It can be useful to specify position along linear features such as LineStrings and MultiLineStrings with a 1-dimensional referencing system. Shapely supports linear referencing based on length or distance, evaluating the distance along a geometric object to the projection of a given point, or the point at a given distance along the object.

使用一维参照系统指定沿线性要素（如LineStrings和MultiLineStrings）得位置是很有用的。Shapely支持基于长度或距离的线性参考，计算沿几何对象到给定点的投影距离，或沿对象给定距离点的距离。

• object.interpolate(distance[, normalized=False])

Return a point at the specified distance along a linear geometric object.

返回一个沿线性几何对象的指定距离的点。

If the normalized arg is True, the distance will be interpreted as a fraction of the geometric object’s length.

如果normalized参数为True，距离将被解释为几何对象长度的一部分。

>>> ip = LineString([(0, 0), (0, 1), (1, 1)]).interpolate(1.5)
>>> ip
<POINT (0.5 1)>
>>> LineString([(0, 0), (0, 1), (1, 1)]).interpolate(0.75, normalized=True)
<POINT (0.5 1)>

• object.project(other[, normalized=False])

Returns the distance along this geometric object to a point nearest the other object.

返回沿该几何对象到最接近另一个对象的点的距离。

If the normalized arg is True, return the distance normalized to the length of the object. The project() method is the inverse of interpolate().

如果normalized参数为True，返回对象长度的标准化距离。project()方法是interpolate()的逆运算。

>>> LineString([(0, 0), (0, 1), (1, 1)]).project(ip)
1.5
>>> LineString([(0, 0), (0, 1), (1, 1)]).project(ip, normalized=True)
0.75

For example, the linear referencing methods might be used to cut lines at a specified distance.

例如，线性参考方法可能被用来按指定的距离分割线。

def cut(line, distance):
    # Cuts a line in two at a distance from its starting point
    if distance <= 0.0 or distance >= line.length:
        return [LineString(line)]
    coords = list(line.coords)
    for i, p in enumerate(coords):
        pd = line.project(Point(p))
        if pd == distance:
            return [
                LineString(coords[:i+1]),
                LineString(coords[i:])]
        if pd > distance:
            cp = line.interpolate(distance)
            return [
                LineString(coords[:i] + [(cp.x, cp.y)]),
                LineString([(cp.x, cp.y)] + coords[i:])]

>>> line = LineString([(0, 0), (1, 0), (2, 0), (3, 0), (4, 0), (5, 0)])
>>> print([list(x.coords) for x in cut(line, 1.0)])  
[[(0.0, 0.0), (1.0, 0.0)],
 [(1.0, 0.0), (2.0, 0.0), (3.0, 0.0), (4.0, 0.0), (5.0, 0.0)]]
>>> print([list(x.coords) for x in cut(line, 2.5)])  
[[(0.0, 0.0), (1.0, 0.0), (2.0, 0.0), (2.5, 0.0)],
 [(2.5, 0.0), (3.0, 0.0), (4.0, 0.0), (5.0, 0.0)]]

标签 Python-GIS, Shapely