This extension contains plugins that add geospatial capabilities to CKAN. The following plugins are currently available:

• Spatial model for CKAN datasets and automatic geo-indexing (spatial_metadata)
• Spatial search integration and API call (spatial_query).
• Map widget integrated on the search form (spatial_query_widget).
• Map widget showing a dataset extent (dataset_extent_map).
• A Web Map Service (WMS) previewer (wms_preview).

Note: All plugins except the WMS previewer require the spatial_metadata plugin.

You will need CKAN installed. The present module should be installed at least with setup.py develop if not installed in the normal way with setup.py install or using pip or easy_install.

The extension uses the GeoAlchemy and Shapely libraries. You can install them via pip install -r pip-requirements.txt from the extension directory.

If you want to use the spatial search API, you will need PostGIS installed and enable the spatial features of your PostgreSQL database. See the "Setting up PostGIS" section for details.

Note that Shapely requires libgeos to be installed. If you installed PostGIS on the same machine you already got it, but if PostGIS is located on another server you will need to install GEOS:

sudo apt-get install libgeos-c1

You will first need to have have PostGIS installed and configured in your database (see the "Setting up PostGIS" section for details)

Once this is done, you need to create the necessary DB tables running the following command (with your python env activated):

paster --plugin=ckanext-spatial spatial initdb [srid] --config=mysite.ini

You can define the SRID of the geometry column. Default is 4326. If you are not familiar with projections, we recommend to use the default value.

Check the Troubleshooting section if you get errors at this stage.

Plugins are configured as follows in the CKAN ini file (Add only the ones you are interested in):

ckan.plugins = spatial_metadata spatial_query spatial_query_widget dataset_extent_map wms_preview

When enabling the spatial metadata, you can define the projection in which extents are stored in the database with the following option. Use the EPSG code as an integer (e.g 4326, 4258, 27700, etc). It defaults to 4326:

ckan.spatial.srid = 4326

If you want to define a default map extent for the different map widgets, (e.g. if you are running a national instace of CKAN) you can do so adding this configuration option:

ckan.spatial.default_map_extent=<minx>,<miny>,<maxx>,<maxy>

Coordinates must be in latitude/longitude, e.g.:

ckan.spatial.default_map_extent=-6.88,49.74,0.50,59.2

The Dataset Extent Map displays only on certain routes. By default it is just the 'Package' controller, 'read' method. To display it on other routes you can specify it in a space separated list like this:

ckan.spatial.dataset_extent_map.routes = package/read ckanext.dgu.controllers.package:PackageController/read

The Dataset Extent Map provides two different map types. It defaults to 'osm' but if you have a license and apikey for 'os' then you can use that map type using this configuration:

ckan.spatial.dataset_extent_map.map_type = os

The Dataset Extent Map will be inserted by default at the end of the dataset page. This can be changed by supplying an alternative element_id to the default:

ckan.spatial.dataset_extent_map.element_id = dataset

If using Spatial Query functionality then there is an additional SOLR/Lucene setting that should be used to set the limit on number of datasets searchable with a spatial value.

The setting is maxBooleanClauses in the solrconfig.xml and the value is the number of datasets spatially searchable. The default is 1024 and this could be increased to say 16384. For a SOLR single core this will probably be at /etc/solr/conf/solrconfig.xml. For a multiple core set-up, there will me several solrconfig.xml files a couple of levels below /etc/solr. For that case, ALL of the cores' solrconfig.xml should have this setting at the new value.

Example:

<maxBooleanClauses>16384</maxBooleanClauses>

This setting is needed because PostGIS spatial query results are fed into SOLR using a Boolean expression, and the parser for that has a limit. So if your spatial area contains more than the limit (of which the default is 1024) then you will get this error:

Dataset search error: ('SOLR returned an error running query...

and in the SOLR logs you see:

too many boolean clauses
...
Caused by: org.apache.lucene.search.BooleanQuery$TooManyClauses:
maxClauseCount is set to 1024

Here are some common problems you may find when installing or using the extension:

• When initializing the spatial tables:

  LINE 1: SELECT AddGeometryColumn('package_extent','the_geom', E'4326...
         ^
  HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
   "SELECT AddGeometryColumn('package_extent','the_geom', %s, 'GEOMETRY', 2)" ('4326',)

  PostGIS was not installed correctly. Please check the "Setting up PostGIS" section. :

  sqlalchemy.exc.ProgrammingError: (ProgrammingError) permission denied for relation spatial_ref_sys

  The user accessing the ckan database needs to be owner (or have permissions) of the geometry_columns and spatial_ref_sys tables.

• When performing a spatial query:

  InvalidRequestError: SQL expression, column, or mapped entity expected - got '<class 'ckanext.spatial.model.PackageExtent'>'

  The spatial model has not been loaded. You probably forgot to add the spatial_metadata plugin to your ini configuration file. :

  InternalError: (InternalError) Operation on two geometries with different SRIDs

  The spatial reference system of the database geometry column and the one used by CKAN differ. Remember, if you are using a different spatial reference system from the default one (WGS 84 lat/lon, EPSG:4326), you must define it in the configuration file as follows:

  ckan.spatial.srid = 4258

Please note that the tests currently only work with Postgres. You must use the test-core.ini located in the extension directory to run them and have the pyenv activated. Most of the time you should run something like:

nosetests --ckan --with-pylons=test-core.ini ckanext/spatial/tests

The following operations can be run from the command line using the paster spatial command:

initdb [srid]
  - Creates the necessary tables. You must have PostGIS installed
  and configured in the database.
  You can privide the SRID of the geometry column. Default is 4326.

extents
   - creates or updates the extent geometry column for datasets with
    an extent defined in the 'spatial' extra.

The commands should be run from the ckanext-spatial directory and expect a development.ini file to be present. Most of the time you will specify the config explicitly though:

paster spatial extents --config=../ckan/development.ini

To enable the spatial query you need to add the spatial_query plugin to your ini file (See Configuration). This plugin requires the spatial_metadata plugin.

The extension adds the following call to the CKAN search API, which returns datasets with an extent that intersects with the bounding box provided:

/api/2/search/dataset/geo?bbox={minx,miny,maxx,maxy}[&crs={srid}]

If the bounding box coordinates are not in the same projection as the one defined in the database, a CRS must be provided, in one of the following forms:

• urn:ogc:def:crs:EPSG::4326
• EPSG:4326
• 4326

As of CKAN 1.6, you can integrate your spatial query in the full CKAN search, via the web interface (see the Spatial Query Widget) or via the action API, e.g.:

POST http://localhost:5000/api/action/package_search
{
    "q": "Pollution",
    "extras": {
        "ext_bbox": "-7.535093,49.208494,3.890688,57.372349"
    }
}

In order to make a dataset queryable by location, an special extra must be defined, with its key named 'spatial'. The value must be a valid GeoJSON geometry, for example:

{"type":"Polygon","coordinates":[[[2.05827, 49.8625],[2.05827, 55.7447], [-6.41736, 55.7447], [-6.41736, 49.8625], [2.05827, 49.8625]]]}

or:

{ "type": "Point", "coordinates": [-3.145,53.078] }

Every time a dataset is created, updated or deleted, the extension will synchronize the information stored in the extra with the geometry table.

Note: this plugin requires CKAN 1.6 or higher.

To enable the search map widget you need to add the spatial_query_widget plugin to your ini file (See Configuration). You also need to load both the spatial_metadata and the spatial_query plugins.

When the plugin is enabled, a map widget will be shown in the dataset search form, where users can refine their searchs drawing an area of interest.

To enable the dataset map you need to add the dataset_map plugin to your ini file (See Configuration). You need to load the spatial_metadata plugin also.

When the plugin is enabled, if datasets contain a 'spatial' extra like the one described in the previous section, a map will be shown on the dataset details page.

To enable the WMS previewer you need to add the wms_preview plugin to your ini file (See Configuration).

Please note that this is an experimental plugin and may be unstable.

When the plugin is enabled, if datasets contain a resource that has 'WMS' format, a 'View available WMS layers' link will be displayed on the dataset details page. It forwards to a simple map viewer that will attempt to load the remote service layers, based on the GetCapabilities response.

• Install PostGIS:

  sudo apt-get install postgresql-8.4-postgis

• Create a new PostgreSQL database:

  sudo -u postgres createdb [database]

  (If you just want to spatially enable an exisiting database, you can ignore this point, but it's a good idea to create a template to make easier to create new databases)

• Many of the PostGIS functions are written in the PL/pgSQL language, so we need to enable it in our database:

  sudo -u postgres createlang plpgsql [database]

• Run the following commands. The first one will create the necessary tables and functions in the database, and the second will populate the spatial reference table:

  sudo -u postgres psql -d [database] -f /usr/share/postgresql/8.4/contrib/postgis-1.5/postgis.sql
  sudo -u postgres psql -d [database] -f /usr/share/postgresql/8.4/contrib/postgis-1.5/spatial_ref_sys.sql

  Note: depending on your distribution and PostGIS version, the scripts may be located on a slightly different location, e.g.:

  /usr/share/postgresql/8.4/contrib/postgis.sql

• Execute the following command to see if PostGIS was properly installed:

  sudo -u postgres psql -d [database] -c "SELECT postgis_full_version()"

  You should get something like:

  postgis_full_version

  ------------------------------------------------------------------------------------------------------POSTGIS="1.5.2" GEOS="3.2.2-CAPI-1.6.2" PROJ="Rel. 4.7.1, 23 September 2009" LIBXML="2.7.7" USE_STATS (1 row)

  Also, if you log into the database, you should see two tables, geometry_columns and spatial_ref_sys (and probably a view called geography_columns).

  Note: This commands will create the two tables owned by the postgres user. You probably should make owner the user that will access the database from ckan:

  ALTER TABLE spatial_ref_sys OWNER TO [your_user];
  ALTER TABLE geometry_columns OWNER TO [your_user];

More information on PostGIS installation can be found here:

http://postgis.refractions.net/docs/ch02.html#PGInstall

If you are loading a database dump to an existing PostGIS database, you may find errors like :

ERROR:  type "spheroid" already exists

This means that the PostGIS functions are installed, but you may need to create the necessary tables anyway. You can force psql to ignore these errors and continue the transaction with the ON_ERROR_ROLLBACK=on:

sudo -u postgres psql -d [database] -f /usr/share/postgresql/8.4/contrib/postgis-1.5/postgis.sql -v ON_ERROR_ROLLBACK=on

You will still need to populate the spatial_ref_sys table and change the tables permissions. Refer to the previous section for details on how to do it.

Note: If you run the initdb command, the table was already created for you. This section just describes what's going on for those who want to know more.

To be able to store geometries and perform spatial operations, PostGIS needs to work with geometry fields. Geometry fields should always be added via the AddGeometryColumn function:

CREATE TABLE package_extent(
    package_id text PRIMARY KEY
);

ALTER TABLE package_extent OWNER TO [your_user];

SELECT AddGeometryColumn('package_extent','the_geom', 4326, 'POLYGON', 2);

This will add a geometry column in the package_extent table called the_geom, with the spatial reference system EPSG:4326. The stored geometries will be polygons, with 2 dimensions (The actual table on CKAN uses the GEOMETRY type to support multiple geometry types).

Have a look a the table definition, and see how PostGIS has created three constraints to ensure that the geometries follow the parameters defined in the geometry column creation:

# \d package_extent

   Table "public.package_extent"
   Column   |   Type   | Modifiers
------------+----------+-----------
 package_id | text     | not null
 the_geom   | geometry |
Indexes:
    "package_extent_pkey" PRIMARY KEY, btree (package_id)
Check constraints:
    "enforce_dims_the_geom" CHECK (st_ndims(the_geom) = 2)
    "enforce_geotype_the_geom" CHECK (geometrytype(the_geom) = 'POLYGON'::text OR the_geom IS NULL)
    "enforce_srid_the_geom" CHECK (st_srid(the_geom) = 4326)