[GIS] QGIS SAGA split lines at points creates redundant lines

linestringpointqgissplitting

I have 2 projected (ESPG 2039) layers of roads and points (bus stops and junctions). I snapped the points to the roads layer and this is how it looks:

I then try yo use Saga Split lines by points to split the lines but I get redundant lines, e.g. the green and brown lines in the middle of the picture:

Some of the redundant lines are totally independent and some are part of valid lines. I tried using different epsilon values: 0, 0.001, 0.1, 1, 5 and 10.
0.1 gave the least redundant lines, but still many exist.

Is there a way to prevent the creation of these redundant lines?
Sample data (ESPG 2039) can be found here: https://www.filedropper.com/roadsandpoints

Best Answer

If you have to use the SAGA split and you don't need the data:
1. Dissolve all the lines
2. Use the split plugin

When I tried this method, I received the expected results (though with 1 extra line that is easy to delete).

EDIT: Use spatial join to retrieve the original layer attributes, if needed

Related Solutions

PostGIS: How to Split a Line by a Point Which is on the Line But Not in the LineString Itself

aha! i found the solution:

use:

ST_Line_Locate_Point(geom_way,closest_point)

to fetch the portion of the line and then can use the following to split it correctly:

ST_Line_Substring (geom_way,0,ST_Line_Locate_Point(geom_way,closest_point)) as first_half
ST_Line_Substring (geom_way,ST_Line_Locate_Point(geom_way,closest_point),1) as other_half

QGIS – Split Lines at Intersection Points

There is few resolutions of this issue, maybe there are few better ones but this two should do also:

'By hand' (in steps)

Cut every line with another line which intersects it

Create table road_1 as 
  Select 
    row_number() over() as ID,
    input.name,
    (st_dump(st_split(input.geom, blade.geom))).geom as geom
  from roads input
  join roads blade on st_intersects(input.geom, blade.geom);

Now you've got few too much lines cause every time you're splitting one line into 2 parts, so you have to delete all lines that are covering another smaller ones (Thats why ST_NODE exists)

delete from road_1 a
where exists 
  (
  select 1 from road_1 b where a.id != b.id and st_coveredby(b.geom,a.geom)
  );

Automagically

Splitting every line in point of intersection with another line is one of things you have to do to create road topology so maybe it'll be easiest to get familiar with function pgr_createTopology of PG Routing project.

This workshop could be helpfull

Best Answer

Related Solutions

PostGIS: How to Split a Line by a Point Which is on the Line But Not in the LineString Itself

QGIS – Split Lines at Intersection Points

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