为什么上下文无法在自动缩放模式下获取一些瓷砖？

Question

我想使用contextily将OSM层添加到我用GeoPandas绘制的地图中。但是，在自动模式(默认)中使用zoom时，我遇到了某种随机错误。

MCVE

这是一个MCVE：

df = pd.DataFrame({"key": ["A"], "lon": [3.6], "lat": [43.4]})

point = gpd.GeoDataFrame(df, geometry=gpd.points_from_xy(df.lon, df.lat), crs=4326).to_crs(crs="ESRI:102014")
circle = point.geometry.buffer(3000)

axe = point.plot(color="red")
circle.plot(alpha=0.35, color="red", ax=axe)
ctx.add_basemap(axe, zoom="auto", crs=point.crs)

不幸的是，由于瓷砖的URL不存在，所以失败了：

---------------------------------------------------------------------------
HTTPError                                 Traceback (most recent call last)
File ~/.local/lib/python3.10/site-packages/contextily/tile.py:396, in _retryer(tile_url, wait, max_retries)
    395     request = requests.get(tile_url, headers={"user-agent": USER_AGENT})
--> 396     request.raise_for_status()
    397 except requests.HTTPError:

File /usr/local/lib/python3.10/dist-packages/requests/models.py:1021, in Response.raise_for_status(self)
   1020 if http_error_msg:
-> 1021     raise HTTPError(http_error_msg, response=self)

HTTPError: 404 Client Error: Not Found for url: https://stamen-tiles-a.a.ssl.fastly.net/terrain/14/8353/5993.png

During handling of the above exception, another exception occurred:

HTTPError                                 Traceback (most recent call last)
Cell In [9], line 3
      1 axe = point.plot(color="red")
      2 circle.plot(alpha=0.35, color="red", ax=axe)
----> 3 ctx.add_basemap(axe, zoom="auto", crs=point.crs)

File ~/.local/lib/python3.10/site-packages/contextily/plotting.py:121, in add_basemap(ax, zoom, source, interpolation, attribution, attribution_size, reset_extent, crs, resampling, **extra_imshow_args)
    117     left, right, bottom, top = _reproj_bb(
    118         left, right, bottom, top, crs, {"init": "epsg:3857"}
    119     )
    120 # Download image
--> 121 image, extent = bounds2img(
    122     left, bottom, right, top, zoom=zoom, source=source, ll=False
    123 )
    124 # Warping
    125 if crs is not None:

File ~/.local/lib/python3.10/site-packages/contextily/tile.py:222, in bounds2img(w, s, e, n, zoom, source, ll, wait, max_retries)
    220 x, y, z = t.x, t.y, t.z
    221 tile_url = provider.build_url(x=x, y=y, z=z)
--> 222 image = _fetch_tile(tile_url, wait, max_retries)
    223 tiles.append(t)
    224 arrays.append(image)

File /usr/local/lib/python3.10/dist-packages/joblib/memory.py:594, in MemorizedFunc.__call__(self, *args, **kwargs)
    593 def __call__(self, *args, **kwargs):
--> 594     return self._cached_call(args, kwargs)[0]

File /usr/local/lib/python3.10/dist-packages/joblib/memory.py:537, in MemorizedFunc._cached_call(self, args, kwargs, shelving)
    534         must_call = True
    536 if must_call:
--> 537     out, metadata = self.call(*args, **kwargs)
    538     if self.mmap_mode is not None:
    539         # Memmap the output at the first call to be consistent with
    540         # later calls
    541         if self._verbose:

File /usr/local/lib/python3.10/dist-packages/joblib/memory.py:779, in MemorizedFunc.call(self, *args, **kwargs)
    777 if self._verbose > 0:
    778     print(format_call(self.func, args, kwargs))
--> 779 output = self.func(*args, **kwargs)
    780 self.store_backend.dump_item(
    781     [func_id, args_id], output, verbose=self._verbose)
    783 duration = time.time() - start_time

File ~/.local/lib/python3.10/site-packages/contextily/tile.py:252, in _fetch_tile(tile_url, wait, max_retries)
    250 @memory.cache
    251 def _fetch_tile(tile_url, wait, max_retries):
--> 252     request = _retryer(tile_url, wait, max_retries)
    253     with io.BytesIO(request.content) as image_stream:
    254         image = Image.open(image_stream).convert("RGBA")

File ~/.local/lib/python3.10/site-packages/contextily/tile.py:399, in _retryer(tile_url, wait, max_retries)
    397 except requests.HTTPError:
    398     if request.status_code == 404:
--> 399         raise requests.HTTPError(
    400             "Tile URL resulted in a 404 error. "
    401             "Double-check your tile url:\n{}".format(tile_url)
    402         )
    403     elif request.status_code == 104:
    404         if max_retries > 0:

HTTPError: Tile URL resulted in a 404 error. Double-check your tile url:
https://stamen-tiles-a.a.ssl.fastly.net/terrain/14/8353/5993.png

有趣的是，它似乎与瓷砖的细节水平有关。因为如果我选择了一个具有更复杂几何学的点，它就会起作用：

df = pd.DataFrame({"key": ["A"], "lon": [3.7], "lat": [43.8]})

或者，如果我将缩放缩小一个单位与原来的点：

ctx.add_basemap(axe, zoom=13, crs=point.crs)

它也能工作(zoom=14是使它崩溃的值)。

分析

它似乎有一些问题，一些瓷砖没有呈现或映射到一个预期的contextily生成，因此404。

问题似乎与瓷砖本身的详细程度有关，因为：

选择一个包含很多细节的瓷砖使work;

• Reducing自动缩放，手动缩放也使有效，但分辨率较低。

问题

我没有足够的洞察力来区分它是否是contextily错误，或者它是否与瓷砖提供者有关。如何在防止404错误的同时仍然使用自动缩放模式？我能用提供程序的定义做些什么吗？为什么上下文不能在自动缩放模式下获取一些瓷砖？

Answer 1

这不是contextily的问题。雄蕊地形(默认的瓷砖)没有一个均匀的覆盖，所以有些地方有很多缩放级别，而其他地方较少。你的观察也证明了这一点。因此，上下文自动计算预期的瓷砖，但不能知道这个地方没有提供它，因为其他一些地方有相同的缩放，所以tiles元数据表示允许级别14。如果使用不同的瓷砖，则相同的代码可以工作。

ctx.add_basemap(axe, zoom="auto", crs=point.crs, source=ctx.providers.OpenStreetMap.Mapnik)