PostgreSQL/PostGIS


 

PostgreSQL/PostGIS supports spatial extensions to enable the generation, storage, and analysis of geographic features. Additional information is available at http://postgis.net/

 

AspMap supports the Geometry and Geography data types. The PostgreSqlLayer class can be used to access and edit such spatial data. A sample table in a PostgreSQL database may look as the following:

NAME            TYPE
--------------------------------------
ID              serial
CITY_NAME       character varying(40)
STATE_NAME      character varying(25)
POPULATION      integer
GEOM              geometry

CREATE INDEX cities_geom ON cities USING gist (GEOM)

 

The GEOM field stores shapes in the Geometry data format. The GEOM field has a spatial index (USING gist GEOM) which is required to speed up spatial queries (for fast map rendering).

 

The ADO.NET framework does not have a built-in provider for PostgreSQL. The Npgsql provider (or any other PostgreSQL provider) is required. The Npgsql provider can be downloaded at http://npgsql.projects.pgfoundry.org/

 

Create a PostgreSqlLayer object and pass the connection string, table name and GEOM field to its constructor. It is also necessary to specify the FieldList property if you need attribute data for labeling or editing. Depending on the spatial data type, the DataType property should be specified.

 

Add the PostgreSqlLayer to the Map control using the AddLayer method:

Imports Npgsql
Imports AspMap
Imports AspMap.Data

Dim connectionString As String = "Server=localhost;Database=DB;User ID=username;Password=password;"
Dim tableName As String = "cities"
Dim providerName As String = "Npgsql"

Dim postgreLayer As PostgreSqlLayer 

postgreLayer = New PostgreSqlLayer (providerName, connectionString, tableName, "GEOM")
postgreLayer.FieldList = "ID, CITY_NAME, POPULATION"
postgreLayer.DataType = PostgreSqlDataType.Geometry

Dim layer As Layer = map.AddLayer(postgreLayer)

 

The PostgreSqlLayer class supports editing of data as described in the Editing Spatial and Attribute Data topic.

 

Note: If you use only database layers in your application, it must be necessary to specify the extent of each database layer. By default, the extent is set to (-180,90,180,-90) where the units are decimal degrees. The extent of a database layer can be set via the Extent property. If an incorrect extent is set, the database layer will not be visible.

 

 

 

 


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