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osspatial [2015/04/17 18:07] glaroc [Exercise] |
osspatial [2015/04/20 18:06] (current) glaroc [Spatial relationships between layers] |
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- Repeat these steps to import the "ProtectedAreas-Quebec.shp", "Hydrography-Surface.shp" and | - Repeat these steps to import the "ProtectedAreas-Quebec.shp", "Hydrography-Surface.shp" and | ||
==== Basic spatial queries on single layers ==== | ==== Basic spatial queries on single layers ==== | ||
- | ST_Length | + | **sum**(expression) aggregate to return a sum for a set of records\\ |
- | ST_Area | + | **count**(expression) aggregate to return the size of a set of records\\ |
- | ST_ | + | **ST_GeometryType**(geometry) returns the type of the geometry\\ |
+ | **ST_SRID**(geometry) returns the spatial reference identifier number of the geometry\\ | ||
+ | **ST_X**(point) returns the X ordinate\\ | ||
+ | **ST_Y**(point) returns the Y ordinate\\ | ||
+ | **ST_Length**(linestring) returns the length of the linestring\\ | ||
+ | **ST_StartPoint**(geometry) returns the first coordinate as a point\\ | ||
+ | **ST_EndPoint**(geometry) returns the last coordinate as a point\\ | ||
+ | **ST_Area**(geometry) returns the area of the polygons\\ | ||
+ | **ST_Perimeter**(geometry) returns the length of all the rings\\ | ||
+ | **ST_AsSVG**(geometry) returns SVG text\\ | ||
- | Sum the area of all districts | + | Sum the area of all seas |
<file postgresql> | <file postgresql> | ||
- | SELECT tri_cep, sum(ST_Area(geom)) FROM section_vote_31h5_utm GROUP BY tri_cep | + | SELECT iho_sea, sum(ST_Area(eez_iho.geom)) as area FROM eez_iho GROUP BY iho_sea ORDER BY area DESC |
+ | </file> | ||
+ | |||
+ | Extract latitudes and longitudes of each occurrence for "Delpinus delphis". Note: we have to use a subquery and the ST_Dump function in this case because the whale occurrence data was imported as a MULTIPOINT data and ST_X/ST_Y expects POINT data. | ||
+ | <file postgresql> | ||
+ | SELECT ST_X(geom), ST_Y(geom) FROM (SELECT (ST_Dump(geom)).geom FROM obis_whales WHERE tname='Delphinus delphis') a | ||
</file> | </file> | ||
==== Spatial relationships between layers ==== | ==== Spatial relationships between layers ==== | ||
+ | ST_Contains(geometry A, geometry B): Returns true if and only if no points of B lie in the exterior of A, and at least one point of the interior of B lies in the interior of A. | ||
+ | |||
+ | ST_Crosses(geometry A, geometry B): Returns TRUE if the supplied geometries have some, but not all, interior points in common. | ||
+ | |||
+ | ST_Disjoint(geometry A , geometry B): Returns TRUE if the Geometries do not “spatially intersect” - if they do not share any space together. | ||
+ | |||
+ | ST_Distance(geometry A, geometry B): Returns the 2-dimensional cartesian minimum distance (based on spatial ref) between two geometries in projected units. | ||
+ | |||
+ | ST_DWithin(geometry A, geometry B, radius): Returns true if the geometries are within the specified distance (radius) of one another. | ||
+ | |||
+ | ST_Equals(geometry A, geometry B): Returns true if the given geometries represent the same geometry. Directionality is ignored. | ||
+ | |||
+ | ST_Intersects(geometry A, geometry B): Returns TRUE if the Geometries/Geography “spatially intersect” - (share any portion of space) and FALSE if they don’t (they are Disjoint). | ||
+ | |||
+ | ST_Overlaps(geometry A, geometry B): Returns TRUE if the Geometries share space, are of the same dimension, but are not completely contained by each other. | ||
+ | |||
+ | ST_Touches(geometry A, geometry B): Returns TRUE if the geometries have at least one point in common, but their interiors do not intersect. | ||
+ | |||
+ | ST_Within(geometry A , geometry B): Returns true if the geometry A is completely inside geometry B | ||
+ | |||
+ | Count the occurrences of each species of whales found in Canadian waters. | ||
+ | <file postgresql> | ||
+ | SELECT a.tname, count(*) as num FROM obis_whales a, eez_iho b WHERE ST_Within(a.geom,b.geom) AND b.country='Canada' GROUP BY a.tname ORDER BY num DESC | ||
+ | </file> | ||
+ | |||
+ | |||
+ | <file postgresql> | ||
+ | SELECT a.* FROM obis_whales a, tm_world b WHERE ST_DWithin(a.geom,b.geom,1) AND b.name='Canada | ||
+ | </file> | ||
+ | |||
+ | ++++ Doing it with a distance in meters | | ||
+ | |||
+ | <file postgresql> | ||
+ | ALTER TABLE obis_whales ADD column geog GEOGRAPHY(MULTIPOINT,4326) | ||
+ | </file> | ||
+ | |||
+ | <file postgresql> | ||
+ | UPDATE obis_whales SET geog=geography(geom) | ||
+ | </file> | ||
+ | |||
+ | <file postgresql> | ||
+ | ALTER TABLE tm_world ADD column geog GEOGRAPHY(MULTIPOINT,4326) | ||
+ | </file> | ||
+ | |||
+ | <file postgresql> | ||
+ | UPDATE tm_world SET geog=geography(geom) | ||
+ | </file> | ||
+ | |||
+ | <file postgresql> | ||
+ | SELECT a.* FROM obis_whales a, tm_world b WHERE ST_DWithin(a.geog,b.geog,1) AND b.name='Canada | ||
+ | </file> | ||
+ | |||
+ | ++++ | ||
<file postgresql> | <file postgresql> | ||
CREATE TABLE ce03_gbif_occ AS SELECT a.*, count(b.geom) as num_occ FROM cer03 a LEFT JOIN gbif_mammals b ON (ST_Within(a.geom,b.geom)) GROUP BY a.id | CREATE TABLE ce03_gbif_occ AS SELECT a.*, count(b.geom) as num_occ FROM cer03 a LEFT JOIN gbif_mammals b ON (ST_Within(a.geom,b.geom)) GROUP BY a.id |