Question

我正在尝试使用docs中描述的匀称cut函数将简单的线串切成10个片段：

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 [shapely.geometry.LineString(line)]
coords = list(line.coords)
for i, p in enumerate(coords):
    pd = line.project(shapely.geometry.Point(p))
    if pd == distance:
        return [
            shapely.geometry.LineString(coords[:i+1]),
            shapely.geometry.LineString(coords[i:])]
    if pd > distance:
        cp = line.interpolate(distance)
        return [
            shapely.geometry.LineString(coords[:i] + [(cp.x, cp.y)]),
            shapely.geometry.LineString([(cp.x, cp.y)] + coords[i:])]

我使用另一个函数来调用上述函数，因为cut函数仅根据插值点将一条线分为两段：

def split_linestring(linestring, split_length):
    #cuts a linestring in length/split_length number of segments
    length = linestring.length
    result_list = []
    if length>split_length:
        while length > split_length:
            two_segment_list = cut(linestring,split_length)
            length = two_segment_list[1].length
            result_list.append(two_segment_list[0])
            #print two_segment_list[0].length
            linestring = two_segment_list[1]
        result_list.append(two_segment_list[1])
    else:
        result_list.append(linestring)
    return result_list

我编写了以下小型测试来检查线串对象的输出列表及其各自的长度：

A = shapely.geometry.Point(0, 0)
B = shapely.geometry.Point(2, 0)
AB = shapely.geometry.LineString([A, B])
split_length =Decimal('0.2')
#split_length = 0.2
r = split_linestring(AB, split_length)

for item in r:
    print item.length

输出列表看起来不错，但最后一个线串的长度接近零：

0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
2.22044604925e-16

我怀疑这是四舍五入错误，但是很难追踪到哪里或原因。如何整齐地将我的行划分为10个相等的部分，并且没有尾随的接近零的线串？

浮点精度会导致Shapely插值方法出现问题

0 个答案: