comment readme

Author: AntSimi

README.md

@@ -45,6 +45,7 @@ h = RegularGridDataset('share/nrt_global_allsat_phy_l4_20190223_20190226.nc', 'l
 
 Plotting grid
 ```python
+from matplotlib import pyplot as plt
 fig = plt.figure(figsize=(14, 12))
 ax = fig.add_axes([.02, .51, .9, .45])
 ax.set_title('ADT (m)')
@@ -74,3 +75,59 @@ fig.savefig('share/png/filter.png')
 
 ![signal filtering](share/png/filter.png)
 
+#### Compute spectrum and spectrum ratio on some area ####
+Load data
+```python
+grid_name, lon_name, lat_name = 'share/nrt_global_allsat_phy_l4_20190223_20190226.nc', 'longitude', 'latitude'
+raw = RegularGridDataset(grid_name, lon_name, lat_name)
+filtered = RegularGridDataset(grid_name, lon_name, lat_name)
+filtered.bessel_low_filter('adt', 150, order=3)
+
+areas = dict(
+    sud_pacific=dict(llcrnrlon=188, urcrnrlon=280, llcrnrlat=-64, urcrnrlat=-7),
+    atlantic_nord=dict(llcrnrlon=290, urcrnrlon=340, llcrnrlat=19.5, urcrnrlat=43),
+    indien_sud=dict(llcrnrlon=35, urcrnrlon=110, llcrnrlat=-49, urcrnrlat=-26),
+    )
+```
+
+Compute and display spectrum
+```python
+fig = plt.figure(figsize=(10,6))
+ax = fig.add_subplot(111)
+ax.set_title('Spectrum')
+ax.set_xlabel('km')
+for name_area, area in areas.items():
+
+    lon_spec, lat_spec = raw.spectrum_lonlat('adt', area=area)
+    mappable = ax.loglog(*lat_spec, label='lat %s raw' % name_area)[0]
+    ax.loglog(*lon_spec, label='lon %s raw' % name_area, color=mappable.get_color(), linestyle='--')
+
+    lon_spec, lat_spec = filtered.spectrum_lonlat('adt', area=area)
+    mappable = plt.loglog(*lat_spec, label='lat %s high' % name_area)[0]
+    plt.loglog(*lon_spec, label='lon %s high' % name_area, color=mappable.get_color(), linestyle='--')
+
+ax.set_xscale('log')
+ax.legend()
+ax.grid()
+fig.savefig('share/png/spectrum.png')
+```
+
+![spectrum](share/png/spectrum.png)
+
+Compute and display spectrum ratio
+```python
+fig = plt.figure(figsize=(10,6))
+ax = fig.add_subplot(111)
+ax.set_title('Spectrum ratio')
+ax.set_xlabel('km')
+for name_area, area in areas.items():
+    lon_spec, lat_spec = filtered.spectrum_lonlat('adt', area=area, ref=raw)
+    mappable = ax.plot(*lat_spec, label='lat %s high' % name_area)[0]
+    ax.plot(*lon_spec, label='lon %s high' % name_area, color=mappable.get_color(), linestyle='--')
+
+ax.set_xscale('log')
+ax.legend()
+ax.grid()
+fig.savefig('share/png/spectrum_ratio.png')
+```
+![spectrum](share/png/spectrum_ratio.png)