suppose you are given the co-ordinates of starting and end points of a road
segment.
Is there any way to extract the other set of co-ordinates laying on the
road segment
?
An example +++++++++++++
Here's an approach using Spatialite:
You can use the spatialite functions DissolvePoints() or DissolveSegments()
to get each point or line segment along a LINESTRING. Here's an example:
(I created in advance a sample LINESTRING called 'seg')
PRAGMA table_info("seg");
0 pk_uid integer 0 NULL 1
1 label text 0 NULL 0
2 Geometry LINESTRING 0 NULL 0
SELECT * FROM seg;
1 a BLOB sz=176 GEOMETRY
2 b BLOB sz=112 GEOMETRY
(I have two simple LINESTRINGs)
SELECT AsText(Geometry) FROM seg;
LINESTRING(1 1, 2 1, 2 2, 3 2, 4 2, 5 3, 6 2, 7 1)
LINESTRING(2 2, 2 4, 4 4, 5 2)
Now, I want to choose one of the linestrings, based on it's start and end
points:
SELECT AsText(Geometry) FROM seg
WHERE StartPoint(Geometry) = GeomFromText('POINT(1 1)', 4326) AND
EndPoint(Geometry) = GeomFromText('POINT(7 1)', 4326);
LINESTRING(1 1, 2 1, 2 2, 3 2, 4 2, 5 3, 6 2, 7 1)
and to break up the LINESTRING into its segments:
SELECT AsText(DissolveSegments(Geometry)) FROM seg
WHERE StartPoint(Geometry) = GeomFromText('POINT(1 1)', 4326) AND
EndPoint(Geometry) = GeomFromText('POINT(7 1)', 4326);
MULTILINESTRING((1 1, 2 1), (2 1, 2 2), (2 2, 3 2), (3 2, 4 2), (4 2, 5 3),
(5 3, 6 2), (6 2, 7 1))
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