Geography bar style

doc/bar_style_geography.py

@@ -0,0 +1,34 @@
+import matplotlib.pyplot as plt
+from matplotlib_scalebar.scalebar import ScaleBar
+from osmnx import features_from_place
+from geopandas import GeoSeries
+from shapely import Point
+
+fig, ax = plt.subplots()
+ax.xaxis.set_visible(False)
+ax.yaxis.set_visible(False)
+ax.set_facecolor("ivory")
+ax.set_xlim(58.12, 58.20)
+ax.set_ylim(54.90, 54.95)
+
+place = "Ust-Katav"
+water_gdf = features_from_place(place, tags={"natural": "water"})
+forest_gdf = features_from_place(place, {"natural": ["wood", "tree", "tree_row"]})
+landuse_gdf = features_from_place(place, tags={"landuse": True})
+highway_gdf = features_from_place(place, tags={"highway": ["secondary", "tertiary"]})
+
+forest_gdf.plot(ax=ax, facecolor="palegreen")
+landuse_gdf.plot(ax=ax, facecolor="lightgray", edgecolor="gray")
+water_gdf.plot(ax=ax, facecolor="lightskyblue", edgecolor="deepskyblue")
+highway_gdf.plot(ax=ax, color="palegoldenrod", linewidth=3)
+
+points = GeoSeries([Point(58.12, 54.90), Point(59.12, 54.90)], crs=4326).to_crs(32619)
+
+scalebar = ScaleBar(
+    dx=points[0].distance(points[1]),
+    bar_style="geography",
+    length_fraction=1,
+    width_fraction=0.03,
+)
+ax.add_artist(scalebar)
+fig.savefig("bar_style_geography.png", dpi=60, bbox_inches="tight")

matplotlib_scalebar/scalebar.py

@@ -23,6 +23,7 @@
     - scalebar.box_alpha
     - scalebar.scale_loc
     - scalebar.label_loc
+    - scalebar.bar_style
 
 See the class documentation (:class:`.Scalebar`) for a description of the
 parameters.
@@ -40,6 +41,7 @@
 # Standard library modules.
 import bisect
 import warnings
+import math
 import dataclasses
 
 # Third party modules.
@@ -61,6 +63,7 @@
     AnchoredOffsetbox,
 )
 from matplotlib.patches import Rectangle
+from matplotlib.colors import to_rgba
 
 # Local modules.
 from matplotlib_scalebar.dimension import (
@@ -89,6 +92,9 @@
 _VALID_ROTATIONS = ["horizontal", "horizontal-only", "vertical", "vertical-only"]
 _validate_rotation = ValidateInStrings("rotation", _VALID_ROTATIONS, ignorecase=True)
 
+_VALID_SCALE_STYLES = ["simple", "geography"]
+_validate_bar_style = ValidateInStrings("bar_style", _VALID_SCALE_STYLES, ignorecase=True)
+
 
 def _validate_legend_loc(loc):
     rc = matplotlib.RcParams()
@@ -111,6 +117,7 @@ def _validate_legend_loc(loc):
         "scalebar.scale_loc": ["bottom", _validate_scale_loc],
         "scalebar.label_loc": ["top", _validate_label_loc],
         "scalebar.rotation": ["horizontal", _validate_rotation],
+        "scalebar.bar_style": ["simple", _validate_bar_style],
     }
 )
 
@@ -190,6 +197,7 @@ def __init__(
         box_alpha=None,
         scale_loc=None,
         label_loc=None,
+        bar_style=None,
         font_properties=None,
         label_formatter=None,
         scale_formatter=None,
@@ -291,6 +299,10 @@ def __init__(
             If ``none`` the label is not shown.
         :type label_loc: :class:`str`
 
+        :arg bar_style: style of box
+            (default: rcParams['scalebar.bar_style'] or ``simple``)
+        :type bar_style: :class:`str`
+
         :arg font_properties: font properties of the label text, specified
             either as dict or `fontconfig <http://www.fontconfig.org/>`_
             pattern (XML).
@@ -370,6 +382,7 @@ def __init__(
         self.box_alpha = box_alpha
         self.scale_loc = scale_loc
         self.label_loc = label_loc
+        self.bar_style = bar_style
         self.scale_formatter = scale_formatter
         self.font_properties = font_properties
         self.fixed_value = fixed_value
@@ -403,6 +416,76 @@ def _calculate_exact_length(self, value, units):
         newvalue = self.dimension.convert(value, units, self.units)
         return newvalue / self.dx
 
+    def _draw_simple_rect(self, rotation, length_px, width_px, color):
+        if rotation == "horizontal":
+            rec = Rectangle(
+                (0, 0),
+                length_px,
+                width_px,
+                fill=True,
+                facecolor=color,
+                edgecolor="none",
+            )
+        else:
+            rec = Rectangle(
+                (0, 0),
+                width_px,
+                length_px,
+                fill=True,
+                facecolor=color,
+                edgecolor="none",
+            )
+        return [rec]
+
+    def _draw_geography_rect(
+        self,
+        rotation,
+        length_px,
+        width_px,
+        color,
+        value,
+    ):
+        def calc_best_step(length):
+            capacity = int(math.floor(math.log10(length)))
+            step = math.pow(10, capacity)
+            if step * 2 > length:
+                step = step / 2
+            return step
+
+        step = calc_best_step(value)
+        step_px = step * length_px / value
+
+        current_color = color
+        second_color = "white"
+
+        filled_px = 0
+        rectangles = []
+        while filled_px < length_px:
+            if filled_px + step_px <= length_px:
+                rec_step_px = step_px
+            else:
+                rec_step_px = length_px - filled_px
+            if rotation == "horizontal":
+                rec_xy = (filled_px, 0)
+                rec_width = rec_step_px
+                rec_height = width_px
+            else:
+                rec_xy = (0, filled_px)
+                rec_width = width_px
+                rec_height = rec_step_px
+            rectangle = Rectangle(
+                rec_xy,
+                rec_width,
+                rec_height,
+                fill=True,
+                facecolor=current_color,
+                edgecolor=color
+            )
+            rectangles.append(rectangle)
+            current_color, second_color = second_color, current_color
+            filled_px += rec_step_px
+        return rectangles
+
     def draw(self, renderer, *args, **kwargs):
         self._info = None
 
@@ -446,6 +529,7 @@ def _get_value(attr, default):
         box_alpha = _get_value("box_alpha", 1.0)
         scale_loc = _get_value("scale_loc", "bottom").lower()
         label_loc = _get_value("label_loc", "top").lower()
+        bar_style = _get_value("bar_style", "simple")
         font_properties = self.font_properties
         fixed_value = self.fixed_value
         fixed_units = self.fixed_units or self.units
@@ -488,28 +572,20 @@ def _get_value(attr, default):
 
         width_px = abs(ylim[1] - ylim[0]) * width_fraction
 
-        # Create scale bar
-        if rotation == "horizontal":
-            scale_rect = Rectangle(
-                (0, 0),
+        if not bar_style or bar_style == "simple":
+            scale_rects = self._draw_simple_rect(rotation, length_px, width_px, color)
+        elif bar_style == "geography":
+            scale_rects = self._draw_geography_rect(
+                rotation,
                 length_px,
                 width_px,
-                fill=True,
-                facecolor=color,
-                edgecolor="none",
-            )
-        else:
-            scale_rect = Rectangle(
-                (0, 0),
-                width_px,
-                length_px,
-                fill=True,
-                facecolor=color,
-                edgecolor="none",
+                color,
+                value,
             )
 
         scale_bar_box = AuxTransformBox(ax.transData)
-        scale_bar_box.add_artist(scale_rect)
+        for rect in scale_rects:
+            scale_bar_box.add_artist(rect)
 
         # Create scale text
         if scale_loc != "none":
@@ -796,6 +872,19 @@ def set_scale_formatter(self, scale_formatter):
 
     scale_formatter = property(get_scale_formatter, set_scale_formatter)
 
+    def get_bar_style(self):
+        return self._bar_style
+
+    def set_bar_style(self, bar_style):
+        if bar_style is not None and bar_style not in _VALID_SCALE_STYLES:
+            raise ValueError(
+                f"Unknown bar_style: {bar_style}. "
+                f"Valid bar styles: {', '.join(_VALID_SCALE_STYLES)}"
+            )
+        self._bar_style = bar_style
+
+    bar_style = property(get_bar_style, set_bar_style)
+
     def get_label_formatter(self):
         warnings.warn(
             "The get_label_formatter method is deprecated. "

tests/test_scalebar.py

@@ -59,6 +59,7 @@ def test_mpl_rcParams_update():
         "scalebar.scale_loc": "bottom",
         "scalebar.label_loc": "top",
         "scalebar.rotation": "horizontal",
+        "scalebar.bar_style": "simple",
     }
     matplotlib.rcParams.update(params)
 
@@ -371,6 +372,16 @@ def test_bbox_transform(scalebar):
     assert scalebar.bbox_transform == scalebar.axes.transAxes
 
 
+@pytest.mark.parametrize("bar_style", ["simple", "geography"])
+def test_bar_style(scalebar, bar_style):
+    assert scalebar.get_bar_style() is None
+    assert scalebar.bar_style is None
+
+    scalebar.set_bar_style(bar_style)
+    assert scalebar.get_bar_style() == bar_style
+    assert scalebar.bar_style == bar_style
+
+
 def test_info():
     fig = plt.figure()
     ax = fig.add_subplot(111)