segments.py

import fiona
from shapely.geometry import shape, mapping, LineString, MultiLineString
from copy import deepcopy

def split_segments(geometry, length):
    """Split a LineString into segments

    Parameters
    ----------
    geometry : shapely geometry
    length : float

    Returns
    -------
    A MultiLineString representing the original geometry split into segments.
    Each segment is an individual part of the geometry.
    """
    # TODO: 3D distance
    # TODO: mulitlinestring input
    # TODO: better exceptions
    assert(length > 0.0)
    coords = list(geometry.coords)
    l_cur = 0.0
    x_cur, y_cur = coords[0][0:2]
    coords_new = [coords[0]]
    lines = []
    for n in range(0, len(coords)-1):
        while True:
            x_next, y_next = coords[n+1]
            if x_cur == x_next and y_cur == y_next:
                break
            dx = x_next - x_cur
            dy = y_next - y_cur
            distance = (dx**2 + dy**2)**0.5
            if distance > (length - l_cur):
                x_cur += dx * (length - l_cur) / distance
                y_cur += dy * (length - l_cur) / distance
                coords_new.append((x_cur, y_cur))
                line = LineString(coords_new)
                lines.append(line)
                coords_new = [(x_cur, y_cur)]
                l_cur = 0.0
            else:
                x_cur, y_cur = x_next, y_next
                l_cur += distance
            coords_new.append((x_cur, y_cur))
    line = LineString(coords_new)
    lines.append(line)
    return MultiLineString(lines)


with fiona.open('D:/tmp/syphons.shp', 'r') as src:
    meta = deepcopy(src.meta)
    meta['schema']['properties']['id_seg'] = 'int:10'
    meta['schema']['properties']['firstX'] = 'float:10.1'
    meta['schema']['properties']['firstY'] = 'float:10.1'
    meta['schema']['properties']['lastX'] = 'float:10.1'
    meta['schema']['properties']['lastY'] = 'float:10.1'
    meta['schema']['properties']['length'] = 'float:10.3'
    meta['schema']['properties']['chainage'] = 'float:10.3'
    with fiona.open('output.shp', 'w', **meta) as dst:
        for feature in src:
            geometry = shape(feature['geometry'])
            count = 0
            assert(isinstance(geometry, LineString))
            segments = split_segments(geometry, 50.0)
            length = 0.0
            for segment in segments:
                feature['geometry'] = mapping(segment)
                feature['properties']['id_seg'] = count + 1
                feature['properties']['firstX'] = segment.coords[0][0]
                feature['properties']['firstY'] = segment.coords[0][0]
                feature['properties']['lastX'] = segment.coords[-1][0]
                feature['properties']['lastY'] = segment.coords[-1][0]
                feature['properties']['length'] = segment.length
                feature['properties']['chainage'] = length
                dst.write(feature)
                length += segment.length
                count += 1