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Geospatial Index and Query

Use Aerospike geospatial storage, indexing, and query to enable fast queries on points within a region, on a region containing points, and points within a radius.

Underlying technologies​

The Aerospike geospatial feature relies on these technologies:

info

The S2 Geometry Library is a spherical geometry library, very useful for manipulating regions on a sphere (commonly on Earth) and indexing geographic data. Also, review the S2 blog for details on S2, Hilbert Curve, and Geospatial mapping.

Use Cases​

  • Vehicle tracking systems that require high throughput updates of vehicle location and frequently query vehicles within a region.
  • Retail locations to find specific amenities within 500m of a shopper.
  • Location-targetted bidding transactions to discover persons or devices within the location with an active ad campaign.

See these Aerospike examples.

Geospatial Data​

Aerospike supports the GeoJSON geospatial data type. All geospatial functionality (indexing and querying) only execute on GeoJSON data types.

GeoJSON data incurs this additional processing on data reads:

  • GeoJSON text is parsed for validity and support (see GeoJSON Parsing).
  • GeoJSON text is converted into S2 CellID coverings.
  • Aerospike saves both the covering CellIDs and the original GeoJSON in the database.
  • Only GeoJSON data is accessible to the application through the client APIs and the UDF subsystem.

Geospatial Index​

In addition to integers and strings, Aerospike supports Geo2DSphere data types for indexes.

This example aql script creates a Geo2DSphere data type index:

aql> CREATE INDEX my_geo_index ON test.demoset (geobin) GEO2DSPHERE

Geo2DSphere indexes behave as other index types to:

  • Scan existing records to inspect the indexed bin (geobin in the example above) to build an in-memory geospatial index.
  • Create an independent index for data on each node.
  • Update the index on all subsequent data inserts and updates.
  • Rebuild the index when a node restarts.

Geospatial Query​

Aerospike supports two Geospatial queries:

  • Points within a region (including circle)
  • Region contains point

Points-within-Region—Circle Query​

This example to Python script is a points-within-a-region query.

def query_pwr(args,client):

    """Construct a GeoJSON region."""
    region = aerospike.GeoJSON({
        'type': 'Polygon',
        'coordinates': [[[-122.500000,37.000000],
                         [-121.000000, 37.000000],
                         [-121.000000, 38.080000],
                         [-122.500000, 38.080000],
                         [-122.500000, 37.000000]]]})

    """Construct the query predicate."""
    query = client.query(args.nspace, args.set)
    predicate = aerospike.predicates.geo_within_geojson_region(LOCBIN, region.dumps())
    query.where(predicate)

    """Define callback to process query result."""
    def callback((key, metadata, record)):
        records.append(record)

    """Make the actual query!"""

    query.foreach(callback)

Example for points-within-a-region query using AQL.

  • Insert a point data into aerospike.
aql> INSERT INTO test.testset (PK, geo_query_bin) VALUES (2, GEOJSON('{"type": "Point", "coordinates": [1,1]}'))
  • Querying a region to see if it contains that point.
aql> SELECT * FROM test.testset WHERE geo_query_bin CONTAINS GeoJSON('{"type":"Polygon", "coordinates": [[[0,0], [0, 10], [10, 10], [10, 0], [0,0]]]}'))
+----------------------------------------------------+
| geo_query_bin                                      |
+----------------------------------------------------+
| GeoJSON('{"type": "Point", "coordinates": [1,1]}') |
+----------------------------------------------------+
1 row in set (0.004 secs)

Region-Contains-Points Query​

This example C++ script is a region-contains-points query.

// Callback function to process each record response
bool
query_cb(const as_val * valp, void * udata)
{
    if (!valp)
        return true;    // query complete

    char const * valstr = NULL;

    as_record * recp = as_record_fromval(valp);
    if (!recp)
        fatal("query callback returned non-as_record object");
    valstr = as_record_get_str(recp, g_valbin);

    __sync_fetch_and_add(&g_numrecs, 1);

    cout << valstr << endl;

    return true;
}

// Main query function
void
query_prcp(aerospike * asp, double lat, double lng)
{
    char point[1024];

    // Construct a GeoJSON point.
    snprintf(point, sizeof(point),
             "{ \"type\": \"Point\", \"coordinates\": [%0.8f, %0.8f] }",
             lng, lat);

    // Construct the query object.
    as_query query;
    as_query_init(&query, g_namespace.c_str(), g_set.c_str());

    as_query_where_inita(&query, 1);
    as_query_where(&query, g_rgnbin, as_geo_contains(point));

    // Make the actual query.
    as_error err;
    if (aerospike_query_foreach(asp, &err, NULL,
                                &query, query_cb, NULL) != AEROSPIKE_OK)
        throwstream(runtime_error,
                    "aerospike_query_foreach() returned "
                    << err.code << '-' << err.message);

    as_query_destroy(&query);
}

Example for region-contains-points query using AQL.

  • Insert a region data into aerospike.
aql> INSERT INTO test.testset (PK, geo_query_bin) VALUES (1, GEOJSON('{"type": "Polygon", "coordinates": [[[0,0], [0, 10], [10, 10], [10, 0], [0,0]]]}'))
  • Query a point in that region.
AQL> SELECT * FROM test.testset WHERE geo_query_bin CONTAINS GeoJSON('{"type":"Point", "coordinates": [1, 1]}')
+---------------------------------------------------------------------------------------------+
| geo_query_bin                                                                               |
+---------------------------------------------------------------------------------------------+
| GeoJSON('{"type": "Polygon", "coordinates": [[[0,0], [0, 10], [10, 10], [10, 0], [0,0]]]}') |
+---------------------------------------------------------------------------------------------+
1 row in set (0.017 secs)

Query Filters​

To extend the capabilities of both queries, use UDFs to filter the result set.

This example Python script demonstrates using a filter UDF.

def query_circle(args, client):
    """Query for records inside a circle."""
    query = client.query(args.nspace, args.set)
    predicate = aerospike.predicates.geo_within_radius(LOCBIN,
                                                       args.longitude,
                                                       args.latitude,
                                                       args.radius)
    query.where(predicate)

    # Search with UDF amenity filter
    query.apply('filter_by_amenity', 'apply_filter', [args.amenity,])
    query.foreach(print_value)

Where the apply_filter Lua function is the following:

local function select_value(rec)
  return rec.val
end

function apply_filter(stream, amen)
  local function match_amenity(rec)
    return rec.map.amenity and rec.map.amenity == amen
  end
  return stream : filter(match_amenity) : map(select_value)
end

Index on list/map​

It is also possible to index and query on list/map elements with GeoJSON data type -

# create a secondary index for numeric values of test.demo records whose 'points' bin is a list of GeoJSON points
client.index_list_create('test', 'demo', 'points', aerospike.INDEX_GEO2DSPHERE, 'demo_point_nidx')

predicate = aerospike.predicates.geo_within_radius('points',
                                                    args.longitude,
                                                    args.latitude,
                                                    args.radius,
                                                    aerospike.INDEX_GEO2DSPHERE)

query = client.query('test', 'demo')
query.where(predicate);

The above will create an index on geoJSON list elements, and construct the query predicate using the index.

Aerospike GeoJSON Extension​

Use the Aerospike AeroCircle geometry object to store circles along with regular polygons.

This example script specifies a circle with a radius of 300 meters at longitude/latitude -122.250629, 37.871022.

{"type": "AeroCircle", "coordinates": [[-122.250629, 37.871022], 300]}

GeoJSON Parsing​

On data insert/update, Aerospike only recognizes Point, Polygon, MultiPolygon, and AeroCircle GeoJSON geometry objects, which are indexable objects. Unsupported GeoJson objects return an AS_PROTO_RESULT_FAIL_GEO_INVALID_GEOJSON error (for example, LineString or MultiLineString fail on insert). Holes can be Polygon objects, per the GeoJSON Format Specification.

note

Polygon loop definitions must wind counter-clockwise.

Aerospike supports the Feature operator, which allows groups of geometry objects and user-specified properties; however, Feature Collection is not supported.

Invalid GeoJSON objects are caught on insert/update. For example, an object defined as point instead of Point fails.

Per the GeoJSON IETF recommendation, the Coordinate System is WGS84. Explicit specification of CRS is ignored.

Create a Geospatial Application​

To develop a geospatial application:

  1. Install and configure the Aerospike server.
  2. Create a Geo2DSphere index on a namespace-set-bin combination.
  3. Construct and insert GeoJSON Point data.
  4. Construct a Points-within-Region predicate (where clause), make a query request, and process the records returned.
  5. (alternate) Construct and insert GeoJSON Polygon/MultiPolygon data.
  6. (alternate) Construct a Region-contains-Point predicate, make a query request, and process the records returned.

Known Limitations​

  • Using UDFs to insert/update of GeoJSON data types is not supported.
  • Duplicate records can be returned.
  • For namespaces with data-in-memory true, GeoJSON particles allocate up to 2KB more than the reported particle size, which can lead to high memory consumption in some cases. This problem has been corrected in Aerospike Server versions 4.9.0+, 4.8.0.8, 4.7.0.12, 4.6.0.14, 4.5.3.16, 4.5.2.16, 4.5.1.21, 4.5.0.24.
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