Questions tagged [knn]
use this tag when dealing with questions related to kNN(K-Nearest Neighbors) a spatial property.
82
questions
4
votes
2
answers
95
views
Calculating accurate distances using various ST_Distance options
I want to get the nearest neighbour information for a point, and I'm getting different results based on different geometry/geography types. Assuming I only care about the most accurate result, which ...
- 695
3
votes
1
answer
87
views
PostGIS query to get the closest data available
I've got three tables in a PostgreSQL/PostGIS database:
referencia.comarcas_agrarias_centroides (holds geom centroids of agricultural regions)
referencia.estaciones_r_pen (holds geom locations of ...
- 3,230
4
votes
1
answer
99
views
Dynamically drawing the polygon formed by nearest points to @map_extent_center in QGIS
From a DEM raster layer I created a set of random points and informed each point with the value of 'ELEVATION'.
I also used the following expression to connect the 10 points closest to the @...
- 2,419
2
votes
1
answer
88
views
KNN (<->) order by -- possible to use spatial index with a secondary order by?
From reading here as well as the docs, I know how to use the <-> operator in my order by in order to do KNN search, and this is fast and uses the gist spatial index as expected. However, I have ...
3
votes
0
answers
92
views
Slow KNN within fixed radius search (PostGIS) - ST_DWITHIN vs KNN
Ask:
I want to return all customers matching certain characteristics within a 50 mile radius of the incoming zip code. This query takes just over a second to complete, and that's because of this line:
...
8
votes
1
answer
267
views
Connecting dynamically the 8 nearest lines to @map_extent_center in QGIS
Starting from a points geometry layer, I am working on the following function that has the goal of drawing 8 nearest lines to the @map_extent_center of the map view:
make_line(
$geometry,
@...
- 2,419
11
votes
2
answers
303
views
Creating buffers to closest distances with two categories in QGIS
I would like to develop an expression that does the following nearest-neighbour analysis:
From a layer of points 'point_layer', I would like to calculate for each point the distance to the nearest ...
- 2,419
2
votes
1
answer
114
views
Trying to get accurate results using ST_DWithin with srid -1
I have a table where each row has a point Geometry(POINT(...)) [long lat]. These geometries don't specify an srid. Which means we're using a cartesian plane to do the calculations. All of this data is ...
- 21
0
votes
0
answers
22
views
Using QGIS, what is the simplest way to find the closest point in one layer for every point in the second layer?
In QGIS, I have two layers of points (layer #1 - blue, and layer #2 - pink).
How can I find the closest point in layer #1 for each point in layer #2, and then save this new selection as its own new ...
- 109
1
vote
1
answer
72
views
Distance unit in KNN using cross join lateral
The underlying geometries are SRID 4326. I want to confirm whether "pma.dist" in the select clause would be a distance in meters. Here is my code:
SELECT
clusters.areaid,
...
- 857
3
votes
2
answers
123
views
Match rows from different tables by comparing similar lat lon coordinates
I am new to PostgreSQL and PostGIS. The first project I am working on is the first I am struggeling with and the one I would like to discuss.
I have 2 stops tables I call for simplicity tbl_stops_1 ...
2
votes
1
answer
216
views
Select points within a buffer / radius of a point [duplicate]
When a user click on a map, I first want to get closest point (placename), then use that point to get number of points (schools) within 10km buffer / radius
...
$str = pg_query($conn, "SELECT ...
- 83
2
votes
1
answer
138
views
Optimizing KNN query with multiple search conditions
I have two point tables in SRID 4326: Table 1. unjoined_pts & Table 2. midpts. I want to join the attributes from the unjoined_pts table to the closest midpts table based on a few conditions. The ...
- 995
6
votes
1
answer
378
views
Documentation for <->
I found this question and am wondering, is it for PostgreSQL? Where’s the documentation for <->? Trying to find the fastest way to get the distance between a lat and long earth coordinates in ...
- 161
1
vote
2
answers
512
views
Find nearest point of interest for each category in PostgreSQL
I have 2 tables: poi and categories with below schema.
POI table:
id
name
category
geog
1
poi-1
cat-1
point()
2
poi-2
cat-1
point()
3
poi-3
cat-2
point()
4
poi-4
cat-3
point()
..
..
..
..
...
- 405