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将每个多线链转换为仅一个linestring

发布于 2025-02-04 19:24:58 字数 495 浏览 2 评论 0原文

在此 8168547，8171738，8170616，8169920 ）是多inineString的。

我需要将每个多界线转换为一个linestring。我尝试过很多事情，但没有任何事情可以。例如，我在R中的SF软件包中尝试了st_cast。但是，它增加了行的数量（它将每个多线线转换为几个线条）。

如何仅将每个多线线转换为一个细分线？

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四叶草在未来唯美盛开 2025-02-11 19:24:58

在geopandas中，可以用：

import geopandas as gpd
gdf = gpd.read_file(filepath)
exploded = gdf.explode()

in geopandas, this can be done with explode:

import geopandas as gpd
gdf = gpd.read_file(filepath)
exploded = gdf.explode()

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◇流星雨 2025-02-11 19:24:58

正如您提到的那样，将多in子转换为线索的{sf}通过sf :: st_cast（），将是通过sf :: ST_CAST（）。

但是您的数据存在问题 - 某些流无法进入简单的线条。 linestring必须具有一个起点和一个终点 - 对于某些RCHID来说，这根本是不可能的。结果，您的某些对象最终被复制。

由于这是一个普遍的失败 - 而不是特定的故障 - 我希望该评论对地理杂物也有效，尽管我没有运行代码来验证。

我建议首先将您的对象投入到线林中，然后识别重复物并将其过滤掉。

library(sf)
library(dplyr)

streams <- st_read("tukituki_rivStrah3.shp") %>% 
  select(-length) %>% # filtering out, as length is a derived metric
  st_cast("LINESTRING")

duplicities <- streams %>% 
  st_drop_geometry() %>% 
  group_by(rchid) %>% 
  tally %>% 
  filter(n > 1) %>% 
  pull(rchid)

# this will not do...
mapview::mapview(streams[streams$rchid == duplicities[2],])

clean_streams <- streams %>% 
  filter(!rchid %in% duplicities)

The {sf} way of converting multilinestrings to linestrings would be, as you mention, via sf::st_cast().

But there is a problem with your data - some of the streams are not possible to make into simple linestrings. A linestring must have a single start and a single end point - this is simply not possible for some of your rchids. As a result some of your objects end up being duplicated.

As this is a general failure - and not a R specific one - I would expect the comment to be valid also for geopandas, although I have not ran the code to verify.

I suggest first casting your object to linestrings, then identifying duplicites and filtering them out.

library(sf)
library(dplyr)

streams <- st_read("tukituki_rivStrah3.shp") %>% 
  select(-length) %>% # filtering out, as length is a derived metric
  st_cast("LINESTRING")

duplicities <- streams %>% 
  st_drop_geometry() %>% 
  group_by(rchid) %>% 
  tally %>% 
  filter(n > 1) %>% 
  pull(rchid)

# this will not do...
mapview::mapview(streams[streams$rchid == duplicities[2],])

clean_streams <- streams %>% 
  filter(!rchid %in% duplicities)

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彡翼 2025-02-11 19:24:58

在Geopandas中，您可以合并Linesements。如果您的多轨道干净，则段的方向相同，并且对它们进行了正确的分类。您可以尝试这样的事情：（

但可能您必须首先清洁您的细分市场:)）

...
from shapely.geometry import LineString, Point
...

def multiline_to_single_line(geometry: Union[LineString, MultiLineString]) -> LineString:
  if isinstance(geometry, LineString):
      return geometry
  coords = list(map(lambda part: list(part.coords), geometry.geoms))
  flat_coords = [Point(*point) for segment in coords for point in segment]
  return LineString(flat_coords)

gdf['geometry'] = gdf['geometry'].apply(multiline_to_single_line)

In geopandas you can merge linesegments. If your multilinestring is clean, segments have the same direction and they are properly sorted. You can try something like that:

(But probably you have to clean your segments first :))

...
from shapely.geometry import LineString, Point
...

def multiline_to_single_line(geometry: Union[LineString, MultiLineString]) -> LineString:
  if isinstance(geometry, LineString):
      return geometry
  coords = list(map(lambda part: list(part.coords), geometry.geoms))
  flat_coords = [Point(*point) for segment in coords for point in segment]
  return LineString(flat_coords)

gdf['geometry'] = gdf['geometry'].apply(multiline_to_single_line)

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