Adding altitude lookup for location class

Set altitude automatically from built-in map when not specified.
See pvlib#1547

Author: nicomt

pvlib/location.py

@@ -4,7 +4,7 @@
 
 # Will Holmgren, University of Arizona, 2014-2016.
 
-import os
+import pathlib
 import datetime
 
 import pandas as pd
@@ -14,6 +14,7 @@
 from pvlib import solarposition, clearsky, atmosphere, irradiance
 from pvlib.tools import _degrees_to_index
 
+
 class Location:
     """
     Location objects are convenient containers for latitude, longitude,
@@ -44,8 +45,10 @@ class Location:
         pytz.timezone objects will be converted to strings.
         ints and floats must be in hours from UTC.
 
-    altitude : float, default 0.
+    altitude : None or float, default None
         Altitude from sea level in meters.
+        If None, the altitude will be fetched from
+        :py:func:`pvlib.location.lookup_altitude`.
 
     name : None or string, default None.
         Sets the name attribute of the Location object.
@@ -55,7 +58,8 @@ class Location:
     pvlib.pvsystem.PVSystem
     """
 
-    def __init__(self, latitude, longitude, tz='UTC', altitude=0, name=None):
+    def __init__(self, latitude, longitude, tz='UTC', altitude=None,
+                 name=None):
 
         self.latitude = latitude
         self.longitude = longitude
@@ -75,6 +79,9 @@ def __init__(self, latitude, longitude, tz='UTC', altitude=0, name=None):
         else:
             raise TypeError('Invalid tz specification')
 
+        if altitude is None:
+            altitude = lookup_altitude(latitude, longitude)
+
         self.altitude = altitude
 
         self.name = name
@@ -427,8 +434,8 @@ def lookup_altitude(latitude, longitude):
 
     """
 
-    pvlib_path = os.path.dirname(os.path.abspath(__file__))
-    filepath = os.path.join(pvlib_path, 'data', 'Altitude.h5')
+    pvlib_path = pathlib.Path(__file__).parent
+    filepath = pvlib_path / 'data' / 'Altitude.h5'
 
     latitude_index = _degrees_to_index(latitude, coordinate='latitude')
     longitude_index = _degrees_to_index(longitude, coordinate='longitude')

pvlib/tests/test_location.py

@@ -12,6 +12,7 @@
 from pytz.exceptions import UnknownTimeZoneError
 
 import pvlib
+from pvlib import location
 from pvlib.location import Location, lookup_altitude
 from pvlib.solarposition import declination_spencer71
 from pvlib.solarposition import equation_of_time_spencer71
@@ -212,7 +213,7 @@ def test_get_clearsky_valueerror(times):
 def test_from_tmy_3():
     from pvlib.tests.iotools.test_tmy import TMY3_TESTFILE
     from pvlib.iotools import read_tmy3
-    data, meta = read_tmy3(TMY3_TESTFILE, map_variables=True)
+    data, meta = read_tmy3(TMY3_TESTFILE)
     loc = Location.from_tmy(meta, data)
     assert loc.name is not None
     assert loc.altitude != 0
@@ -328,21 +329,28 @@ def test_extra_kwargs():
         Location(32.2, -111, arbitrary_kwarg='value')
 
 
-def test_lookup_altitude():
-    max_alt_error = 125
-    # location name, latitude, longitude, altitude
-    test_locations = [
-        ('Tucson, USA', 32.2540, -110.9742, 724),
-        ('Lusaka, Zambia', -15.3875, 28.3228, 1253),
-        ('Tokio, Japan', 35.6762, 139.6503, 40),
-        ('Canberra, Australia', -35.2802, 149.1310, 566),
-        ('Bogota, Colombia', 4.7110, -74.0721, 2555),
-        ('Dead Sea, West Bank', 31.525849, 35.449214, -415),
-        ('New Delhi, India', 28.6139, 77.2090, 214),
-        ('Null Island,  Atlantic Ocean', 0, 0, 0),
-    ]
-
-    for name, lat, lon, expected_alt in test_locations:
-        alt_found = lookup_altitude(lat, lon)
-        assert abs(alt_found - expected_alt) < max_alt_error, \
-            f'Max error exceded for {name} - e: {expected_alt} f: {alt_found}'
+@pytest.mark.parametrize('lat,lon,expected_alt', [
+    pytest.param(32.2540, -110.9742, 724, id='Tucson, USA'),
+    pytest.param(-15.3875, 28.3228, 1253, id='Lusaka, Zambia'),
+    pytest.param(35.6762, 139.6503, 40, id='Tokyo, Japan'),
+    pytest.param(-35.2802, 149.1310, 566, id='Canberra, Australia'),
+    pytest.param(4.7110, -74.0721, 2555, id='Bogota, Colombia'),
+    pytest.param(31.525849, 35.449214, -415, id='Dead Sea, West Bank'),
+    pytest.param(28.6139, 77.2090, 214, id='New Delhi, India'),
+    pytest.param(0, 0, 0, id='Null Island,  Atlantic Ocean'),
+])
+def test_lookup_altitude(lat, lon, expected_alt):
+    alt_found = lookup_altitude(lat, lon)
+    assert alt_found == pytest.approx(expected_alt, abs=125)
+
+
+def test_location_lookup_altitude(mocker):
+    mocker.spy(location, 'lookup_altitude')
+    tus = Location(32.2, -111, 'US/Arizona', 700, 'Tucson')
+    location.lookup_altitude.assert_not_called()
+    assert tus.altitude == 700
+    location.lookup_altitude.reset_mock()
+
+    tus = Location(32.2, -111, 'US/Arizona')
+    location.lookup_altitude.assert_called_once_with(32.2, -111)
+    assert tus.altitude == location.lookup_altitude(32.2, -111)