Taimoor Zaeem
055921eaf5
For better visibility. Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>
138 lines
3.7 KiB
ReStructuredText
138 lines
3.7 KiB
ReStructuredText
.. _ww_postgis:
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PostGIS
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=======
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You can use the string representation for `PostGIS <https://postgis.net/>`_ data types such as ``geometry`` or ``geography`` (you need to `install PostGIS <https://postgis.net/documentation/getting_started/>`_ first).
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.. code-block:: postgres
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-- Activate the postgis module in the current database
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create extension if not exists postgis;
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create table coverage (
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id int primary key,
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name text unique,
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area geometry
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);
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To add areas in polygon format, you can use string representation:
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.. code-block:: bash
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curl "http://localhost:3000/coverage" \
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-X POST -H "Content-Type: application/json" \
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-d @- << EOF
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[
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{ "id": 1, "name": "small", "area": "SRID=4326;POLYGON((0 0, 1 0, 1 1, 0 1, 0 0))" },
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{ "id": 2, "name": "big", "area": "SRID=4326;POLYGON((0 0, 10 0, 10 10, 0 10, 0 0))" }
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]
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EOF
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Now, when you request the information, PostgREST will automatically cast the ``area`` column into a ``Polygon`` geometry type. Although this is useful, you may need the whole output to be in `GeoJSON <https://geojson.org/>`_ format out of the box, which can be done by including the ``Accept: application/geo+json`` in the request. This will work for PostGIS versions 3.0.0 and up and will return the output as a `FeatureCollection Object <https://www.rfc-editor.org/rfc/rfc7946#section-3.3>`_:
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.. code-block:: bash
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curl "http://localhost:3000/coverage" \
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-H "Accept: application/geo+json"
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.. code-block:: json
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{
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"type": "FeatureCollection",
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"features": [
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{
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"type": "Feature",
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"geometry": {
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"type": "Polygon",
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"coordinates": [
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[[0,0],[1,0],[1,1],[0,1],[0,0]]
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]
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},
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"properties": {
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"id": 1,
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"name": "small"
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}
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},
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{
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"type": "Feature",
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"geometry": {
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"type": "Polygon",
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"coordinates": [
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[[0,0],[10,0],[10,10],[0,10],[0,0]]
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]
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},
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"properties": {
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"id": 2,
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"name": "big"
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}
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}
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]
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}
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If you need to add an extra property, like the area in square units by using ``st_area(area)``, you could add a generated column to the table and it will appear in the ``properties`` key of each ``Feature``.
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.. code-block:: postgres
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alter table coverage
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add square_units double precision generated always as ( st_area(area) ) stored;
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In the case that you are using older PostGIS versions, then creating a function is your best option:
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.. code-block:: postgres
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create or replace function coverage_geo_collection() returns json as $$
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select
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json_build_object(
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'type', 'FeatureCollection',
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'features', json_agg(
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json_build_object(
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'type', 'Feature',
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'geometry', st_AsGeoJSON(c.area)::json,
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'properties', json_build_object('id', c.id, 'name', c.name)
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)
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)
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)
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from coverage c;
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$$ language sql;
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Now this query will return the same results:
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.. code-block:: bash
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curl "http://localhost:3000/rpc/coverage_geo_collection"
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.. code-block:: json
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{
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"type": "FeatureCollection",
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"features": [
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{
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"type": "Feature",
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"geometry": {
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"type": "Polygon",
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"coordinates": [
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[[0,0],[1,0],[1,1],[0,1],[0,0]]
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]
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},
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"properties": {
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"id": 1,
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"name": "small"
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}
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},
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{
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"type": "Feature",
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"geometry": {
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"type": "Polygon",
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"coordinates": [
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[[0,0],[10,0],[10,10],[0,10],[0,0]]
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]
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},
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"properties": {
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"id": 2,
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"name": "big"
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}
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}
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]
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}
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