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.
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 Backendless.Data.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 )
:
/**
* @public
* @class Backendless.Data.Point
*/
class Point {
// creates a new instance of Point
constructor();
//creates a Point object from a WKT definition
static fromWKT(wellKnownText: string): Backendless.Data.Point;
// creates a Point object from a GeoJSON definition
static fromGeoJSON(geoJSON: string): Backendless.Data.Point;
// retrieves the X coordinate of the point (same as longitude)
public getX(): Number;
// retrieves the Y coordinate of the point (same as latitude)
public getY(): Number;
// retrieves the longitude coordinate of the point (same as x)
public getLongitude(): Number;
// retrieves the latitude coordinate of the point (same as y)
public getLatitude(): Number;
// sets the x coordinate of the point (same as longitude)
public setX(x: Number): Backendless.Data.Point;
// sets the y coordinate of the point (same as latitude)
public setY(y: Number): Backendless.Data.Point;
// sets the longitude coordinate of the point (same as x)
public setLongitude(x: Number): Backendless.Data.Point;
// sets the latitude coordinate of the point (same as y)
public setLatitude(y: Number): Backendless.Data.Point;
// converts this Point object into its WKT representation
public asWKT(): string;
// converts this Point object into its GeoJSON representation
public asGeoJSON(): string;
// checks this Point object with another object for equality
public equals(o: Object): boolean;
}
Consider the following example. The objects shown below contain a geometry column/property called location
. The type of the column is POINT
:
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.mapTableToClass('Person', Person)
Backendless.Data.of(Person).findFirst()
.then(person => {
const location = person.getLocation()
const locationLatitude = location.getLatitude()
const locationLongitude = location.getLongitude()
})
.catch(error => {
})
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 Backendless.Data.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()
:
/**
* @public
* @class Backendless.Data.LineString
*/
class LineString {
constructor(points: Point[]);
// creates a LineString object from a WKT definition
static fromWKT(wellKnownText: string): Backendless.Data.LineString;
// creates a LineString object from a GeoJSON definition
static fromGeoJSON(geoJSON: string): Backendless.Data.LineString;
// returns a collection of Point objects making up this LineString
public getPoints(): Backendless.Data.Point[];
// sets a collection of Point objects to define the LineString
public setPoints(points: Point[]): Backendless.Data.LineString;
// converts this LineString object into its WKT representation
public asWKT(): string;
// converts this LineString object into its GeoJSON representation
public asGeoJSON(): string;
}
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:
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:
const dataQuery = Backendless.DataQueryBuilder.create()
dataQuery.setWhereClause('name = \'Route 66\'')
Backendless.Data.of('Travel').find(dataQuery)
.then(response => {
const travelRoute = response[0]
const routeName = travelRoute.name
const routeDefinition = travelRoute.route
const points = routeDefinition.getPoints()
})
.catch(error => {
})
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 Backendless.Data.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()
:
/**
* @public
* @class Backendless.Data.Polygon
*/
class Polygon {
constructor(boundary: Backendless.Data.LineString | Backendless.Data.Point[], holes?: Backendless.Data.LineString[]);
// creates a Polygon object from a WKT definition
static fromWKT(wellKnownText: string): Backendless.Data.Polygon;
// creates a Polygon object from a GeoJSON definition
static fromGeoJSON(geoJSON: string): Backendless.Data.Polygon;
// returns a LineString which defines the external boundary of the polygon
public getBoundary(): Backendless.Data.LineString;
public setBoundary(boundary: Backendless.Data.LineString | Point[]): Backendless.Data.Polygon;
// returns a collection of LineString objects each identifying a hole
public getHoles(): Backendless.Data.LineString[];
public setHoles(holes: Backendless.Data.LineString[]): Backendless.Data.Polygon;
// converts this Polygon object into its WKT representation
public asWKT(): string;
// converts this Polygon object into its GeoJSON representation
public asGeoJSON(): string;
}
Consider the following example. The Building
table has an object identifying a shape of a building. The shape
column is of the POLYGON
type, its value is visualized in the map in the screenshot below:
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.
const dataQuery = Backendless.DataQueryBuilder.create()
dataQuery.setWhereClause('name = \'Pentagon\'')
Backendless.Data.of('Building').find(dataQuery)
.then(response => {
const building = response[0]
const buildingName = building.name
const buildingShape = building.shape
const externalBoundary = buildingShape.getBoundary()
const holes = buildingShape.getHoles()
})
.catch(error => {
})