使用 osmnx 提取河流数据和过滤器

Question

我正在尝试绘制特定区域的河流，但我不明白为什么

osmnx

在某些地方找不到它。 我有这个代码

import osmnx as ox

Sriver = ox.graph_from_place('Providencia, Chile', 
                             # retain_all=False, 
                             # truncate_by_edge=False,
                             # simplify=True, 
                             custom_filter='["waterway"~"river"]',
                             # custom_filter='way["waterway"]'
                             )

但是失败了：

Found no graph nodes within the requested polygon

如果我从 OSM 地图查询特征，河流显然就在那里 https://www.openstreetmap.org/query?lat=-33.41919&lon=-70.61062

我应该使用其他过滤器吗？我在文档中找不到更多信息。或者，有没有办法从一个区域中提取我可以使用的所有可用过滤器？

Answer 1

如 OSMnx 文档的入门指南中所述：

在幕后，OSMnx 做了几件事来生成最好的模型。它首先创建一个 500m 缓冲的图表，然后将其截断到所需的查询区域，以确保准确的每个节点街道统计数据并减弱图表周界影响。它还简化了图拓扑，如下所述。

你说：

我正在尝试绘制特定区域的河流，但我不明白为什么 osmnx 在某些地方找不到它。

...但要更仔细地查看您得到的完整错误回溯：

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[2], line 3
      1 import osmnx as ox
----> 3 Sriver = ox.graph_from_place('Providencia, Chile', 
      4                              # retain_all=False, 
      5                              # truncate_by_edge=False,
      6                              # simplify=True, 
      7                              custom_filter='["waterway"~"river"]',
      8                              # custom_filter='way["waterway"]'
      9                              )

File ~/Dropbox/Documents/School/Projects/Code/osmnx-repos/osmnx/osmnx/graph.py:375, in graph_from_place(query, network_type, simplify, retain_all, truncate_by_edge, which_result, buffer_dist, clean_periphery, custom_filter)
    372 utils.log("Constructed place geometry polygon(s) to query API")
    374 # create graph using this polygon(s) geometry
--> 375 G = graph_from_polygon(
    376     polygon,
    377     network_type=network_type,
    378     simplify=simplify,
    379     retain_all=retain_all,
    380     truncate_by_edge=truncate_by_edge,
    381     clean_periphery=clean_periphery,
    382     custom_filter=custom_filter,
    383 )
    385 utils.log(f"graph_from_place returned graph with {len(G):,} nodes and {len(G.edges):,} edges")
    386 return G

File ~/Dropbox/Documents/School/Projects/Code/osmnx-repos/osmnx/osmnx/graph.py:492, in graph_from_polygon(polygon, network_type, simplify, retain_all, truncate_by_edge, clean_periphery, custom_filter)
    485     G_buff = simplification.simplify_graph(G_buff)
    487 # truncate graph by original polygon to return graph within polygon
    488 # caller wants. don't simplify again: this allows us to retain
    489 # intersections along the street that may now only connect 2 street
    490 # segments in the network, but in reality also connect to an
    491 # intersection just outside the polygon
--> 492 G = truncate.truncate_graph_polygon(G_buff, polygon, retain_all, truncate_by_edge)
    494 # count how many physical streets in buffered graph connect to each
    495 # intersection in un-buffered graph, to retain true counts for each
    496 # intersection, even if some of its neighbors are outside the polygon
    497 spn = stats.count_streets_per_node(G_buff, nodes=G.nodes)

File ~/Dropbox/Documents/School/Projects/Code/osmnx-repos/osmnx/osmnx/truncate.py:162, in truncate_graph_polygon(G, polygon, retain_all, truncate_by_edge, quadrat_width, min_num)
    159 if not to_keep:
    160     # no graph nodes within the polygon: can't create a graph from that
    161     msg = "Found no graph nodes within the requested polygon"
--> 162     raise ValueError(msg)
    164 # now identify all nodes whose point geometries lie outside the polygon
    165 gs_nodes_outside_poly = gs_nodes[~gs_nodes.index.isin(to_keep)]

ValueError: Found no graph nodes within the requested polygon

OSMnx is 正在寻找您正在寻找的河流。它以 500m 缓冲图的形式执行此操作，然后将其截断回您所需的研究区域。但是因为您要求 OSMnx 自动简化图拓扑，并且因为您有一个非常琐碎的空间几何作为唯一结果，所以简化步骤 删除了研究区域内的所有图节点，仅留下研究之外的几个端点但在 500m 缓冲区内。因此，在截断到您的研究区域后，它发现您的研究边界内没有剩余的图形节点。

您可以通过 1）根本不简化图，或 2）在构建图后简化图来解决此问题。两个选项的简单示例，以及正在发生的情况的说明：

import osmnx as ox

# get boundary polygon and unsimplified graph
gdf = ox.geocode_to_gdf("Providencia, Chile")
geom = gdf.iloc[0]["geometry"]
G = ox.graph_from_polygon(geom, retain_all=True, truncate_by_edge=True, simplify=False, custom_filter='["waterway"~"river"]')

# plot unsimplified graph over boundary polygon
ax = gdf.plot()
fig, ax = ox.plot_graph(G, ax=ax, node_color="r", edge_color="k")

# plot simplified graph over boundary polygon
Gs = ox.simplify_graph(G)
ax = gdf.plot()
fig, ax = ox.plot_graph(Gs, ax=ax, node_color="r", edge_color="k")