Render country labels

The positions are still a bit off, because they are simply calculated as
the average of all polygon coordinates. That causes a bias towards
detailed borderlines. A better way would be to calculate the center of
mass for each polygon, but that is not implemented yet.

qsomap.py

@@ -9,10 +9,7 @@ import json
 import random
 import argparse
 
-REF_LATITUDE = 49.58666
-REF_LONGITUDE = 11.01250
-# REF_LATITUDE = -30
-# REF_LONGITUDE = 90
+LABEL_MIN_FONT_SIZE = 2
 
 
 def map_azimuthal_equidistant(lat, lon, ref_lat, ref_lon, R=1):
@@ -57,14 +54,6 @@ def map_azimuthal_equidistant(lat, lon, ref_lat, ref_lon, R=1):
     return x, y
 
 
-def random_country_color():
-    h = random.random()
-    s = 0.7
-    v = 0.8
-    r, g, b = [int(255.99*x) for x in hsv_to_rgb([h, s, v])]
-    return f"#{r:02x}{g:02x}{b:02x}"
-
-
 def is_point_in_polygon(point, polygon):
     # Idea: draw an infinite line from the test point along the x axis to the
     # right. Then check how many polygon edges this line intersects. If the
@@ -203,6 +192,18 @@ def map_all_polygons(simplegeodata, ref_lat, ref_lon, map_radius):
         v['proj_coordinates'] = proj_polys
 
 
+def hsv_to_svgstr(h, s, v):
+    r, g, b = [int(255.99*x) for x in hsv_to_rgb([h, s, v])]
+    return f"#{r:02x}{g:02x}{b:02x}"
+
+
+def assign_country_colors(simplegeodata):
+    for k, v in simplegeodata.items():
+        hue = random.random()
+        v['polygon_color'] = hsv_to_svgstr(hue, 0.7, 0.8)
+        v['label_color'] = hsv_to_svgstr(hue, 0.5, 0.4)
+
+
 def svg_add_countries(doc, simplegeodata, ref_lat, ref_lon, map_radius):
     antipodal_lat = -ref_lat
     antipodal_lon = ref_lon + np.pi
@@ -211,9 +212,9 @@ def svg_add_countries(doc, simplegeodata, ref_lat, ref_lon, map_radius):
         antipodal_lon -= 2*np.pi
 
     for k, v in simplegeodata.items():
-        print(f"Exporting {k}…", file=sys.stderr)
+        print(f"Mapping {k}…", file=sys.stderr)
 
-        color = random_country_color()
+        color = v['polygon_color']
 
         group = doc.g()
 
@@ -293,6 +294,55 @@ def svg_add_maidenhead_grid(doc, ref_lat, ref_lon, map_radius):
     doc.add(group)  # Maidenhead grid
 
 
+def svg_add_country_names(doc, simplegeodata, map_radius):
+    group = doc.g()
+
+    for k, v in simplegeodata.items():
+        print(f"Labeling {k} ", end='')
+        for poly in v['proj_coordinates']:
+            x = poly[0, :]
+            y = poly[1, :]
+
+            w = np.max(x) - np.min(x)
+            h = np.max(y) - np.min(y)
+
+            # FIXME: calculate center of mass
+            center_x = np.median(x) + map_radius
+            center_y = np.median(y) + map_radius
+
+            kwargs = {
+                    'class': 'country_label',
+                    'fill': v['label_color']
+                }
+
+            # rotate text by 90 degrees if polygon is higher than wide
+            if h > w:
+                font_size = h / len(v['name'])
+                rotate = True
+            else:
+                font_size = w / len(v['name'])
+                rotate = False
+
+            if font_size < LABEL_MIN_FONT_SIZE:
+                print('.', end='', flush=True)
+                continue  # too small
+            else:
+                print('#', end='', flush=True)
+
+            kwargs['font-size'] = font_size
+
+            txt = doc.text(v['name'], (center_x, center_y),
+                           **kwargs)
+
+            if rotate:
+                txt.rotate(90, center=(center_x, center_y))
+            group.add(txt)
+
+        print()
+
+    doc.add(group)
+
+
 def svg_add_distance_azimuth_lines(doc, ref_lat, ref_lon, map_radius):
     group = doc.g()
 
@@ -388,6 +438,7 @@ def render(ref_lat, ref_lon, output_stream):
     """
 
     map_all_polygons(simplegeodata, ref_lat, ref_lon, R)
+    assign_country_colors(simplegeodata)
 
     # generate the SVG
 
@@ -418,10 +469,13 @@ def render(ref_lat, ref_lon, output_stream):
                 opacity: 0.5;
             }
 
-            .maidenhead_label {
+            .maidenhead_label, .country_label {
                 font-family: sans-serif;
                 dominant-baseline: middle;
                 text-anchor: middle;
+            }
+
+            .maidenhead_label {
                 fill: red;
                 opacity: 0.25;
             }
@@ -432,6 +486,7 @@ def render(ref_lat, ref_lon, output_stream):
                        stroke_width=1, stroke='black'))
 
     svg_add_countries(doc, simplegeodata, ref_lat, ref_lon, R)
+    svg_add_country_names(doc, simplegeodata, R)
     svg_add_maidenhead_grid(doc, ref_lat, ref_lon, R)
     svg_add_distance_azimuth_lines(doc, ref_lat, ref_lon, R)