Circular drawer scale (#82)

* add cli argument for circular drawer: maximum distance to scale runs to

* Fix typos, implement scaling of distances and rings

* Fix year and help text

* quantity only if argument is given

* examples for animated gifs

gpxtrackposter/circular_drawer.py

@@ -43,6 +43,7 @@ def __init__(self, the_poster: Poster) -> None:
         super().__init__(the_poster)
         self._rings = False
         self._ring_color = "darkgrey"
+        self._max_distance = None
 
     def create_args(self, args_parser: argparse.ArgumentParser) -> None:
         """Add arguments to the parser"""
@@ -61,11 +62,20 @@ def create_args(self, args_parser: argparse.ArgumentParser) -> None:
             default="darkgrey",
             help="Color of distance rings.",
         )
+        group.add_argument(
+            "--circular-ring-max-distance",
+            dest="circular_ring_max_distance",
+            metavar="DISTANCE KM",
+            type=float,
+            help="Maximum distance for scaling the track length.",
+        )
 
     def fetch_args(self, args: argparse.Namespace) -> None:
         """Get arguments from the parser"""
         self._rings = args.circular_rings
         self._ring_color = args.circular_ring_color
+        if args.circular_ring_max_distance:
+            self._max_distance = abs(args.circular_ring_max_distance) * Units().km
 
     def draw(self, dr: svgwrite.Drawing, g: svgwrite.container.Group, size: XY, offset: XY) -> None:
         """Draw the circular Poster using distances broken down by time"""
@@ -195,6 +205,8 @@ def _draw_rings(
             return
         min_length = length_range.lower()
         max_length = length_range.upper()
+        if self._max_distance:
+            max_length = self._max_distance
         assert min_length is not None
         assert max_length is not None
         ring_distance = self._determine_ring_distance(max_length)
@@ -229,6 +241,8 @@ def _draw_circle_segment(
         has_special = len([t for t in tracks if t.special]) > 0
         color = self.color(self.poster.length_range_by_date, length, has_special)
         max_length = self.poster.length_range_by_date.upper()
+        if self._max_distance:
+            max_length = self._max_distance.to_base_units()
         assert max_length is not None
         r1 = rr.lower()
         assert r1 is not None