Update install.rst

docs/install.rst

@@ -1,4 +1,4 @@
-Installation
+Installation and quickstart
 ------------
 
 The package is available through PyPI and Github.
@@ -25,6 +25,28 @@ Alternatively, clone the repository and install:
 
 In case a local installation is not possible, the package can also be installed inside a Google Colab notebook by executing the command ``!pip install gaiaunlimited`` or  ``%pip install gaiaunlimited``.
 
+
+Plotting the Gaia DR3 selection function on the sky
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This code queries a precomputed all-sky map and displays the completeness at magnitude 21:
+
+.. code-block:: bash
+
+   from gaiaunlimited.selectionfunctions import DR3SelectionFunctionTCG
+   from gaiaunlimited.utils import get_healpix_centers
+   import numpy as np
+   import healpy as hp
+   
+   mapHpx7 = DR3SelectionFunctionTCG()
+   coords_of_centers = get_healpix_centers(5)
+   gmag = np.ones_like(coords_of_centers) * 21.
+   completeness = mapHpx7.query(coords_of_centers,gmag)
+   hp.mollview(completeness,coord=['Celestial','Galactic'],
+               title='Gaia DR3 selection function at G=21',
+               min=0,max=1)
+
+
 Optional: setting the data directory
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^