在与其他LineString的交点处匀称地拆分LineString [英] Shapely Split LineStrings at Intersections with other LineStrings

问题描述

我有一组LineString，这些LineString与其他LineString相交，并且我想在这些交点处将LineString分成单独的段.我有一个解决方案，但我认为这不是最好的方法.

I have a set of LineStrings which are intersected by other LineStrings and I want to split the LineString into separate segments at these intersection points. I have a solution but I don't think it's the best approach.

假设我们正在处理一个LineString:

Let's say we are dealing with one LineString:

>>> import shapely
>>> from shapely.geometry import *
>>> import geopandas as gpd
>>> 
>>> MyLine=LineString([(0,0),(5,0),(10,3)])
>>> MyLine
<shapely.geometry.linestring.LineString object at 0x1277EEB0>
>>> 

以及与该LineString相交的2行:

And 2 lines that intersect this LineString:

>>> IntersectionLines=gpd.GeoSeries([LineString([(2,1.5),(3,-.5)]), LineString([(5,.5),(7,.5)])])
>>> IntersectionLines
0    LINESTRING (2 1.5, 3 -0.5)
1     LINESTRING (5 0.5, 7 0.5)
dtype: object
>>> 

它看起来像这样:

我可以得到如下的交点:

I can get the intersection points as follows:

>>> IntPoints=MyLine.intersection(IntersectionLines.unary_union)
>>> IntPointCoords=[x.coords[:][0] for x in IntPoints]
>>> IntPointCoords
[(2.75, 0.0), (5.833333333333333, 0.5)]
>>> 

然后我提取起点和终点，并用这些点和交点创建对，这些交点将用于形成线段:

And then I get extract the start and end points and create pairs with these and the intersection points that will be used to form line segments:

>>> StartPoint=MyLine.coords[0]
>>> EndPoint=MyLine.coords[-1]
>>> SplitCoords=[StartPoint]+IntPointCoords+[EndPoint]
>>> 
>>> def pair(list):
...     for i in range(1, len(list)):
...         yield list[i-1], list[i]
... 
>>> 
>>> SplitSegments=[LineString(p) for p in pair(SplitCoords)]     
>>> SplitSegments
[<shapely.geometry.linestring.LineString object at 0x127F7A90>, <shapely.geometry.linestring.LineString object at 0x127F7570>, <shapely.geometry.linestring.LineString object at 0x127F7930>]
>>> 

>>> gpd.GeoSeries(SplitSegments)
0                      LINESTRING (0 0, 2.75 0)
1    LINESTRING (2.75 0, 5.833333333333333 0.5)
2      LINESTRING (5.833333333333333 0.5, 10 3)
dtype: object
>>> 

但是，我的方法存在一个问题，就是我知道哪个交点应该与LineString起点连接，以及哪个交点应该与LineString终点配对.如果沿线以与起点和终点相同的顺序列出交点，则此程序将起作用.我想可能会出现并非总是这样的情况吗?有没有办法将这种方法概括化?或者完全有更好的方法?

However, one issue I have with my approach is that I know which intersection point should be joined with the LineString start point and which intersection point should be paired with the LineString end point. This program works if the intersection points are listed along the line in the same order as the start and the ending point. I imagine there would be situations where this would not always be the case? Is there a way to generalize this approach or is there a better approach entirely?

推荐答案

这里是一种更通用的方法:计算所有点(线的起点和终点+您要分割的点)沿线的距离，按这些点排序，然后以正确的顺序生成线段.一起发挥作用:

Here is a more general way: calculating the distance along the line for all points (start and end point of the line + points where you want to split), sort by these points and then generate the line segments in the right order. Together in a funtion:

def cut_line_at_points(line, points):

    # First coords of line (start + end)
    coords = [line.coords[0], line.coords[-1]]

    # Add the coords from the points
    coords += [list(p.coords)[0] for p in points]

    # Calculate the distance along the line for each point
    dists = [line.project(Point(p)) for p in coords]

    # sort the coords based on the distances
    # see http://stackoverflow.com/questions/6618515/sorting-list-based-on-values-from-another-list
    coords = [p for (d, p) in sorted(zip(dists, coords))]

    # generate the Lines
    lines = [LineString([coords[i], coords[i+1]]) for i in range(len(coords)-1)]

    return lines

在您的示例中应用此功能:

Applying this function on your example:

In [13]: SplitSegments = cut_line_at_points(MyLine, IntPoints)

In [14]: gpd.GeoSeries(SplitSegments)
Out[14]:
0                      LINESTRING (0 0, 2.75 0)
1    LINESTRING (2.75 0, 5.833333333333333 0.5)
2      LINESTRING (5.833333333333333 0.5, 10 3)
dtype: object

唯一的是，这不会保留原始线的拐角(但是您在问题中的示例也不执行此操作，因此我不知道这是否是必需条件.更复杂)

The only thing is that this does not preserve the corner from your original line (but your example in the question does this neither, so I don't know if this is a requirement. It would be possible but make it a bit more complex)

更新:一个使原始行中的角保持完整的版本(我的方法是同时保留一个0/1列表，该列表指示是否要分割坐标):

Update A version that keeps the corners in the original line intact (my approach is to also keep a list of 0/1 that indicates if a coord is to be split or not):

def cut_line_at_points(line, points):

    # First coords of line
    coords = list(line.coords)

    # Keep list coords where to cut (cuts = 1)
    cuts = [0] * len(coords)
    cuts[0] = 1
    cuts[-1] = 1

    # Add the coords from the points
    coords += [list(p.coords)[0] for p in points]    
    cuts += [1] * len(points)        

    # Calculate the distance along the line for each point    
    dists = [line.project(Point(p)) for p in coords]    
​
    # sort the coords/cuts based on the distances    
    # see http://stackoverflow.com/questions/6618515/sorting-list-based-on-values-from-another-list    
    coords = [p for (d, p) in sorted(zip(dists, coords))]    
    cuts = [p for (d, p) in sorted(zip(dists, cuts))]          

    # generate the Lines    
    #lines = [LineString([coords[i], coords[i+1]]) for i in range(len(coords)-1)]    
    lines = []        

    for i in range(len(coords)-1):    
        if cuts[i] == 1:    
            # find next element in cuts == 1 starting from index i + 1   
            j = cuts.index(1, i + 1)    
            lines.append(LineString(coords[i:j+1]))            

    return lines

应用于示例:

In [3]: SplitSegments = cut_line_at_points(MyLine, IntPoints)

In [4]: gpd.GeoSeries(SplitSegments)
Out[4]:
0                           LINESTRING (0 0, 2.75 0)
1    LINESTRING (2.75 0, 5 0, 5.833333333333333 0.5)
2           LINESTRING (5.833333333333333 0.5, 10 3)
dtype: object

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