I want to select all polygons with area more than 350 square kilometers from my initial polygons and tried ST_Area. But my polygons are in WKID: 25832 (UTM 32N) and I read that ST_Area always calculates in WGS 84 (EPSG 4326)....
I tried it like this but did not work.
DROP TABLE IF EXISTS projekt."Final_Selection";
CREATE TABLE projekt."Final_Selection" AS
SELECT (st_area/1000000), geom
FROM projekt."New_Pot" WHERE st_area>350 ;
and like this:
DROP TABLE IF EXISTS projekt."Final_Selection";
CREATE TABLE projekt."Final_Selection" AS
SELECT (st_area(ST_Transform(geom,25832)))/10000000, geom
FROM projekt."New_Pot" WHERE st_area>350;
Does anyone have an advice for me? Thx in advance!
If you want to select geometries by their size in sqm use ST_Area with geography instead of geometry:
For geography types by default area is determined on a spheroid with units in square meters.
SELECT * FROM projekt."New_Pot"
WHERE ST_Area(ST_Transform(geom,4326)::geography) >= 350000
Note: keep in mind that using ST_Area in the WHERE clause might slow down your query significantly, as the area is being calculated in query time. If it isn't a one time query, consider creating an index with the area pre-calculated, e.g.
CREATE INDEX idx_geom ON projekt."New_Pot" (ST_Area(ST_Transform(geom,4326)::geography));
See also: Calculate the percentage of polygon inside the buffer in postgresql
In case you want to query polygons within a given radius: the easiest way would be to convert your geometry column to geography and from there use ST_DWithin, which will calculate the distance in metres when used with geography parameters:
SELECT * FROM projekt."New_Pot"
WHERE
ST_DWithin(
ST_Transform(geom,4326)::geography, -- your geometry converted to geography
ST_MakePoint(1,52)::geography, -- a given point
350000) -- a 350km buffer
Related post: Getting all Buildings in range of 5 miles from specified coordinates
Related
I have a Postgres table with some data created by using a shapefile. I need to find all records which intersect within 2 miles radius from a given latitude and longitude. I used some queries including the following one.
SELECT * FROM us_census_zcta WHERE ST_INTERSECTS(geom,
CIRCLE(POINT(40.730610, -73.935242), 2));
But none of them worked. What I am doing wrong here? How can I get the results I need?
The SRID is 4269 (NAD 83).
EDIT: After Mike Organek pointed me out that I have switched the lat-long in the above query. And then I tried a few things and the following query gave me 1 record.
SELECT * FROM us_census_zcta WHERE ST_INTERSECTS(geom::geometry,
ST_SETSRID(ST_POINT(-73.935242, 40.730610), 4269)::geometry);
But how can I use Circle and find records which intersect within 2 miles radius from that given lat-long?
What you're looking for is ST_DWithin, which will check if records intersect within a given buffer. In order to use it with miles you better cast the geometry column to geography, as it then computes distances in metres:
For geography: units are in meters and distance measurement defaults to use_spheroid=true. For faster evaluation use use_spheroid=false to measure on the sphere.
SELECT * FROM us_census_zcta
WHERE
ST_DWithin(
geom::geography,
ST_SetSRID(ST_MakePoint(-73.935242, 40.730610), 4269)::geography,
3218.688); -- ~2 miles
Keep in mind that this cast might affect query performance if the indexes aren't set properly.
See also: Getting all Buildings in range of 5 miles from specified coordinates
I have a db structure that is vanilla Postgres:
CREATE TABLE IF NOT EXISTS locations (
name text NOT NULL,
lat double precision NOT NULL,
lng double precision NOT NULL,
);
CREATE INDEX ON locations(lat,lng);
When I want to calculate all locations in a bounding box where I have the lower left and upper right corners I use the following query:
SELECT * FROM locations
WHERE lat >= min_lat AND
WHERE lat <= max_lat AND
WHERE lng >= min_lng AND
WHERE lng <= max_lng;
Now, I want to generate a bounding box given a point and use the bounding box result in the locations query. I'm using the following PostGIS query to generate a bounding box:
SELECT
ST_Extent(
ST_Envelope(
ST_Rotate(
ST_Buffer(
ST_GeomFromText('POINT (-87.6297982 41.8781136)',4326)::GEOGRAPHY,160934)::GEOMETRY,0)));
Result: BOX(-89.568160053866 40.4285062983089,-85.6903925527536 43.3273499289221)
However, I'm not sure how use the results from the PostGIS query bounding box into the vanilla lat / lng Postgres query in one call. Any ideas on how to merge the two? Preferably such that the index is preserved.
If you want to get the bbox coordinates as separated values you might wanna take a look at ST_XMax, ST_YMax, ST_XMin, ST_YMin. The following CTE, that embeds your query, should give you an idea:
WITH j (geom) AS (
SELECT
ST_Extent(ST_Envelope(
ST_Rotate(ST_Buffer(
ST_GeomFromText('POINT(-87.6297982 41.8781136)',4326)::GEOGRAPHY,160934)::GEOMETRY,0)))
)
SELECT
ST_XMax(geom),ST_YMax(geom),
ST_XMin(geom),ST_YMin(geom)
FROM j
st_xmax | st_ymax | st_xmin | st_ymin
-------------------+-----------------+-------------------+------------------
-85.6903925527536 | 43.327349928921 | -89.5681600538661 | 40.4285062983098
Side note: Storing geometry values as numbers might look straightforward but it is hardly ever the better choice - specially when dealing with polygons! So I would really suggest you to store these values as geometry or geography, which might seem complex at first a glance but definitely pays off on the long run.
This answer might shed a light on distance/containment queries involving polygons: Getting all Buildings in range of 5 miles from specified coordinates
I have a polygons table in Postgres (using PostGIS extension) named polygon having two fields (geom, id).
If I want to query the id of the polygon which intersects with the geometry of input geo-coordinate then I can do it with the below query.
SELECT id, geom
FROM polygon
WHERE ST_Intersects(polygon.%s, ST_GeometryFromText(POINT(latitude logitude), 4326));
But now I have a use case where I am getting a lot of geo-coordinates in request(~60k), now I am breaking this into lists of 1k Geo-coordinate each and querying the id of the polygon intersecting with each geo-coordinate.
I am struggling with how to write. a query for this, or if anyone has a better solution for this please suggest.
Keep in mind that the right order of coordinate pairs is lon, lat, so creating a point with lat, lon in your query will return wrong results. Your query also misses the single quotes ' around the WKT coordinate, e.g. 'POINT(1 2)'.
That all being said, you could simply paginate your result sets using ORDER BY, LIMIT and OFFSET, e.g.
Getting the first 1000 records
SELECT id, geom FROM polygon
WHERE ST_Intersects(geom, 'SRID=4326;POINT(1 2)')
ORDER BY id
LIMIT 1000 OFFSET 0;
By changing the OFFSET value you are able to retrieve the next pages.
LIMIT 1000 OFFSET 1000;
and so on ..
LIMIT 1000 OFFSET 2000;
EDIT: One way to apply this query using multiple input points is to use a CTE / subquery (see comments), e.g.
WITH j(g) AS (
VALUES
('SRID=4326;POINT(1 1)'),
('SRID=4326;POINT(1 2)')
-- ... add as many geometries as you want
)
SELECT id, geom FROM polygon, j
WHERE ST_Intersects(geom, g::geometry)
I am trying to develop a query in Postgis, where it can solve this problem:
I have a geometry and I wanna know which of the polygons that touches it, there is the highest contact area of this geometry. After I recognize this polygon I will take its value in a specific column and put this value in the same column but in my geometry.
Someone know how can I do that? I am a new user in postgresql/postgis.
As pointed out by #JGH in the comments, the overlapping area will be zero if you use ST_Touches alone. What you can do is to filter out only the geometries that do touch your reference geometry and then use ST_Intersection to get the intersection area, so that you can finally calculate the length of the intersection with ST_Length.
Data Sample
The geometry values depicted above are inside the CTE:
WITH j (id,geom) AS (
VALUES
(1,'POLYGON((-4.64 54.19,-4.59 54.19,-4.59 54.17,-4.64 54.17,-4.64 54.19))'),
(2,'POLYGON((-4.59 54.19,-4.56 54.19,-4.56 54.17,-4.59 54.17,-4.59 54.19))'),
(3,'LINESTRING(-4.65 54.19,-4.57 54.21)'),
(4,'POLYGON((-4.66 54.21,-4.60 54.21,-4.60 54.20,-4.66 54.20,-4.66 54.21))'),
(5,'POINT(-4.57 54.20)')
)
SELECT
id,
ST_Length(
ST_Intersection(
geom,
'POLYGON((-4.62 54.22,-4.58 54.22,-4.58 54.19,
-4.62 54.19,-4.62 54.22))')) AS touch_length
FROM j
WHERE
ST_Touches(
geom,
'POLYGON((-4.62 54.22,-4.58 54.22,-4.58 54.19,
-4.62 54.19,-4.62 54.22))')
ORDER BY touch_length DESC
LIMIT 1;
id | touch_length
----+---------------------
1 | 0.03000000000000025
(1 Zeile)
I have 2 tables User_places where I can see for each user their home location defined by 2 separate attributes: longitude and latitude.
And I have second table Neighborhoods with attribute 'Area', that defines each neighborhood as polygon - jsonb format - "[{"latitude":XXXXX,"longitude":YYYYY},{"latitude":ZZZZZ,"longitude":AAAAA},{"latitude":BBBBBB,"longitude":CCCCC},{"latitude":DDDDD,"longitude":EEEEE}]".
Does anybody know how to check whether particular user lives in given neighborhood in Postgresql?
SELECT
user_id,
ST_Contains(
ST_GeomFromText(
(select
replace(replace(replace(replace(replace(area::text,']','))'),'[','POLYGON(('),'}', ''),',"longitude":',' '),'{"latitude":','')
from neighbourhoods
limit 1), 4326)
(ST_SetSRID(ST_MakePoint(latitude, longitude),4326))
) as polygon_check
from user_places
I will assume you have Postgis installed on your copy of postgresql? As this has all the Geometry and geographical function extensions to postgresql.
You could use ST_Contains to check if a point is contained in a given polygon, this returns a boolean.
select ST_Contains(neigbourhood.polygon,User_place.geom)
If you don't have a geom point value in the User_places table then this can be created using the ST_SetSRID function and ST_MakePoint function.
For example - SELECT ST_SetSRID(ST_MakePoint(LAT, LON),SRID);
where SRID is the reference for the projection you are using for example 4326 for WGS 84 `
I would recommend in postgresql make sure all of your Geographical tables have geoms in them, as it makes comparisons much easier.
For reference a good place to get answers for geographic and geometry database based questions is https://gis.stackexchange.com/