Add equirectangular distance

1 files changed, 11 insertions, 5 deletions

diff --git a/hdist.py b/hdist.py
index 3f62eb3..4fc707e 100644
--- a/hdist.py
+++ b/hdist.py
@@ -2,6 +2,9 @@ from theano import tensor
 import theano
 import numpy
 
+rearth = const(6371)
+deg2rad = const(3.141592653589793 / 180)
+
 def const(v):
     if theano.config.floatX == 'float32':
         return numpy.float32(v)
@@ -9,9 +12,6 @@ def const(v):
         return numpy.float64(v)
 
 def hdist(a, b):
-    rearth = const(6371)
-    deg2rad = const(3.141592653589793 / 180)
-
     lat1 = a[:, 0] * deg2rad
     lon1 = a[:, 1] * deg2rad
     lat2 = b[:, 0] * deg2rad
@@ -27,5 +27,11 @@ def hdist(a, b):
 
     return tensor.switch(tensor.eq(hd, float('nan')), (a-b).norm(2, axis=1), hd)
 
-
-
+def erdist(a, b):
+    lat1 = a[:, 0] * deg2rad
+    lon1 = a[:, 1] * deg2rad
+    lat2 = b[:, 0] * deg2rad
+    lon2 = b[:, 1] * deg2rad
+    x = (lon2-lon1) * tensor.cos((lat1+lat2)/2)
+    y = (lat2-lat1)
+    return tensor.sqrt(tensor.sqr(x) + tensor.sqr(y)) * rearth