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MSSQL

Author:Tamas Szekeres
Contact:szekerest at gmail.com
Last Updated:2010-10-01

Introduction

Microsoft SQL Server 2008+ supports storing spatial data by using the built in geometry/geography data types. MapServer supports a driver to access these tables containing spatial columns, which is compiled as a plugin (msplugin_mssql2008.dll).

Creating spatial data tables in MSSQL 2008

There are several ways to create spatial data tables in MSSQL 2008. Having an existing data you can easily upload that to an MSSQL table by using the ogr2ogr commandline tool and the OGR’s MSSQL Spatial driver

Connecting to Spatial Data in MSSQL 2008

In order to connect to the MSSQL 2008 spatial database you should set up a valid connection string to the database like the following examples:

Server=.\MSSQLSERVER2008;Database=Maps;Integrated Security=true
Server=55.55.55.55,1433;uid=a_user;pwd=a_password;database=a_database;Integrated Security=True
Server=55.55.55.55\SQLEXPRESS,1433;uid=a_user;pwd=a_password;database=a_database;Integrated Security=True

Create MapServer Layer

Once the connection can be established to the server the layer can be configured to access MSSQL2008 as follows:

LAYER
  NAME "rivers_mssql_spatial"
  TYPE POLYGON
  STATUS DEFAULT
  CONNECTIONTYPE PLUGIN
  PLUGIN "msplugin_mssql2008.dll"
  CONNECTION "Server=.\MSSQLSERVER2008;Database=Maps;Integrated Security=true"
  DATA "ogr_geometry from rivers USING UNIQUE ogr_fid USING SRID=4326"
  ...
END

The DATA parameter is used to perform the SQL select statement to access your table in MSSQL. The geometry column is required in the select statement; in the above example the ogr_geometry column is the geometry column in the rivers table. The table should also have an unique column (ogr_fid) which is provided for random access to the features in the feature query operations.

The DATA section should also contain the spatial reference id (SRID) of the features in the data table The SRID is used when specifying the search shapes during the intersect operations which should match with the SRID of the features otherwise no features are returned in a particular query. if you omit specifying the SRID value in the DATA section the diver will use SRID=0 when defining the search shapes.

Selecting the type of the geometry column

For the geometry columns MSSQL supports 2 data types: “geometry” and “geography”. By default the driver considers the type of the geometry column is “geometry”. In case if the type of the geometry column is “geography” we must specify the data type in the DATA section explicitly, like:

DATA "ogr_geometry(geography) from rivers USING UNIQUE ogr_fid USING SRID=4326"

The expected location on the plugin dll

On Windows platforms the DLLs needed by the program are searched for in the following order:

  1. The directory from which the application loaded.
  2. The current directory.
  3. The system directory. Use the GetSystemDirectory function to get the path of this directory.
  4. The 16-bit system directory.
  5. The Windows directory. Use the GetWindowsDirectory function to get the path of this directory.
  6. The directories that are listed in the PATH environment variable.

Using spatial indexes

In order to speed up the access to the features a spatial index should be created to the geometry column which could easily be done with the OGR MSSQL Spatial driver like:

ogrinfo -sql "create spatial index on rivers" "MSSQL:server=.\MSSQLSERVER2008;database=Maps;Integrated Security=true"

In general we can safely rely on the query optimizer to select the most appropriate index in the sql query operations. In some cases - however - we should force the optimizer to use the spatial index by specifying the index hint in the DATA section like:

DATA "ogr_geometry from rivers using index ogr_geometry_sidx USING UNIQUE ogr_fid USING SRID=4326"

Layer Processing Options

We can control the behaviour of the MSSQL driver by using the following PROCESSING options:

  • CLOSE_CONNECTION=DEFER - This is where you can enable connection pooling for certain layer types. Connection pooling will allow MapServer to share the handle to an open database or layer connection throughout a single map draw process.

Obtaining binaries containing the MSSQL plugin dll

Currently the following binary distributions contain msplugin_mssql2008.dll

More Information