[GIS] Split a line feature using nearby points

linepointqgis

I have a line shapefile and a point shapefile, and

the line has its own segments

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and its attribute table,

enter image description here

the point shapefile has points near the line above, not on it

enter image description here

and the close look,

enter image description here

Can I use QGIS or other open source tools to split this line at locations which are nearest to the points？ And after this procedure I can get the original line with more segments(because being split). For example, find the location on the line, which is the nearest to the point, and split the line at this location(star).

enter image description here

I am using QGIS 2.2 under Windows 8.1 x64.

Best Answer

I am not sure if this could be done in QGIS but you could use st_split for this if it helps. Try to make a buffer around your points and then split it where they intersect.

A same question is asked at Splitting line at point positions using QGIS?

Related Solutions

[GIS] Using ST_split to split a line feature using nearby points

As has been suggested earlier and in the ST_Split documentation, you must first snap your line to the points and then call ST_Split.

If you are like me, an example is worth more than words:

DROP TABLE IF EXISTS split;
CREATE TABLE split AS(
SELECT
    (ST_Dump(ST_Split(ST_Snap(a.the_geom, b.the_geom, 0.00001),b.the_geom))).geom
FROM 
    line_table a
JOIN 
    point_table b 
ON 
    ST_DWithin(b.the_geom, a.wkb_geometry, "Your Tolerance to Search for Lines (e.g., a number)")
);

[GIS] Write a python function to split polyline shapefile with point shapefile

In your first example, the problem is the cut function expects a shapely LineString object and you passed it a shapefile object.

For the second part of your question, the following example takes a point shapefile with one or more points, and cuts a line shapefile using those points. The line shapefile can be as complex as you want:

import os
import shapefile
from shapely.geometry import *

def cut(line_file, point_file, cut_file):
    """Cuts a line shapefile using a point shapefile."""
    # Line shapefile we are going to cut
    line_sf = shapefile.Reader(line_file)

    # Point shapefile containing the cut points
    point_sf = shapefile.Reader(point_file)

    # Prefix for output shapefile file name
    cut_fn = cut_file

    # Create the shapefile writer for the output line shapefile
    cut_sf = shapefile.Writer(shapefile.POLYLINE)

    cut_sf.fields = list(line_sf.fields)

    for sr in line_sf.shapeRecords():
        line = LineString(sr.shape.points)
        envelope = box(*line.bounds)
        pt = None
        for shape in point_sf.shapes():
            pt2 = Point(*shape.points[0])
            if envelope.contains(pt2):
                if not pt:
                    pt = pt2
                    continue
                if line.distance(pt2) < line.distance(pt):
                    pt = pt2
        cut_line = None
        if not pt:
            cut_line = [line]
        else:
            coords = list(line.coords)
            distance = line.project(pt)
            if distance <= 0.0 or distance >= line.length:
                return [LineString(line)]
            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:])]
        for part in cut_line:
            coords = list(part.coords)
            cut_sf.line([coords])
            cut_sf.record(*sr.record)

    cut_sf.save("{}.shp".format(cut_fn))

    # If the line shapefile has a cry file, copy it for the new file.
    shp_name = os.path.splitext(line_sf.shp.name)[0]
    line_prj = "{}.prj".format(shp_name)
    if os.path.exists(line_prj):
        with open(line_prj, "r") as line_crs:
            crs = line_crs.read()
            with open("{}.prj".format(cut_fn), "w") as cut_crs:
                cut_crs.write(crs)

# Call the function with some shapefile names        
cut("river", "points", "cut")

Best Answer

Related Solutions

[GIS] Using ST_split to split a line feature using nearby points

[GIS] Write a python function to split polyline shapefile with point shapefile

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