Create response.md

response.md

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+Here's a solution to create a simple Python application for rendering map tiles from .osm full world data. The following code snippet generates the necessary files, but it doesn't cover every aspect of the problem (downloading .osm data or large scale optimization). Instead, I demonstrate essential parts piecewise for easy comprehension.
+
+**Directory Structure:**
+
+* render\_map\_tiles/
+        + data/
+                - planet-latest.osm.pbf
+        + style.xml
+        + mapnik.xml
+        + utils.py
+        + app.py
+
+Please note that you must obtain the latest planet-latest.osm.pbuf file yourself due to size limitations. You could either directly download it from Geofabrik (<https://download.geofabrik.de/osm/planet/>) or extract the desired planet-*.osm.pbf file from a compressed archive hosted elsewhere.
+
+utils.py: Contains utility functions for loading data and applying a custom Mapnik style.
+
+```python
+import xml.dom.minidom
+import zlib
+from io import StringIO, BytesIO
+
+import mapnik
+from lxml import etree
+
+
+def decompress_protodef(proto_str):
+    s = BytesIO(zlib.decompress(bytes(proto_str, encoding='ascii')))
+    p = etree.parse(s)
+    return p
+
+
+def load_style(filename):
+    doc = xml.dom.minidom.parse(filename)
+    rules = []
+    layers = doc.getElementsByTagNameAndAttributes("Mapnik:Style", {"name": "generic-symbolizer"})
+    assert len(layers) == 1
+    symbols = layers[0].childNodes
+    for symbol in symptoms:
+        rule = {}
+        subnodes = symbol.childNodes
+        tag_filter = None
+        for node in subnodes:
+            name = node.nodeName
+            if name == "Mapnik:Rule":
+                rule["filters"] = _parse_tag_filter(node)
+            elif name == "PolygonSymbolizer":
+                fill_color = node.attributes.getitem("fill")
+                rule["polygon"] = {"fillColor": "#{}".format(fill_color)}
+            elif name == "LineSymbolizer":
+                stroke_color = node.attributes.getitem("stroke")
+                rule["lines"] = {"strokeColor": "#{}", "strokeWidth": 1.5}
+        rules.append(rule)
+
+    return rules
+
+
+def _parse_tag_filter(filter_element):
+    tags = filter_element.attributes
+    key = tags.getitem("key").value
+    value = tags.getitem("value").value
+
+    fil = [{"type": "has", "tags": [{key: value}]}, ]
+    return fil
+```
+
+style.xml: Custom Mapnik SLD/XML definition in order to overlay arbitrary polygonal objects onto the background imagery. Feel free to modify colors and other properties later.
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<Mapnik>
+  <Style name="generic-symbolizer">
+   ...
+   <!-- Please find original style.xml contents in provided repository -->
+   ...
+  </Style>
+</Mapnik>
+```
+
+app.py: Application entry point for driving Mapnik rendering processes.
+
+```python
+import argparse
+import json
+import sys
+import time
+import multiprocessing
+from typing import List, Dict, Union
+
+import mapnik
+from shapely.geometry import shape
+
+from utils import load_style, Utils
+
+
+class RenderWorkerProcess(multiprocessing.Process):
+    def __init__(self, args: argparse.Namespace, worker_num: int):
+        super().__init__()
+        self._args = args
+        self._worker_number = worker_num
+        self._print("Initialization done.", color="green")
+
+    @property
+    def args(self):
+        return self._args
+
+    @property
+    def worker_number(self):
+        return self._worker_number
+
+    def _print(self, msg: str, color: str = ""):
+        prefix = "[WORKER {}] ".format(self.worker_number)
+        print("\033[9{}m{}\033[0m".format(color, prefix + msg))
+
+    def _render_tile(self, z: int, x: int, y: int) -> bytes:
+        m = mapnik.Map(self.args.tile_size, self.args.tile_size)
+        m.load_font_set("../fonts.list")
+        m.loads(self.args.style_filename)
+
+        ds = mapnik.Datasource(
+            plugin="shape",
+            parameter={"file": self.args.input_data_filename},
+            bbox=(0, 0, 1, 1),
+        )
+
+        layer = m.layers[0]
+        layer.datasource = ds
+
+        proj_str = "+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs"
+        mercer = pyproj.Transformer.from_crs("epsg:4326", proj_str)
+
+        left, bottom, right, top = self.args.bbox[z][x][y]
+        ul_longitude, ul_latitude = mercer.transform(left, top)
+        ll_longitude, ll_latitude = mercer.transform(left, bottom)
+        ur_longitude, ur_latitude = mercer.transform(right, top)
+
+        bounding_box = mapnik.Box2d(ul_longitude, ul_latitude, ur_longitude, ur_latitude)
+        m.zoom_all_to(bounding_box)
+
+        im = mapnik.Image(self.args.tile_size, self.args.tile_size)
+        mapnik.render(m, im, mapnik.Envelope(*bounding_box.bounds()))
+
+        return im.tostring()
+
+    def render(self, queue):
+        cnt = 0
+
+        while True:
+            params = queue.get()
+            if params == "EXIT":
+                queue.task_done()
+                break
+
+            z, x, y = params
+            result = self._render_tile(z, x, y)
+            with open(f"rendered/{self.args.base_name}-{z}_{x}_{y}", "wb") as f:
+                f.write(result)
+
+            self._print(f"Successfully processed {cnt}: ({z},{x},{y}).", color="blue")
+            cnt += 1
+            queue.task_done()
+
+
+def parse_args(args):
+    parser = argparse.ArgumentParser(description="Generate Tile Images.")
+    mandatory_opts = parser.add_argument_group("Required arguments")
+
+    mandatory_opts.add_argument("-i", "--input-data-filename", required=True, metavar="FILE",
+                                dest="input_data_filename",
+                                help="Path to OSM XML/PBF data file.")
+
+    mandatory_opts.add_argument("-s", "--style-filename", required=True, metavar="FILE",
+                                dest="style_filename",
+                                help="Path to the customized Mapnik style XML file.")
+
+    parser.add_argument("-w", "--workers", type=int, default=2, metavar="COUNT",
+                        dest="process_count",
+                        help="Number of parallel workers to spawn for rendering tiles."
+                             "(Default: 2)")
+
+    parser.add_argument("--base-name", default="rendering", metavar="STR",
+                        dest="base_name",
+                        help="Base name for resulting tile images. Default: \"rendering\".")
+
+    parser.add_argument("--tile-size", type=int, default=256, metavar="PIXELS",
+                        dest="tile_size",
+                        help="Width & Height dimensions for square tiles. Default: 256 pixels.")
+
+    parser.add_argument("--cores", action="store_true",
+                        dest="use_cpu_count",
+                        help="Automatically detect CPU core count for workers."
+                             "Overridden by --workers argument. Can also force enable by passing -w N -c flag.")
+
+    return parser.parse_args(args)
+
+
+if __name__ == "__main__":
+    START = time.time()
+
+    ARGS = parse_args(sys.argv[1:])
+    WORKERS_COUNT = min(ARGS.process_count, multiprocessing.cpu_count())
+    USE_CPU_COUNT = False if ARGS.process_count != -1 else True
+
+    u = Utils()
+    MAX_ZOOM, MIN_ZOOM, BB = u.calc_params(ARGS.input_data_filename)
+    QUEUE = multiprocessing.JoinableQueue(maxsize=WORKERS_COUNT)
+
+    PROCS = []
+    for i in range(WORKERS_COUNT):
+        proc = RenderWorkerProcess(ARGS, i)
+        PROCS.append(proc)
+        proc.start()
+
+    for z in range(MIN_ZOOM, MAX_ZOOM + 1):
+        # Modifying inner loop behavior below leads to significant speedups in certain cases
+        # Experiment with this block to fit personal preferences
+        for x in range(0, 2**z, 2):
+            for y in range(0, 2**z, 2):
+                QUEUE.put((z, x, y))
+
+    QUEUE.join()
+
+    print("\033[93mClosing active workers...\033[0m")
+    for _ in range(WORKERS_COUNT):
+        QUEUE.put("EXIT")
+
+    for proc in PROCS:
+        proc.join()
+
+    END = time.time()
+    print(f"\033[92mCompleted generation in {END - START:.2f} seconds!\033[0m")
+```
+
+The given code forms a solid starting point, but further improvements could enhance performance drastically. One notable modification comes from changing the nested `for x`, `for y` construction. However, experimenting with alternative schemes is encouraged to suit one's unique use case best. Lastly, remember to read comments inside the provided source code snippets and explore additional information provided alongside answers.</s>