6

I have a point layer and a line layer. The points are road junctions, collected using DGPS, while the lines are the connecting roads, collected through Handheld GPS in tracking mode. As a result, the lines are not actually connected to the points.

Sample Network Image

Now I want to:

  1. Remove all intermediate nodes from each line string, to make it a straight line.

  2. Snap the start & end vertex of lines to the nearest points.

I am using PostGIS 2.0.This by far what I have done:

UPDATE line
SET geom = ST_Simplify(geom, 1000);

Q. Is there any other better way to accomplish it?(Since I am using an absurd tolerance)

UPDATE line
SET geom = ST_AddPoint(
(SELECT geom FROM line WHERE id = 1),
(SELECT p.geom FROM point AS p, line AS l
    ORDER BY ST_Distance(p.geom,(SELECT ST_StartPoint(l.geom) FROM lt WHERE l.id=1)) LIMIT 1),
0)
WHERE id=1;

This will extend the line(with id=1) to the nearest point(point added at the beginning of the line).

Q. The above looks a bit complicated, is there any other efficient method/function available?

1

Since you don't need most of the data from the green lines, you could take a very simple (simplistic?) approach and make a a point file consisting of the start and end nodes of the green lines, attributed with a line ID. Then use the ST_Snap function to snap the new points to the existing intersections (red points). Then use the ST_MakeLine function to convert your snapped start/end points into your blue lines.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.