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GeoCouch, a spatial index for CouchDB

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README.md

Welcome to the world of GeoCouch

GeoCouch is a spatial extension for Apache CouchDB and Couchbase.

Prerequisites

A working installation of CouchDB with corresponding source code. GeoCouch works best with Couchbase and the latest stable releases of CouchDB (should be >= 1.1.0).

If you want to use the geometry search, you also need to have GEOS [1] installed on your system.

Understanding the branches:

This repository contains several branches, please make sure you use the correct one:

  • master: works with the CouchDB master branch from Couchbase's repo (https://github.com/couchbase/couchdb)
  • couchdb1.1.x: works with Apache CouchDB 1.1.x
  • couchdb1.2.x: works with Apache CouchDB 1.2.x
  • there is currently no branch for Apache CouchDB 1.3.x

Installation

Get GeoCouch:

git clone https://github.com/couchbase/geocouch.git
cd geocouch

Get dependencies for geometry search

./rebar get-deps

Compilation

Note: Always replace <vanilla-couch> with the path to your CouchDB source and <geocouch> with the location of the GeoCouch source.

Set the COUCH_SRC environment to the directory that contains the CouchDB core source (<vanilla-couch>/src/couchdb/).

export COUCH_SRC=<vanilla-couch>/src/couchdb

Run "make" in your directory

make

Copy the configuration file for GeoCouch from <geocouch>/etc/couchdb/default.d/ to <vanilla-couch>/etc/couchdb/default.d/

cp <geocouch>/etc/couchdb/default.d/geocouch.ini <vanilla-couch>/etc/couchdb/default.d/

Futon tests

To make sure your installation is working also copy the Futon tests over (from <geocouch>/share/www/script/test to <vanilla-couch>/share/www/script/test):

cp <geocouch>/share/www/script/test/* <vanilla-couch>/share/www/script/test/

Add the test to <vanilla-couch>/share/www/script/couch_tests.js

loadTest("spatial.js");
loadTest("list_spatial.js");
loadTest("etags_spatial.js");
loadTest("multiple_spatial_rows.js");
loadTest("spatial_compaction.js");
loadTest("spatial_design_docs.js");
loadTest("spatial_bugfixes.js");
loadTest("spatial_offsets.js");
loadTest("spatial_opensearch.js");

Run CouchDB with GeoCouch

The compiled beam files from GeoCouch need to be in Erlang's path, which can be set with the ERL_FLAGS environment variable. As GeoCouch has additional dependencies (Wkt and Erlgeom) you need to include those in the path as well:

export ERL_FLAGS="-pa <geocouch>/ebin -pa <geocouch>/deps/wkt/ebin -pa <geocouch>/deps/erlgeom/ebin"

If you run a dev instance with CouchDB's ./utils/run you can also define it on startup:

ERL_FLAGS="-pa <geocouch>/ebin -pa <geocouch>/deps/wkt/ebin -pa <geocouch>/deps/erlgeom/ebin" <vanilla-couch>/utils/run

Using GeoCouch

Create a database:

curl -X PUT http://127.0.0.1:5984/places

Add a Design Document with a spatial function:

curl -X PUT -d '{"spatial":{"points":"function(doc) {\n    if (doc.loc) {\n        emit({\n            type: \"Point\",\n            coordinates: [doc.loc[0], doc.loc[1]]\n        }, [doc._id, doc.loc]);\n    }};"}}' http://127.0.0.1:5984/places/_design/main

Put some data into it:

curl -X PUT -d '{"loc": [-122.270833, 37.804444]}' http://127.0.0.1:5984/places/oakland
curl -X PUT -d '{"loc": [10.898333, 48.371667]}' http://127.0.0.1:5984/places/augsburg

Make a bounding box request:

curl -X GET 'http://localhost:5984/places/_design/main/_spatial/points?bbox=0,0,180,90'

It should return:

{"update_seq":3,"rows":[
{"id":"augsburg","bbox":[10.898333,48.371667,10.898333,48.371667],"geometry":{"type":"Point","coordinates":[10.898333,48.371667]},"value":["augsburg",[10.898333,48.371667]]}
]}

The Design Document Function

function(doc) { if (doc.loc) { emit({ type: "Point", coordinates: [doc.loc[0], doc.loc[1]] }, [doc._id, doc.loc]); }};"

It uses the emit() from normal views. The key is a GeoJSON geometry, the value is any arbitrary JSON. All geometry types (even GemetryCollections) are supported.

If the GeoJSON geometry contains a bbox property it will be used instead of calculating it from the geometry (even if it's wrong, i.e. is not the actual bounding box).

Bounding box search and the date line

A common problem when performing bounding box searches is the date line/poles. As the bounding box follows the GeoJSON specification, where the first two numbers are the lower left coordinate, the last two numbers the upper right coordinate, it is easy to map it over the date line/poles. The lower coordinate would have a higher value than the upper one. Such a bounding box has a seems invalid at first glance, but isn't. For example a bounding box like 110,-60,-30,15 would include Australia and South America, but not Africa.

GeoCouch operates on a plane and doesn't perform spherical calculations. Therefore the bounds of the plane needs to be set explicitly with the plane_bounds parameter. If bounding boxes are flipped, a search across those bounds will be performed automatically. Give it a try (with the same Design Document as above). Insert some Documents:

curl -X PUT -d '{"loc": [17.15, -22.566667]}' http://127.0.0.1:5984/places/namibia
curl -X PUT -d '{"loc": [135, -25]}' http://127.0.0.1:5984/places/australia
curl -X PUT -d '{"loc": [-52.95, -10.65]}' http://127.0.0.1:5984/places/brasilia

And request only Australia and Brasilia:

curl -X GET 'http://localhost:5984/places/_design/main/_spatial/points?bbox=110,-60,-30,15&plane_bounds=-180,-90,180,90'

The result is as expected:

{"update_seq":6,"rows":[
{"id":"australia","bbox":[135,-25,135,-25],"geometry":{"type":"Point","coordinates":[135,-25]},"value":["australia",[135,-25]]},
{"id":"brasilia","bbox":[-52.95,-10.65,-52.95,-10.65],"geometry":{"type":"Point","coordinates":[-52.95,-10.65]},"value":["brasilia",[-52.95,-10.65]]}
]}

The bounding with the same numbers, but different order (-30,-60,110,15) would only return Namibia:

curl -X GET 'http://localhost:5984/places/_design/main/_spatial/points?bbox=-30,-60,110,15&plane_bounds=-180,-90,180,90'

{"update_seq":6,"rows":[
{"id":"namibia","bbox":[17.15,-22.566667,17.15,-22.566667],"geometry":{"type":"Point","coordinates":[17.15,-22.566667]},"value":["namibia",[17.15,-22.566667]]}
]}

List function support

GeoCouch supports List functions just as CouchDB does for Views. This way you can output any arbitrary format, e.g. GeoRSS.

As an example we output the points as WKT. Add a new Design Document with an additional List function (the rest is the same as above). Make sure you use the right _rev:

curl -X PUT -d '{"_rev": "1-121efc747b00743b8c7621ffccf1ac40", "lists": {"wkt": "function(head, req) {\n    var row;\n    while (row = getRow()) {\n        send(\"POINT(\" + row.geometry.coordinates.join(\" \") + \")\\n\");\n    }\n};"}, "spatial":{"points":"function(doc) {\n    if (doc.loc) {\n        emit({\n            type: \"Point\",\n            coordinates: [doc.loc[0], doc.loc[1]]\n        }, [doc._id, doc.loc]);\n    }};"}}' http://127.0.0.1:5984/places/_design/main

Now you can request this List function as you would do for CouchDB, though with a different Design handler (_spatial/_list instead of _list ):

curl -X GET 'http://localhost:5984/places/_design/main/_spatial/_list/wkt/points?bbox=-180,-90,180,90'

The result is:

POINT(10.898333 48.371667)
POINT(-122.270833 37.804444)
POINT(17.15 -22.566667)
POINT(135 -25)
POINT(-52.95 -10.65)

Using List functions from Design Documents other than the one containing the Spatial functions is supported as well. This time we add the Document ID in parenthesis:

curl -X PUT -d '{"lists": {"wkt": "function(head, req) {\n    var row;\n    while (row = getRow()) {\n        send(\"POINT(\" + row.geometry.coordinates.join(\" \") + \") (\" + row.id + \")\\n\");\n    }\n};"}}' http://127.0.0.1:5984/places/_design/listfunonly

curl -X GET 'http://localhost:5984/places/_design/listfunonly/_spatial/_list/wkt/main/points?bbox=-180,-90,180,90'

Geometry search

The most common geometry search is probably polygon search, though all geometries as specified in the OpenSearch Geo (Draft 2) Specification 2 are supported.

Here's an example request with a polygon, spaces are encoded as "+".

curl -X GET 'http://localhost:5984/places/_design/main/_spatial/points?geometry=POLYGON((-21.0+58.9,+21.0+-61.1,+113.9+-54.3,+150.4+72.289067198883,+-21.0+58.9))'

{"update_seq":8,"rows":[
{"id":"augsburg","bbox":[10.898333,48.371667,10.898333,48.371667],"geometry":{"type":"Point","coordinates":[10.898333,48.371667]},"value":["augsburg",[10.898333,48.371667]]},
{"id":"namibia","bbox":[17.15,-22.566667,17.15,-22.566667],"geometry":{"type":"Point","coordinates":[17.15,-22.566667]},"value":["namibia",[17.15,-22.566667]]}
]}

If you want to make a polygon request over the date line or poles, split it and make it a MultiPolygon.

Other supported query arguments

stale

stale=ok is supported. The spatial index won't be rebuilt even if new Documents were added. It works for normal spatial queries as well as for the spatial List functions.

count

count is a boolean. count=true will only return the number of geometries the query will return, not the geometry themselves.

curl -X GET 'http://localhost:5984/places/_design/main/_spatial/points?bbox=0,0,180,90&count=true'

{"count":1}

limit

With limit you can limit the number of rows that should be returned.

curl -X GET 'http://localhost:5984/places/_design/main/_spatial/points?bbox=-180,-90,180,90&limit=2'

{"update_seq":8,"rows":[
{"id":"augsburg","bbox":[10.898333,48.371667,10.898333,48.371667],"geometry":{"type":"Point","coordinates":[10.898333,48.371667]},"value":["augsburg",[10.898333,48.371667]]},
{"id":"oakland","bbox":[-122.270833,37.804444,-122.270833,37.804444],"geometry":{"type":"Point","coordinates":[-122.270833,37.804444]},"value":["oakland",[-122.270833,37.804444]]}
]}

skip

With skip you start to return the results at a certain offset.

curl -X GET 'http://localhost:5984/places/_design/main/_spatial/points?bbox=-180,-90,180,90&skip=3'

{"update_seq":8,"rows":[
{"id":"australia","bbox":[135,-25,135,-25],"geometry":{"type":"Point","coordinates":[135,-25]},"value":["australia",[135,-25]]},
{"id":"brasilia","bbox":[-52.95,-10.65,-52.95,-10.65],"geometry":{"type":"Point","coordinates":[-52.95,-10.65]},"value":["brasilia",[-52.95,-10.65]]}
]}

Compaction, cleanup and info

The API of GeoCouch's spatial indexes is similar to the one for the Views. Compaction of spatial indexes is per Design Document, thus:

curl -X POST 'http://localhost:5984/places/_design/main/_spatial/_compact' -H 'Content-Type: application/json'

To cleanup spatial indexes that are no longer in use (this is per database):

curl -X POST 'http://localhost:5984/places/_spatial_cleanup' -H 'Content-Type: application/json'

To get information about the spatial indexes of a certain Design Document use the the _info handler:

curl -X GET 'http://localhost:5984/places/_design/main/_spatial/_info'

References

[1] http://trac.osgeo.org/geos [2] http://www.opensearch.org/Specifications/OpenSearch/Extensions/Geo/1.0/Draft_2

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