2010-05-03
10:29
An idea has become reality. Exactly two years after the
blog post with the initial vision,
a new version of GeoCouch is finished. It's a huge step forward. The first time
the dependencies were narrowed down to CouchDB
itself. No Python,
no SpatiaLite any longer, it's pure
Erlang. GeoCouch is tightly integrated with
CouchDB, so you'll get all the nice features you love about CouchDB.
Current implementation
Thanks to the feedback after the FOSS4G 2009 and
"GeoCouch: The future" blog entry"
it was clear that people prefer a simple, yet powerful and tightly integrated
approach, rather than having to many external dependencies (which was a
showstopper for quite a few people).
I implemented an R-tree (I call it vtree as the implementation is
subject to change a lot) from scratch. The reason why I haven't used
the already existing R-Tree implementation available at
Github is that I needed
something to learn Erlang, it doesn't contain test or examples and
that it is always a good idea to implement a data structure yourself
to understand the details/problems. My implementation is far from
being perfect but works good enough for now. The vtree is implemented
as an append-only data structure just as CouchDB's B-trees
are. Currently it doesn't support bulk insertion.
If you want to know details on how to create your own indexer, have a look at
my Indexer tutorial.
Feature set
Following the "Release early, release often" philosophy currently only points
can be inserted, the only supported query is a bounding box search. Though
other geometries should follow soon.
Using GeoCouch
GeoCouch is now hosted
at Github. Giving GeoCouch a go is easy:
git clone http://github.com/vmx/couchdb.git
cd couchdb
./bootstrap
./configure
make dev
./utils/run
To try the spatial features when it's up and running is easy as well. Just add
a spatial property and a named function to your Design Document as you
would to for
show or list functions:
function(doc) {
if (doc.loc) {
emit(doc._id, {
type: "Point",
coordinates: [doc.loc[0], doc.loc[1]]
});
}
};
All you need to do is emitting GeoJSON as the value
(Remember that point is the only supported geometry at the moment), the
key is currently ignored.
curl -X PUT http://127.0.0.1:5984/places
curl -X PUT -d '{"spatial":{"points":"function(doc) {\n if (doc.loc) {\n emit(doc._id, {\n type: \"Point\",\n coordinates: [doc.loc[0], doc.loc[1]]\n });\n }};"}}' http://127.0.0.1:5984/places/_design/main
Before a bounding box query can return anything, you need to insert Documents
that contain a location.
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
And finally you can make a bounding box request:
curl -X GET 'http://localhost:5984/places/_design/main/_spatial/points/%5B0,0,180,90%5D'
This one should return only augsburg:
{"query1":[{"id":"augsburg","loc":[10.898333,48.371667]}]}
Next steps
The development of GeoCouch was quite slow in the past, but it gets up
to speed as my diploma thesis (comparable to a master's thesis) will be
about GeoCouch. Additionally Couchio kindly
supports the development.
The next steps are (in no particular order):
- Better R-tree (better splitting algorithm, bulk operations)
- Supporting more geometries
- Polygon search
- Improving CouchDB's plugin capabilities
Thanks
I'd like to thank all the people that kept me motivated over the past two
years with their tremendous feedback. Special thanks go to
Jan Lehnardt for getting me onto the Couch,
Cameron Shorter for introducing me
into the geospatial open source business and all people from
Couchio for the
great two weeks in Oakland.
Categories:
en,
CouchDB,
Python,
Erlang,
geo
