Add beach_profile_elevation function

Gets elevation from an x-coordinate on a beach profile.

src/data/profile_features.py

@@ -139,6 +139,25 @@ def distance_to_intersection(lat, lon, landward_orientation, beach, line_strings
     # If no intersections are found, return nothing.
     return None
 
+
+def beach_profile_elevation(x_coord, df_profiles, profile_type, site_id):
+    """
+    Returns the beach profile elevation at a particular x-coordinate
+    :param x_coord:
+    :param df_profiles:
+    :param profile_type: "prestorm" or "poststorm"
+    :param site_id:
+    :return:
+    """
+
+    if np.isnan(x_coord):
+        return None
+
+    # Get profile
+    df_profile = df_profiles.query('profile_type == "{}" and site_id =="{}"'.format(profile_type, site_id))
+    return np.interp(x_coord, df_profile.index.get_level_values('x'), df_profile['z'])
+
+
 # todo
 def get_sites_dune_crest_toe():
     """