add Line.length property and fix docstrings

narwhal/geo.py

@@ -374,8 +374,8 @@ def _solve_NEB(alpha0, alpha1, beta1, beta2):
     return alpha2, sigma2, omega2
 
 def solve_astroid(a, f, lambda12, phi1, phi2):
-    """ Used to provide an initial guess to the inverse problem by solving the
-    corresponding problem on a sphere.
+    """ Used to provide an initial guess to the inverse problem in the case of
+    nearly antipodal points.
 
     Parameters
     ----------
@@ -401,7 +401,8 @@ def solve_astroid(a, f, lambda12, phi1, phi2):
     return alpha1
 
 def solve_vicenty(a, f, lambda12, phi1, phi2):
-    """ Used to provide an initial guess in the case of nearly antipodal points.
+    """ Used to provide an initial guess to the inverse problem by solving the
+    corresponding problem on a sphere.
 
     Parameters
     ----------
@@ -496,6 +497,10 @@ class Multipoint(MultipointBase):
 class Line(MultipointBase):
     _geotype = "Line"
 
+    @property
+    def length(self):
+        return sum(self[i].distance(self[i+1]) for i in range(len(self)-1))
+
 if __name__ == "__main__":
     # Karney's Table 2 example for the forward problem
     print("Forward problem")

tests/geo_tests.py

@@ -174,6 +174,15 @@ def test_distance_equatorial(self):
         self.assertLess(abs(d - 445277.963), 1.0)       # from geod 4.8.0
         return
 
+    def test_line_length(self):
+        line = Line([(70.205, 40.283166666666666),
+                     (70.00516666666667, 40.011),
+                     (69.89966666666666, 39.86),
+                     (69.80066666666667, 39.6955),
+                     (69.33383333333333, 39.0145),
+                     (69.18316666666666, 38.79)], crs=LonLatWGS84)
+        self.assertAlmostEqual(line.length, 187650.3233, places=2)
+        return
 
 class TestGeodesy(unittest.TestCase):