STV_Intersect transform function
Spatially intersects points and polygons. The STV_Intersect transform function returns a tuple with matching point/polygon pairs. For every point, Vertica returns either one or many matching polygons.
You can improve performance when you parallelize the computation of the STV_Intersect transform function over multiple nodes. To parallelize the computation, use an OVER(PARTITION BEST) clause.
Behavior type
ImmutableSyntax
STV_Intersect ( { gid | i }, { g | x , y }
USING PARAMETERS index='index_name')
OVER() AS (pt_gid, pol_gid)
Arguments
gid | i- An integer column or integer that uniquely identifies the spatial object(s) of
gorxandy. g- A geometry or geography (WGS84) column that contains points. The g column can contain only point geometries or geographies. If the column contains a different geometry or geography type, STV_Intersect terminates with an error.
x- x-coordinate or longitude, FLOAT.
y- y-coordinate or latitude, FLOAT.
Parameters
index = 'index_name'- Name of the spatial index, of type VARCHAR.
Returns
pt_gid- Unique identifier of the point geometry or geography, of type INTEGER.
pol_gid- Unique identifier of the polygon geometry or geography, of type INTEGER.
Examples
The following examples show how you can use STV_Intersect transform.
Using two floats, return the matching point-polygon pairs.
=> CREATE TABLE pols (gid INT, geom GEOMETRY(1000));
CREATE TABLE
=> COPY pols(gid, gx filler LONG VARCHAR, geom AS ST_GeomFromText(gx)) FROM STDIN;
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>> 1|POLYGON((31 74,8 70,8 50,36 53,31 74))
>> \.
=> SELECT STV_Create_Index(gid, geom USING PARAMETERS index='my_polygons_1', overwrite=true,
max_mem_mb=256) OVER() FROM pols;
type | polygons | SRID | min_x | min_y | max_x | max_y | info
----------+----------+------+-------+-------+-------+-------+------
GEOMETRY | 1 | 0 | 8 | 50 | 36 | 74 |
(1 row)
=> SELECT STV_Intersect(56, 12.5683, 55.6761 USING PARAMETERS index = 'my_polygons_1') OVER();
pt_gid | pol_gid
--------+---------
56 | 1
(1 row)
Using a GEOMETRY column, return the matching point-polygon pairs.
=> CREATE TABLE polygons (gid int, geom GEOMETRY(700));
CREATE TABLE
=> COPY polygons (gid, gx filler LONG VARCHAR, geom AS ST_GeomFromText(gx)) FROM stdin;
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>> 10|POLYGON((5 5, 5 10, 10 10, 10 5, 5 5))
>> 11|POLYGON((0 0, 0 2, 2 2, 2 0, 0 0))
>> 12|POLYGON((1 1, 1 3, 3 3, 3 1, 1 1))
>> 14|POLYGON((-1 -1, -1 12, 12 12, 12 -1, -1 -1))
>> \.
=> SELECT STV_Create_Index(gid, geom USING PARAMETERS index='my_polygons', overwrite=true, max_mem_mb=256)
OVER() FROM polygons;
type | polygons | SRID | min_x | min_y | max_x | max_y | info
----------+----------+------+-------+-------+-------+-------+------
GEOMETRY | 4 | 0 | -1 | -1 | 12 | 12 |
(1 row)
=> CREATE TABLE points (gid INT, geom GEOMETRY(700));
CREATE TABLE
=> COPY points (gid, gx filler LONG VARCHAR, geom AS ST_GeomFromText(gx)) FROM stdin delimiter '|';
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>> 1|POINT(9 9)
>> 2|POINT(0 1)
>> 3|POINT(2.5 2.5)
>> 4|POINT(0 0)
>> 5|POINT(1 5)
>> 6|POINT(1.5 1.5)
>> \.
=> SELECT STV_Intersect(gid, geom USING PARAMETERS index='my_polygons') OVER (PARTITION BEST)
AS (point_id, polygon_gid)
FROM points;
point_id | polygon_gid
----------+-------------
5 | 14
1 | 14
1 | 10
4 | 14
4 | 11
6 | 12
6 | 14
6 | 11
2 | 14
2 | 11
3 | 12
3 | 14
(12 rows)
You can improve query performance by using the STV_Intersect transform function in a WHERE clause. Performance improves because this syntax eliminates all points that do not intersect polygons in the index.
Return the count of points that intersect with the polygon, where gid = 14:
=> SELECT COUNT(pt_id) FROM
(SELECT STV_Intersect(gid, geom USING PARAMETERS index='my_polygons')
OVER (PARTITION BEST) AS (pt_id, pol_id) FROM points)
AS T WHERE pol_id = 14;
COUNT
-------
6
(1 row)