Add example on how to generate data.

docs/examples.rst

@@ -8,3 +8,4 @@ Here we collect relevant examples. The list may grow over time.
    :maxdepth: 2
 
    example_1
+   example_2

examples/example_1.ipynb.license

+This file complements pymagglobal.
+
+It is licensed under CC0 1.0 (https://creativecommons.org/publicdomain/zero/1.0/)

examples/example_2.ipynb

+%% Cell type:markdown id:681fb4de tags:
+
+# Generate synthetic data
+
+%% Cell type:markdown id:7c938d6b tags:
+
+Here we briefly show how `pymagglobal` can be used to generate synthetic data. We first set up the model we want to use to generate the synthetic data:
+
+%% Cell type:code id:5380320c tags:
+
+``` python
+from pymagglobal import Model
+
+myModel = Model('CALS10k.2')
+```
+
+%% Cell type:markdown id:98302e49 tags:
+
+Next we have to generate a data distribution. We use `pymagglobal`s `get_z_at` routine, to generate `n_at` random locations, that are uniformly distributed on the sphere. Times are drawn uniformly as well.
+
+%% Cell type:code id:68d9a6d8 tags:
+
+``` python
+from pymagglobal.utils import get_z_at
+
+import numpy as np
+from matplotlib import pyplot as plt
+from cartopy import crs as ccrs
+
+# the number of artificial records
+n_at = 400
+z_at = get_z_at(n_at, random=True)
+# set the times to something arbitrary
+z_at[3] = np.random.uniform(-1000, 1900, size=n_at)
+
+# plot the records, convert co-lat to lat
+fig, ax = plt.subplots(1, 1, subplot_kw={'projection': ccrs.Mollweide()})
+ax.scatter(z_at[1], 90-z_at[0], transform=ccrs.PlateCarree())
+ax.set_global()
+ax.coastlines();
+```
+
+%% Cell type:markdown id:cbf80490 tags:
+
+Finally we can evaluate the model at the inputs, to get synthetic ''observations'' of the field
+
+%% Cell type:code id:ea10fa42 tags:
+
+``` python
+from pymagglobal.core import field
+obs = field(z_at, myModel)
+```
+
+%% Cell type:markdown id:0c28838f tags:
+
+Let's have a look at the records:
+
+%% Cell type:code id:119a535b tags:
+
+``` python
+fig, axs = plt.subplots(1, 3, subplot_kw={'projection': ccrs.Mollweide()},
+                        figsize=(15, 4))
+titles = [r'$B_N$', r'$B_E$', r'$B_Z$']
+for it in range(3):
+    axs[it].set_title(titles[it])
+    axs[it].scatter(z_at[1], 90-z_at[0], c=obs[it], transform=ccrs.PlateCarree())
+    axs[it].set_global()
+    axs[it].coastlines();
+```
+
+%% Cell type:markdown id:99e9b776 tags:
+
+Declination, inclination and intensity records are also easily generated, by using the `field` kwargs:
+
+%% Cell type:code id:8bda1baf tags:
+
+``` python
+obs_dif = field(z_at, myModel, field_type='dif')
+fig, axs = plt.subplots(1, 3, subplot_kw={'projection': ccrs.Mollweide()},
+                        figsize=(15, 4))
+titles = [r'$D$', r'$I$', r'$F$']
+for it in range(3):
+    axs[it].set_title(titles[it])
+    axs[it].scatter(z_at[1], 90-z_at[0], c=obs_dif[it], transform=ccrs.PlateCarree())
+    axs[it].set_global()
+    axs[it].coastlines();
+```

examples/example_2.ipynb.license

+This file complements pymagglobal.
+
+It is licensed under CC0 1.0 (https://creativecommons.org/publicdomain/zero/1.0/)