CODEWITHSUNDEEP
postgresqlpostgispolygongeojsonnominatim
m_____0
m_____0

Reputation: 405

Geopoints: From Single Coordinate to Bounds on map

I try to figure out how to come from a single given coordinate (lat/lon) to the nearest bounds which enclose this coordinate on a map e.g. streets or sea. Here two examples to give you a better understanding of what I mean:

enter image description here

enter image description here

What i tried already or thought about:

  1. Setting up a Nominatim server and search for the given coordinate via the reverse-function to get the bbox and/or the geojson polygon of this coordinate. -> this only works when the given coordinate is within a POI or for example directly on a street.
  2. Writing an algorithm to walk in all 4 or 8 directions (n/e/s/w) and 'stop' when the map layer/surface changes (change = stop for this direction and mark a bounding-point)
  3. Building up an image-recognition system using TensorFlow to detect the different colors and 'draw' the polygon. Worked with TensorFlow a couple of times but this seems to be the most tricky solution to implement (but at my current understanding the most precise one)

Does someone of you have any other ideas to get a solution for this problem? Would appreciate any kind of approaches

Cheers!

Upvotes: 1

Views: 138

Answers (1)

Jim Jones
Jim Jones

Reputation: 19693

If I got your question right, you might wanna first select all polygons in which the given point is inside of using ST_Contains, and then compute the distance to this point using ST_Distance. If you ORDER BY distance and LIMIT to 1 result you'll get the nearest polygon, e.g.

Data Sample

CREATE TABLE t (gid int, geom geometry);
INSERT INTO t VALUES 
(1,'POLYGON((-4.47 54.26,-4.44 54.28,-4.41 54.24,-4.46 54.23,-4.47 54.26))'),
(2,'POLYGON((-4.48 54.25,-4.40 54.25,-4.41 54.23,-4.48 54.23,-4.48 54.25))'),
(3,'POLYGON((-4.53 54.23,-4.44 54.29,-4.38 54.22,-4.53 54.23))');

enter image description here

Query

SELECT gid,ST_AsText(geom) FROM t
WHERE ST_Contains(geom,ST_MakePoint(-4.45, 54.25))
ORDER BY ST_Distance(geom,ST_MakePoint(-4.45, 54.25))
LIMIT 1;

 gid |                               st_astext                                
-----+------------------------------------------------------------------------
   1 | POLYGON((-4.47 54.26,-4.44 54.28,-4.41 54.24,-4.46 54.23,-4.47 54.26))
(1 Zeile)

Upvotes: 1

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