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Spatial Data Types

Backendless database supports the following spatial data types:

  • POINT - represents a single point/location in coordinate space. For the points representing locations on a map, the coordinates are longitude and latitude.
  • LINESTRING - represents a geometry consisting of a collection of points with linear interpolation between them. For example, a linestring can represent a delivery route.
  • POLYGON - a closed geometrical shape consisting of a single exterior boundary and zero or more interior boundaries, also referred to as holes.

Additionally, Backendless supports a "parent" data type called GEOMETRY. This is the base type which can accommodate any of the data types listed above.

database-geo-types.zoom50

Spatial data in Backendless can be represented either in the WKT (Well-Known Text) or the GeoJSON formats. Backendless console supports both of these formats for entering new data or updating existing spatial values. Additionally, Backendless SDKs provide built-in classes which make it easier to work with the spatial data for all database operations, including creating, retrieving, updating and deleting spatial data.

POINT

The POINT type is used to represent a single point identified by two coordinates in a coordinates space. The coordinates are named X and Y, however, Backendless also handles these coordinates as longitude (X) and latitude (Y) to represent locations on a map. The WKT representation of this type is:

POINT (longitude latitude)

or

POINT (x y)

for example, the POINT below points to Dallas, TX

POINT (-96.7553535 32.8656106)

The GeoJSON format for the POINT values is:

{  
  "type": "Point",  
  "coordinates": [  
    longitude or X,  
    latitude or Y  
  ]  
}

A POINT value stored in the database is represented by the Point class in the client application. The class provides access to the point coordinates (x and y) which can also represent longitude and latitude in cases when the point identifies a location on a map. The class has the constructor and methods listed below. Notice that all set methods return the current Point object, which allows for convenient "chaining" for property assignments: pointInstance.setX( value ).setY( value ):

// creates a new instance of Point
Point()

// creates a Point object from a WKT definition
static Point fromWKT<Point>( String wktPoint )

// creates a Point object from a GeoJSON definition
static Point fromGeoJSON<Point>( String geoJSON )

// the X coordinate of the point (same as longitude)
double x

// the Y coordinate of the point (same as latitude)
double y

// retrieves the longitude coordinate of the point (same as x)
double get longitude

// retrieves the latitude coordinate of the point (same as y)
double get latitude


// sets the longitude coordinate of the point (same as x)
set longitude(double longitude)


// sets the latitude ccordinatte of the point (same as y)
set latitude(double latitude)

// converts this Point object into its WKT representation
String asWKT()

// converts this Point object into its GeoJSON representation
String asGeoJSON()

// checks this Point object with another object for equality
bool operator ==(other)

// calculates a hash code of this Point object based on the coordinate values and the SRS code.
int get hashCode()

Consider the following example. The objects shown below contain a geometry column/property called location. The type of the column is POINT:

person-table-location.zoom80

The following code retrieves the first object from the table. Notice how the geometry property is accessed. Backendless automatically converts POINT data type to an instance of the Point class:

Backendless.data.withClass<Person>().findFirst().then((person) {
 var location = person.location;
 var locationLatitude = location.latitude;
 var locationLongitude = location.longitude;
});

LINESTRING

The LINESTRING type is used to represent geometries composed of multiple POINT values with linear interpolation between each two consecutive points. The WKT representation of this type is:

LINESTRING (lon1 lat1, lon2 lat2, lon3 lat3, lon4 lat4)

or

LINESTRING (x1 y1, x2 y2, x3 y3, x4 y4)

for example, the LINESTRING below identifies the main stops of the historic Route 66:

LINESTRING (-87.52683788 41.85716752, -90.13875858 38.68967135, -95.93953983 36.2131248, -97.49959842 35.53656483, -101.8282117 35.26791494, -105.87118045 35.72083154, -106.61825076 35.14794417, -111.63900272 35.20182535, -118.24178592 34.07195769)

The GeoJSON format for the LINESTRING values is:

{  
  "type": "LineString",  
  "coordinates": [  
    [  
      lon1 or x1,  
      lat1 or y1  
    ],  
    [  
      lon2 or x2,  
      lat2 or x2  
    ],  
    [  
      lon3 or x3,  
      lat3 or y3  
    ],  
    [  
      lon4 or x4,  
      lat4 or y4  
    ]  
  ]  
}

Database values of this type are represented by the LineString class in the client application. The class provides access to the Point objects making up the linestring. The class has the constructors and methods as listed below. Notice that all set method return the current LineString object, which allows for convenient "chaining": lineStringInstance.setPoints( value ).asWKT():

// creates a new instance of LineString
LineString(List<Point> points)

// creates a LineString object from a WKT definition
static LineString fromWKT<LineString>( String wktLineString )

// creates a LineString object from a GeoJSON definition
static LineString fromGeoJSON<LineString>( String geoJSON )

// a collection of Point objects making up this LineString
List<Point> points

// converts this LineString object into its WKT representation
String asWKT()

// converts this LineString object into its GeoJSON representation
String asGeoJSON()

// checks this LineString object with another object for equality
bool operator ==(other)

// calculates a hash code of this LineString object based on the coordinates of all Points and the SRS code.
int get hashCode()

Consider the following example. The Travel table has an object identifying a travel route. The route column is of the LINESTRING type, its value is visualized in the map in the screenshot below:

linestring-example.zoom85

The following code retrieves the Travel object from the table, gets its route property (which is a LineString) and accesses the points making up the linestring:

var dataQuery = DataQueryBuilder();
dataQuery.whereClause = "name = 'Route 66'";
Backendless.data.of("Travel").find(dataQuery).then((response) {
 var travelRoute = response[0];
 var routeName = travelRoute["name"];
 var routeDefinition = travelRoute["route"];
 var points = routeDefinition.points;
});

POLYGON

Value of the POLYGON type is a figure that is described by a number of LINESTRING values connected to form a single continuous exterior boundary. Additionally, a Polygon may  contain zero or more interior boundaries, where each interior boundary defines a hole in the Polygon. The WKT representation of this type is:

POLYGON ((lon1 lat1, lon2 lat2, lon3 lat3),  
         (hole-lon1 hole-lat1, hole-lon2 hole-lat2, hole-lon3 hole-lat3),  
         (...),(...))

or

POLYGON ((x1 y1, x2 y2, x3 y3),  
         (hole-x1 hole-y1, hole-x2 hole-y2, hole-x3 hole-y3),  
         (...),(...))

where the first group of coordinates defines the exterior boundary and all subsequent groups defines the holes. The first group is mandatory.

for example, the POLYGON below identifies the outline of The Pentagon - the US Department of Defense headquarters. It also includes a hole - which is the inner plaza.

POLYGON ((-77.05781934 38.87248788,   
          -77.05474017 38.87287211,   
          -77.0533025 38.8706001,   
          -77.05556629 38.86883758,   
          -77.05848453 38.87002374,   
          -77.05781934 38.87248788),   
         (-77.05669282 38.87156906,   
          -77.05551265 38.87170271,   
          -77.05494402 38.8708507,   
          -77.05577014 38.87030775,   
          -77.05688594 38.87074211,   
          -77.05669282 38.87156906))

The GeoJSON format for the POLYGON values is:

{  
  "type": "Polygon",  
  "coordinates": [  
    [  
      [  
        lon1,  
        lat1  
      ],  
      [  
        lon2,  
        lat2  
      ],  
      [  
        lon3,  
        lat3  
      ]  
    ],  
    [  
      [  
        hole-lon1,  
        hole-lat1  
      ],  
      [  
        hole-lon2,  
        hole-lat2  
      ],  
      [  
        hole-lon3,  
        hole-lat3  
      ]  
    ]  
  ]  
}

Database values of this type are represented by the Polygon class in the client application. The class provides access to the LineString objects making up the polygon. The class has the constructors and methods as listed below. Notice that all set method return the current Polygon object, which allows for convenient "chaining" for property assignments: polygonInstance.setBoundary( value ).asWKT():

// creates a new instance of Polygon with the external boundary and (optionally) the holes

Polygon({LineString boundary, List<LineString> holes, SpatialReferenceSystem srs})

// creates a Polygon object from a WKT definition
static Polygon fromWKT<Polygon>( String wktPolygon )

// creates a Polygon object from a GeoJSON definition
static Polygon fromGeoJSON<Polygon>( String geoJSON )

// LineString which defines the external boundary of the polygon
LineString boundary

// a collection of LineString objects each identifying a hole
List<LineString> holes

// converts this Polygon object into its WKT representation
String asWKT()

// converts this Polygon object into its GeoJSON representation
String asGeoJSON()

// checks this Polygon object with another object for equality
bool operator ==(other)

// calculates a hash code of this Polygon object based on the coordinates of the boundary, holes and the SRS code.
int get hashCode()

Consider the following example. The Building table has an object identifying a shape of a building. The shape column is of the POLYGOON type, its value is visualized in the map in the screenshot below:

pentagon-example.zoom80

The following code retrieves the Building object from the table, gets its shape property (which is a Polygon) and accesses its external boundary and the hole.

var dataQuery = DataQueryBuilder();
dataQuery.whereClause = "name = 'Pentagon'";
Backendless.data.of("Building").find(dataQuery).then((response) {
 var building = response[0];
 var buildingName = building["name"];
 var buildingShape = building["shape"];
 var externalBoundary = buildingShape.boundary;
 var holes = buildingShape.holes;
});