fix climb detection

The old algorithm didn't work; it left large amounts of "non-climb"
space before the climb. This is because we always kept the window at the
minimum length, so even a large mountain at the end of the window could
push the average above the ascension threshold and cause the whole
window to be included.

1 files changed, 16 insertions, 65 deletions

diff --git a/fietsboek/geo.py b/fietsboek/geo.py
index e7a58a9..190454b 100644
--- a/fietsboek/geo.py
+++ b/fietsboek/geo.py
@@ -197,71 +197,22 @@ class Path:
             yield current_climb
 
     def _climbs(self):
-        # Detection of climbs:
-        # We use a single pass over the track with two pointers, the "leader"
-        # and the "chaser". The chaser always points behind the leader. In a
-        # loop, one of each is always advanced:
-        #
-        # If the distance between leader and chaser is less than the minimum
-        # climb length, we advance the leader to enlarge the window. This
-        # does not constitute a climb.
-        #
-        # If the current ascension is below the ascension threshold, we advance
-        # the chaser. This moves the window to advance the search. If the
-        # ascension was above the threshold before the last advancement, we emit
-        # the climb (which is now over).
-        #
-        # If the current ascension is above the threshold, we advance the
-        # leader. This enlarges the window while constituting a climb.
-        try:
-            front = enumerate(self.points)
-            li, lead = next(front)
-            back = enumerate(self.points)
-            ci, chaser = next(back)
-        except StopIteration:
-            # Happens if there are no points
-            return
-
-        length = 0.0
-        elevation_diff = 0.0
-        climb_start = None
-
-        try:
-            while True:
-                if length < CLIMB_MIN_LENGTH:
-                    old_point = lead
-                    li, lead = next(front)
-                    length += old_point.distance(lead)
-                    elevation_diff += lead.elevation - old_point.elevation
-                    continue
-
-                ascension = elevation_diff / length
-                if ascension < CLIMB_MIN_ASCENSION:
-                    if climb_start is not None:
-                        yield (climb_start, li)
-                        climb_start = None
-                        # Skip to the end of the just emitted climb
-                        while ci != li:
-                            old_point = chaser
-                            ci, chaser = next(back)
-                            length -= old_point.distance(chaser)
-                            elevation_diff -= chaser.elevation - old_point.elevation
-                    else:
-                        old_point = chaser
-                        ci, chaser = next(back)
-                        length -= old_point.distance(chaser)
-                        elevation_diff -= chaser.elevation - old_point.elevation
-                else:
-                    if climb_start is None:
-                        climb_start = ci
-                    # See how much farther we can extend this climb
-                    old_point = lead
-                    li, lead = next(front)
-                    length += old_point.distance(lead)
-                    elevation_diff += lead.elevation - old_point.elevation
-        except StopIteration:
-            if climb_start is not None:
-                yield (climb_start, li)
+        i = 0
+
+        while i < len(self.points):
+            left = self.points[i]
+            j = i
+            length = 0.0
+            elevation_diff = 0.0
+            while j + 1 < len(self.points) and (length == 0.0 or elevation_diff / length >= CLIMB_MIN_ASCENSION):
+                length += self.points[j].distance(self.points[j + 1])
+                elevation_diff += self.points[j + 1].elevation - self.points[j].elevation
+                j += 1
+            if length >= CLIMB_MIN_LENGTH:
+                yield (i, j)
+                i = j
+            else:
+                i += 1
 
 
 def gpx_xml(