Merge pull request #403 from NCAR/minmax_3

Minmax 3

Plots/Contours/NCL_minmax_3.py

@@ -0,0 +1,250 @@
+"""
+NCL_minmax_3.py
+===============
+This script illustrates the following concepts:
+   - Calculating the local minima/maxima of your data
+   - Adding text strings at local minima/maxima locations
+   - Generating dummy data using "generate_2d_array"
+   - Setting the background color for a text box
+   - Turning on the perimeter of a text box
+
+See following URLs to see the reproduced NCL plot & script:
+    - Original NCL script: https://www.ncl.ucar.edu/Applications/Scripts/minmax_3.ncl
+    - Original NCL plot: https://www.ncl.ucar.edu/Applications/Images/minmax_3_lg.png
+"""
+
+###############################################################################
+# Import packages:
+
+import numpy as np
+import xarray as xr
+import matplotlib.pyplot as plt
+
+from geocat.viz import util as gvutil
+from geocat.viz import cmaps as gvcmaps
+
+###############################################################################
+# Definition of generate_2d_array and helper functions adapted from
+# https://github.com/NCAR/pyngl/blob/develop/src/ngl/__init__.py
+
+#  Globals for random number generator for generate_2d_array
+dfran_iseq = 0
+dfran_rseq = [
+    .749, .973, .666, .804, .081, .483, .919, .903, .951, .960, .039, .269,
+    .270, .756, .222, .478, .621, .063, .550, .798, .027, .569, .149, .697,
+    .451, .738, .508, .041, .266, .249, .019, .191, .266, .625, .492, .940,
+    .508, .406, .972, .311, .757, .378, .299, .536, .619, .844, .342, .295,
+    .447, .499, .688, .193, .225, .520, .954, .749, .997, .693, .217, .273,
+    .961, .948, .902, .104, .495, .257, .524, .100, .492, .347, .981, .019,
+    .225, .806, .678, .710, .235, .600, .994, .758, .682, .373, .009, .469,
+    .203, .730, .588, .603, .213, .495, .884, .032, .185, .127, .010, .180,
+    .689, .354, .372, .429
+]
+
+
+#  Random number generator for generate_2d_array.
+def _dfran():
+    global dfran_iseq
+    global dfran_rseq
+    dfran_iseq = dfran_iseq % 100
+    r = dfran_rseq[dfran_iseq]
+    dfran_iseq = dfran_iseq + 1
+    return r
+
+
+def generate_2d_array(dims, num_low, num_high, minv, maxv, seed=0):
+    """Generates a "nice" 2D array of pseudo random data, especially for use in
+    2D graphics.
+
+    This function has the same effect as NCL generate_2d_array.
+
+    Parameters
+    ----------
+    dims : tuple, list or array, int
+        Dimensions of the two-dimensional array to be returned.
+    num_low, num_high : int
+        Integers representing the approximate minimum and maximum number of highs and lows
+        that the output array will have. They must be in the range 1 to 25.
+        If not, then they will be set to either 1 or 25.
+    minv, maxv : float
+        The exact minimum and maximum values that the output array will have.
+    iseed : int, default to 0
+        An optional argument specifying a seed for the random number generator.
+        If iseed is outside the range 0 to 99, it will be set to 0.
+
+    Returns
+    -------
+    out_array : numpy.ndarray
+        A 2D array of pseudo random data.
+    """
+
+    # Globals for random numbers
+    global dfran_iseq
+    dfran_iseq = seed
+
+    #  Dims are reversed in order to get the same results as the NCL function.
+    nx = int(dims[1])
+    ny = int(dims[0])
+    # Column-major (Fortran-style) order in memory
+    out_array = np.zeros([nx, ny], 'f')
+    tmp_array = np.zeros([3, 25], 'f')
+    fovm = 9. / float(nx)
+    fovn = 9. / float(ny)
+    # Make sure that num_low and num_high are between 1 to 25 inclusive
+    nlow = max(1, min(25, num_low))
+    nhgh = max(1, min(25, num_high))
+    ncnt = nlow + nhgh
+
+    # Fill up the temporary array
+    for k in range(num_low):
+        # lows at random locations.
+        tmp_array[0, k] = 1. + (float(nx) - 1.) * _dfran()
+        tmp_array[1, k] = 1. + (float(ny) - 1.) * _dfran()
+        tmp_array[2, k] = -1.
+    for k in range(num_low, num_low + num_high):
+        # highs at random locations.
+        tmp_array[0, k] = 1. + (float(nx) - 1.) * _dfran()
+        tmp_array[1, k] = 1. + (float(ny) - 1.) * _dfran()
+        tmp_array[2, k] = 1.
+
+    # Initialize dmin and dmax to positive and negative infinity
+    dmin = np.inf
+    dmax = -np.inf
+    # Initialize all values in out_array to average of minv and maxv
+    midpt = 0.5 * (minv + maxv)
+    out_array[:] = midpt
+
+    # Populate out_array
+    for j in range(ny):
+        for i in range(nx):
+            for k in range(ncnt):
+                tempi = fovm * (float(i + 1) - tmp_array[0, k])
+                tempj = fovn * (float(j + 1) - tmp_array[1, k])
+                temp = -(np.square(tempi) + np.square(tempj))
+                if (temp >= -20.):
+                    out_array[i,j] = out_array[i,j] + \
+                       0.5*(maxv - minv)*tmp_array[2,k]*np.exp(temp)
+            dmin = min(dmin, out_array[i, j])
+            dmax = max(dmax, out_array[i, j])
+
+    out_array = (((out_array - dmin) / (dmax - dmin)) * (maxv - minv)) + minv
+    out_array = np.transpose(out_array, [1, 0])
+
+    del tmp_array
+
+    return out_array
+
+
+###############################################################################
+# Helper function to add contour labels of local extrema with bounding boxes
+
+
+def plotLabels(coord_locations, label):
+    # Find contour value based on longitude and latitude coordinates
+    for coord in coord_locations:
+        # Note: second item of coord (lat) accesses the index for the row number,
+        # and first item of coord (lon) access the index for the column number
+        value = round(data.data[coord[1], coord[0]], 1)
+
+        txt = ax.text(coord[0],
+                      coord[1],
+                      label + str(value),
+                      fontsize=14,
+                      horizontalalignment='center',
+                      verticalalignment='center')
+        txt.set_bbox(dict(facecolor='w', edgecolor='gray', pad=2))
+
+
+###############################################################################
+# Generate dummy data
+
+nx = 100
+ny = 100
+
+data = generate_2d_array((nx, ny), 10, 10, -19., 16., 0)
+
+# Convert data into type xarray.DataArray
+data = xr.DataArray(data,
+                    dims=["lat", "lon"],
+                    coords=dict(lat=np.arange(nx), lon=np.arange(ny)))
+
+###############################################################################
+# Plot:
+
+# Generate figure (set its size (width, height) in inches)
+plt.figure(figsize=(9.5, 8))
+
+# Generate axes
+ax = plt.axes()
+
+# Set contour levels
+levels = np.arange(-20, 18.5, 2.5)
+
+# Plot data and create colorbar
+cmap = gvcmaps.BlueYellowRed
+
+# Plot filled contour and contour lines
+contours = ax.contourf(data, cmap=cmap, levels=levels)
+lines = ax.contour(contours, linewidths=0.5, linestyles='solid', colors='black')
+
+# Find local min/max extrema with GeoCAT-Viz findLocalExtrema
+# Use below command instead after PR#46 in Viz is merged
+# lmin = gvutil.findLocalExtrema(data, eType='Low', highVal=12, lowVal=-10, eps=7)
+lmin = gvutil.findLocalExtrema(data, eType='Low', highVal=12, lowVal=-10)
+lmax = gvutil.findLocalExtrema(data, eType='High', highVal=12, lowVal=-10)
+
+# Plot labels for local extrema
+plotLabels(lmin, 'L')
+plotLabels(lmax, 'H')
+
+# Add colorbar
+cbar = plt.colorbar(contours,
+                    ax=ax,
+                    orientation='vertical',
+                    shrink=0.96,
+                    pad=0.06,
+                    extendrect=True,
+                    extendfrac='auto',
+                    aspect=15,
+                    drawedges=True,
+                    ticks=levels[1:-1:])  # set colorbar levels
+
+# Set every other tick labels to be integers
+ticklabs = cbar.ax.get_yticklabels()
+[
+    ticklabs[i].set_text(ticklabs[i].get_text()[:-2])
+    for i in range(1, len(ticklabs), 2)
+]
+
+# Center align colorbar tick labels
+cbar.ax.set_yticklabels(ticklabs, ha='center')
+cbar.ax.yaxis.set_tick_params(pad=26, length=0, labelsize=16)
+
+# Use geocat.viz.util convenience function to set axes limits & tick values without calling several matplotlib functions
+gvutil.set_axes_limits_and_ticks(ax,
+                                 xlim=(0, 99),
+                                 ylim=(0, 99),
+                                 xticks=np.arange(0, 100, 20),
+                                 yticks=np.arange(0, 100, 20))
+
+# Use geocat.viz.util convenience function to add minor and major tick lines
+gvutil.add_major_minor_ticks(ax,
+                             x_minor_per_major=4,
+                             y_minor_per_major=4,
+                             labelsize=16)
+
+# Use geocat.viz.util convenience function to add titles to left and right of the plot axis.
+gvutil.set_titles_and_labels(
+    ax,
+    maintitle='Adding your own minima/maxima text strings',
+    maintitlefontsize=24)
+
+# Set different tick font sizes and padding for X and Y axis
+ax.tick_params(axis='both', pad=10)
+
+# Set axes to be square
+ax.set_aspect(aspect='equal')
+
+# Show plot
+plt.tight_layout()
+plt.show()