Merge pull request #21 from hugovk/unsquash-map

Fix squashed maps

src/stravavis/plot_map.py

@@ -1,6 +1,28 @@
+from math import log, pi, tan
+
 import matplotlib.pyplot as plt
 from rich.progress import track
 
+# Dummy units
+MAP_WIDTH = 1
+MAP_HEIGHT = 1
+
+
+def convert_x(lon):
+    # Get x value
+    x = (lon + 180) * (MAP_WIDTH / 360)
+    return x
+
+
+def convert_y(lat):
+    # Convert from degrees to radians
+    lat_rad = lat * pi / 180
+
+    # Get y value
+    mercator_n = log(tan((pi / 4) + (lat_rad / 2)))
+    y = (MAP_HEIGHT / 2) + (MAP_WIDTH * mercator_n / (2 * pi))
+    return y
+
 
 def plot_map(df, lon_min=None, lon_max= None, lat_min=None, lat_max=None,
              alpha=0.3, linewidth=0.3, output_file="map.png"):
@@ -28,6 +50,11 @@ def plot_map(df, lon_min=None, lon_max= None, lat_min=None, lat_max=None,
     for activity in track(activities, "Plotting activities"):
         x = df[df['name'] == activity]['lon']
         y = df[df['name'] == activity]['lat']
+
+        # Transform to Mercator projection so maps aren't squashed away from equator
+        x = x.transform(convert_x)
+        y = y.transform(convert_y)
+
         plt.plot(x, y, color='black', alpha=alpha, linewidth=linewidth)
 
     # Update plot aesthetics