22 Using GeoJSON Geographic Data

Example 22-1 A Table With GeoJSON Data

This example creates table j_geo, which has a column, geo_doc of GeoJSON documents.

Only one such document is inserted here. It contains a GeoJSON object of type FeatureCollection, and a features array of objects of type Feature. Those objects have geometry, respectively, of type Point, LineString, and Polygon.

CREATE TABLE j_geo
  (id      VARCHAR2 (32) NOT NULL,
   geo_doc VARCHAR2 (4000) CHECK (geo_doc IS JSON));

INSERT INTO j_geo
  VALUES (1,
          '{"type"     : "FeatureCollection",
            "features" : [{"type"       : "Feature",
                           "geometry"   : {"type" : "Point",
                                           "coordinates" : [-122.236111, 37.482778]},
                           "properties" : {"Name" : Redwood City"}},
                          {"type" : "Feature",
                           "geometry" : {"type" : "LineString",
                                         "coordinates" : [[102.0, 0.0],
                                                          [103.0, 1.0],
                                                          [104.0, 0.0],
                                                          [105.0, 1.0]]},
                           "properties" : {"prop0" : "value0",
                                           "prop1" : 0.0}},
                          {"type"        : "Feature",
                            "geometry"   : {"type" : "Polygon",
                                            "coordinates" : [[[100.0, 0.0],
                                                              [101.0, 0.0],
                                                              [101.0, 1.0],
                                                              [100.0, 1.0],
                                                              [100.0, 0.0]]]},
                            "properties" : {"prop0" : "value0",
                                            "prop1" : {"this" : "that"}}}]}');

Example 22-2 Selecting a geometry Object From a GeoJSON Feature As an SDO_GEOMETRY Instance

This example uses SQL/JSON function json_value to select the value of field geometry from the first element of array features. The value is returned as Oracle Spatial and Graph data, not as JSON data, that is, as an instance of PL/SQL object type SDO_GEOMETRY, not as a SQL string or LOB instance.

SELECT json_value(geo_doc, '$.features[0].geometry'
                  RETURNING SDO_GEOMETRY 
                  ERROR ON ERROR)
  FROM j_geo;

The value returned is this, which represents a point with longitude and latitude (coordinates) -122.236111 and 37.482778, respectively.

SDO_GEOMETRY(2001, 4326, SDO_POINT_TYPE(-122.236111, 37.482778, NULL), NULL, NULL)

Example 22-3 Retrieving Multiple geometry Objects From a GeoJSON Feature As SDO_GEOMETRY

This example uses SQL/JSON function json_table to project the value of field geometry from each element of array features, as column sdo_val of a virtual table. The retrieved data is returned as SDO_GEOMETRY.

SELECT jt.*
  FROM j_geo,
       json_table(geo_doc, '$.features[*]'
         COLUMNS ("sdo_val" SDO_GEOMETRY PATH '$.geometry')) jt;

The following three rows are returned for the query. The first represents the same Point as in Example 22-2. The second represents the LineString array. The third represents the Polygon.

SDO_GEOMETRY(2001, 4326, SDO_POINT_TYPE(-122.236111, 37.482778, NULL), NULL, NULL)

SDO_GEOMETRY(2002, 4326, NULL, SDO_ELEM_INFO_ARRAY(1, 2, 1), SDO_ORDINATE_ARRAY(102, 0, 103, 1, 104, 0, 105, 1))

SDO_GEOMETRY(2003, 4326, NULL, SDO_ELEM_INFO_ARRAY(1, 1003, 1), SDO_ORDINATE_ARRAY(100, 0, 101, 0, 101, 1, 100, 1, 100, 0))

The second and third elements of attribute SDO_ELEM_INFO_ARRAY specify how to interpret the coordinates provided by attribute SDO_ORDINATE_ARRAY. They show that the first row returned represents a line string (2) with straight segments (1), and the second row represents a polygon (2003) of straight segments (1).

Example 22-4 Creating a Spatial Index For GeoJSON Data

This example creates a json_value function-based index of type MDSYS.SPATIAL_INDEX on field geometry of the first element of array features. This can improve the performance of queries that use json_value to retrieve that value.

CREATE INDEX json_geo_index
  ON j_geo (json_value(geo_doc, '$.features[0].geometry'
                       RETURNING SDO_GEOMETRY))
  INDEXTYPE IS MDSYS.SPATIAL_INDEX;

Example 22-5 Using GeoJSON Geometry With Spatial Operators

This example selects the documents (there is only one in this table) for which the geometry field of the first features element is within 100 kilometers of a given point. The point is provided literally here (its coordinates are the longitude and latitude of San Francisco, California). The distance is computed from this point to each geometry object.

The query orders the selected documents by the calculated distance. The tolerance in meters for the distance calculation is provided in this query as the literal argument 100.

SELECT id,
       json_value(geo_doc, '$features[0].properties.Name') "Name",
       SDO_GEOM.sdo_distance(
         json_value(geo_doc, '$features[0].geometry') RETURNING SDO_GEOMETRY,
         SDO_GEOMETRY(2001,
                      4326,
                      SDO_POINT_TYPE(-122.416667, 37.783333, NULL),
                      NULL,
                      NULL),
         100, -- Tolerance in meters
         'unit=KM') "Distance in kilometers"
  FROM  j_geo
  WHERE sdo_within_distance(
          json_value(geo_doc, '$.features[0].geometry' RETURNING SDO_GEOMETRY),
          SDO_GEOMETRY(2001,
                       4326,
                       SDO_POINT_TYPE(-122.416667, 37.783333, NULL),
                       NULL,
                       NULL),
          'distance=100 unit=KM')
        = 'TRUE';

The query returns a single row:

ID    Name           Distance in kilometers
-------------------------------------------
1     Redwood City   26.9443035