plv8_geo

A postgis extension with PLV8 functions for geospatial data

This extension will load a couple of hand-picked javascript geometry-related libraries into your postgres database to use them with plv8. At the moment the following libraries are included (also see the js directory):

• d3: 4.7.4,
• d3-contour: 1.1.0,
• d3-force: 1.0.6,
• d3-geo: 1.6.3,
• d3-hexbin: 0.2.2,
• delaunator: 1.0.2,
• earcut: 2.1.1
• geotiff: 0.4.1,
• topojson: 3.0.0,
• jsts: 1.4.0

Docker support

Run database with everything installed on Docker:

$ docker run -p 5432:5432 geodan/postgis_plv8_geo

login with: postgres/postgres

Command for building image:

$ docker build -t geodan/postgis_plv8_geo .

Manual Installation

Prerequisites

PostgreSQL 9.4 with PL/v8 2.0.3 [https://github.com/plv8/plv8]

note: PLv8 2.0.3 packages not available yet, requires manual build See the instructions over here: https://github.com/plv8/plv8/blob/master/doc/plv8.md#installing-plv8 (make sure to use make static in order to get the latest v8 engine) Older plv8 packages do not support newer ECMAscript version and therefor most libraries do not work (even refuse to install)

Build

On a linux machine (tested on Ubuntu 17.04), clone the git repository and run:

make
sudo make install

Note: the make step is only needed when you want to add libraries yourself. It would be necessary to edit the Makefile in order for these libraries to be loaded.

Test

You can test to see if the library will load and run on your system with:

make installcheck (optional: PGUSER=username PGHOST=myhost etc..)

Create extension

In your sql prompt run CREATE EXTENSION plv8geo This will put all the plv8geo stuff into a new schema called plv8. Functions will be available from this schema.

In order to have the libraries loaded at startup time, add the following to postgresql.conf: plv8.startproc = 'plv8.plv8_startup'

Available functions

plv8.d3_totopojson

Usage:

SELECT plv8.d3_totopojson(<featurecollection>::JSONB)

Returns topology

plv8.d3_simplifytopology

Usage:

SELECT plv8.d3_simplifytopology(<topology>::JSONB,<factor>::numeric)

Returns topology::JSONB

plv8.d3_mergetopology

Usage:

SELECT plv8.mergetopology(<topojson>::JSONB,<propertykey>::TEXT)

Merges the features ins the topology based on a common property. Return set of geojson::JSONB features

plv8.d3_topologytofeatures

Usage:

SELECT plv8.d3_topologytofeatures(<topojson>::JSONB)

Returns set of geojson features

plv8.d3_contour

Usage:

WITH foo AS (
	SELECT ST_SetValue(ST_AddBand(ST_MakeEmptyRaster(3, 3, 0, 0, 1, -1, 0, 0, 0), 1, '8BUI', 1, 0), 1, 2, 5) AS rast
) 
SELECT plv8.d3_contour(array_to_json(ST_DumpValues(rast, 1))) AS values FROM foo;

plv8.d3_hexbin

Usage:

SELECT plv8.d3_hexbin(<array of [x,y]::JSON,<array of keys>::JSON,radius::INTEGER);

returns setof JSONB with {x:centerx, y:centery, data:[{all points in hexagon, with their data}]}

plv8.delaunator

Usage:

SELECT plv8.delaunator(<multipoint>::JSONB)

returns JSONB

plv8.earcut

Usage:

SELECT plv8.earcut(<geometry>::JSONB)

returns JSONB with GeoJSON of multipolygon

plv8.jsts_voronoi

Usage:

SELECT plv8.jsts_voronoi(<multipoint geometry>::JSONB)

returns JSONB with GeoJSON of multipolygon

Examples

Simplify an existing set of geometries topologically

WITH geojson as (
	SELECT json_build_object(
	'type', 'FeatureCollection',
	'features', json_agg(
		json_build_object(
			'type',          'Feature',
			'geometry',  ST_AsGeoJSON(ST_ForceRHR(geom))::json,
			'properties', ('{"ogc_fid":' || ogc_fid || '}')::jsonb
		)
	)
	)::jsonb as geojson 
	FROM france.departement
)
, topojson as (
	SELECT plv8.d3_totopojson(geojson, 1e8) topojson FROM geojson
)
, simplified as (
	SELECT plv8.d3_simplifytopology(topojson, 0.01) simplifiedtopojson FROM topojson
)
, features as (
	SELECT plv8.d3_topologytofeatures(simplifiedtopojson) geojsonfeature FROM simplified
)
SELECT 
	st_setsrid(st_geomFromGeoJson(geojsonfeature->>'geometry'),4326) as geom,
  (geojsonfeature->'properties'->>'ogc_fid')::integer as ogc_fid 
FROM features;

Create contours out of a raster

select plv8.plv8_startup();
do language plv8 'load_module("d3")';
do language plv8 'load_module("d3-contour")';
do language plv8 'load_module("geotiff")';
SET postgis.gdal_enabled_drivers = 'ENABLE_ALL';


WITH foo AS (
	SELECT ST_SetValue(ST_AddBand(ST_MakeEmptyRaster(3, 3, 0, 0, 1, -1, 0, 0, 0), 1, '8BUI', 1, 0), 1, 2, 5) AS rast
) 
,args AS (
	SELECT ROW(1, '-10-300:-10-300', '16BUI', NULL)::reclassarg arg
)
SELECT plv8.d3_contour(
ST_AsTiff(
ST_Reclass(
rast,arg
)
),10) AS values FROM args,foo;

Run delaunator over a set of 10000 points

WITH points AS (
	SELECT ST_GeneratePoints(ST_MakeEnvelope(0,0,100,100),10000) geom
)
SELECT plv8.delaunator(ST_AsGeoJson(geom)::JSONB)
FROM points

Do a hexbin aggregate over a set of 3 points

SELECT plv8.d3_hexbin(('[[1,2],[0.5,0.5],[2,2]]')::json,'["foo","bar","baz"]'::JSON,1);

Run earcut on a polygon

SELECT plv8.earcut(ST_AsGeoJson(ST_MakeEnvelope(0,0,10,10))::JSONB);

Create a voronoi out of 10k points

WITH points as (
	SELECT ST_GeneratePoints(ST_MakeEnvelope(0,0,100,100),10000) geom
)
,jsts AS (
	SELECT ST_GeomFromGeoJson(plv8.jsts_voronoi(ST_AsGeoJson(geom)::jsonb)::text) geom FROM points
),
geos AS ( --added exactly the same function from geos for comparison
	SELECT ST_VoronoiPolygons(geom) geom FROM points
)
SELECT (ST_Dump(geom)).geom FROM jsts