Question

我还是python的新手。我需要帮助通过简单的距离计算来计算折线的长度：

    distance = sqrt( (x1 - x2)**2 + (y1 - y2)**2 )

例如我的输入csv看起来像这样。

id    x     y     sequence
1    1.5   2.5       0
1    3.2   4.9       1
1    3.6   6.6       2
1    4.4   5.0       3
2    2.0   4.5       0
2    3.5   6.0       1

我有'id'和'sequence'（行顶点的序列号）。怎么读csv文件？如果当前'id'与前一行'id'具有相同的值，则执行距离计算：sqrt（（x [i] - x [i-1]）** 2 +（y [i] - y [i -1]）** 2）。之后，按“id”分组，并将它们的“距离”值相加。

输出csv如下所示：

id    distance
 1       ?
 2       ?

提前致谢。

Answer 1

折线：

两点之间的距离以及点与折线之间的距离：

def lineMagnitude (x1, y1, x2, y2):
    lineMagnitude = math.sqrt(math.pow((x2 - x1), 2)+ math.pow((y2 - y1), 2))
    return lineMagnitude

#Calc minimum distance from a point and a line segment (i.e. consecutive vertices in a polyline).
def DistancePointLine (px, py, x1, y1, x2, y2):
    #http://local.wasp.uwa.edu.au/~pbourke/geometry/pointline/source.vba
    LineMag = lineMagnitude(x1, y1, x2, y2)

    if LineMag < 0.00000001:
        DistancePointLine = 9999
        return DistancePointLine

    u1 = (((px - x1) * (x2 - x1)) + ((py - y1) * (y2 - y1)))
    u = u1 / (LineMag * LineMag)

    if (u < 0.00001) or (u > 1):
        #// closest point does not fall within the line segment, take the shorter distance
        #// to an endpoint
        ix = lineMagnitude(px, py, x1, y1)
        iy = lineMagnitude(px, py, x2, y2)
        if ix > iy:
            DistancePointLine = iy
        else:
            DistancePointLine = ix
    else:
        # Intersecting point is on the line, use the formula
        ix = x1 + u * (x2 - x1)
        iy = y1 + u * (y2 - y1)
        DistancePointLine = lineMagnitude(px, py, ix, iy)

    return DistancePointLine

有关详细信息，请访问：http://www.maprantala.com/2010/05/16/measuring-distance-from-a-point-to-a-line-segment/

从csv计算折线的长度

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