i.atcorr: fix plot_filter function in create_iwave (OSGeo#3911)

* missing import of pyplot
* fix figures not shown correctly
* fix wrong axes

imagery/i.atcorr/create_iwave.py

@@ -155,17 +155,28 @@ def interpolate_band(values, step=2.5):
 def plot_filter(values):
     """Plot wl response values and interpolated
     filter function. This is just for checking...
-    value is a 2 column numpy array
+    value is a 2-column numpy array
     function has to be used inside Spyder python environment
     """
+    import matplotlib.pyplot as plt
+
     filter_f, limits = interpolate_band(values)
 
     # removing nodata
     w = values[:, 1] >= 0
     response = values[w]
 
-    plot(response[:, 0], response[:, 1], "ro")
-    plot(arange(limits[0], limits[1], 2.5), filter_f)
+    fig = plt.figure()
+    ax1 = fig.add_subplot(2, 1, 1)
+    ax2 = fig.add_subplot(2, 1, 2)
+
+    ax1.plot(response[:, 0], response[:, 1], "ro")
+    rounded = np.arange(limits[0], limits[1], 0.0025) * 1000
+    if len(rounded) == len(filter_f):
+        ax2.plot(rounded, filter_f)
+    else:
+        ax2.plot(rounded[:-1], filter_f)
+    plt.show()
 
 
 def pretty_print(filter_f):