add layer2img.py

contours/README.md

@@ -9,6 +9,7 @@ Usage:
 3. Run `make -j$(nproc) smooth_<X>.gpkg`. This will output a geo-package with
    contour lines every `X` meters. X can be fractional (e.g.
    `smooth_2.5.gpkg`).
+4. Optional: you may generate a raster image with `layer2img.py`.
 
 Dependencies:
 

contours/layer2img.py

@@ -0,0 +1,72 @@
+#!/usr/bin/python3
+import argparse
+import geopandas
+import psycopg2
+import matplotlib.pyplot as plt
+
+INCH = 25.4  # mm
+BROWN = '#d15c00'  # CMYK: 0_56_100_18
+
+
+def plt_size(string):
+    if not string:
+        return None
+    try:
+        w, h = string.split("x")
+        return float(w) / INCH, float(h) / INCH
+    except Exception as e:
+        raise argparse.ArgumentTypeError from e
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(
+            description='Convert geopackage to an image')
+    group1 = parser.add_mutually_exclusive_group()
+    group1.add_argument('--infile')
+    group1.add_argument('--table')
+    parser.add_argument('-o', '--outfile', metavar='<file>')
+    parser.add_argument(
+            '--dpi', type=int, help='Dots per inch', default=300)
+    parser.add_argument(
+            '--size', type=plt_size, help='Figure size in mm (WWxHH)')
+
+    return parser.parse_args()
+
+
+def read_layer(maybe_table, maybe_file):
+    if maybe_table:
+        conn = psycopg2.connect("host=127.0.0.1 dbname=osm user=osm")
+        sql = "SELECT geom FROM %s" % maybe_table
+        return geopandas.read_postgis(sql, con=conn, geom_col='geom')
+    elif maybe_file:
+        return geopandas.read_file(maybe_file)
+
+
+def plot_layer(layer, ax, color):
+    layer.plot(ax=ax, color=BROWN, linewidth=.5)
+
+
+def main():
+    args = parse_args()
+    layer = read_layer(args.table, args.infile)
+
+    fig, ax = plt.subplots()
+    if args.size:
+        fig.set_size_inches(args.size)
+
+    plot_layer(layer, ax=ax, color=BROWN)
+
+    ax.axis('off')
+    ax.margins(0, 0)
+    fig.tight_layout(0)
+    if args.outfile:
+        fig.savefig(
+            args.outfile, bbox_inches=0, dpi=args.dpi,
+            pil_kwargs={'compression': 'tiff_deflate'},
+        )
+    else:
+        plt.show()
+
+
+if __name__ == '__main__':
+    main()