a, shape=shape, strides=strides)
[docs]def texture(radar, var): """ Determine a texture field using an 11pt stdev texarray=texture(pyradarobj, field). """ fld = radar.fields[var]['data'] print(fld.shape) tex = for timestep in range(tex.shape[0]): ray =[timestep, :], 11), 1) tex[timestep, 5:-5] = ray tex[timestep, 0:4] = np.ones(4) * ray[0] tex[timestep, -5:] = np.ones(5) * ray[-1] return tex
[docs]def texture_along_ray(radar, var, wind_size=7): """ Compute field texture along ray using a user specified window size. Parameters ---------- radar : radar object The radar object where the field is. var : str Name of the field which texture has to be computed. wind_size : int, optional Optional. Size of the rolling window used. Returns ------- tex : radar field The texture of the specified field. """ half_wind = int((wind_size-1)/2) fld = radar.fields[var]['data'] tex = for timestep in range(tex.shape[0]): ray =[timestep, :], wind_size), 1) tex[timestep, half_wind:-half_wind] = ray tex[timestep, 0:half_wind] = np.ones(half_wind) * ray[0] tex[timestep, -half_wind:] = np.ones(half_wind) * ray[-1] return tex