add visualization module

Author: jreiberkyle

jupyter-notebooks/pixels-to-tabular-data/visual.py

@@ -0,0 +1,46 @@
+import matplotlib.pyplot as plt
+import matplotlib.colors as colors
+import numpy as np
+
+"""
+The NDVI values will range from -1 to 1. You want to use a diverging color scheme to visualize the data,
+and you want to center the colorbar at a defined midpoint. The class below allows you to normalize the colorbar.
+"""
+class MidpointNormalize(colors.Normalize):
+    """
+    Normalise the colorbar so that diverging bars work there way either side from a prescribed midpoint value)
+    e.g. im=ax1.imshow(array, norm=MidpointNormalize(midpoint=0.,vmin=-100, vmax=100))
+    Credit: Joe Kington, http://chris35wills.github.io/matplotlib_diverging_colorbar/
+    Credit: https://stackoverflow.com/a/48598564
+    """
+    def __init__(self, vmin=None, vmax=None, midpoint=None, clip=False):
+        self.midpoint = midpoint
+        colors.Normalize.__init__(self, vmin, vmax, clip)
+    
+    def __call__(self, value, clip=None):    
+        # Note that I'm ignoring clipping and other edge cases here.
+        result, is_scalar = self.process_value(value)
+        x, y = [self.vmin, self.midpoint, self.vmax], [0, 0.5, 1]
+        return np.ma.array(np.interp(value, x, y), mask=result.mask, copy=False)
+
+
+def show_ndvi(ndvi, figsize=(20, 10)):
+    fig = plt.figure(figsize=figsize)
+    ax = fig.add_subplot(111)
+
+    # diverging color scheme chosen from https://matplotlib.org/users/colormaps.html
+    cmap = plt.cm.RdYlGn 
+
+    mmin = np.nanmin(ndvi)
+    mmax = np.nanmax(ndvi)
+    mid = 0
+
+    cax = ax.imshow(ndvi, cmap=cmap, clim=(mmin, mmax),
+                    norm=MidpointNormalize(midpoint=mid,vmin=mmin, vmax=mmax))
+
+    ax.axis('off')
+    ax.set_title('Normalized Difference Vegetation Index', fontsize=18, fontweight='bold')
+
+    cbar = fig.colorbar(cax, orientation='horizontal', shrink=0.5)
+
+    plt.show()