MSSQL

Author:Tamas Szekeres
Contact:szekerest at gmail.com
Author:Jeff McKenna
Contact:jmckenna at gatewaygeomatics.com
Last Updated:2012-09-26

Introduction

Microsoft SQL Server 2008+ supports storing spatial data by using the built-in geometry/geography data types. MapServer can connect to MSSQL through either: 1) an OGR connectiontype, or 2) a driver that accesses 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. You can easily upload existing data to an MSSQL table by using the ogr2ogr commandline tool and the OGR’s MSSQL Spatial driver Here is an example that uploads a shapefile (province.shp) into an MSSQL 2008 instance:

ogr2ogr -f MSSQLSpatial -a_srs EPSG:4326 "MSSQL:server=.\SQLEXPRESS;database=geo;trusted_connection=yes" province.shp

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

OPTION 1: Connect Through OGR

GDAL/OGR (and therefore MapServer) can read spatial tables in MSSQL 2008 through the MSSQLSpatial driver.

Verify Local Support for MSSQLSpatial

Use the command “ogrinfo –formats” to verify that your local GDAL is built with support for MSSQL; the response should contain “MSSQLSpatial” such as:

Supported Formats:
  -> "OCI" (read/write)
  -> "ESRI Shapefile" (read/write)
  -> "MapInfo File" (read/write)
  ...
  -> "MSSQLSpatial" (read/write)
  ...

Test OGR Connection Parameters

Use the ogrinfo commandline utility to test your connection through the MSSQLSpatial driver, such as:

ogrinfo "MSSQL:server=.\SQLEXPRESS;database=geo;trusted_connection=yes" province -summary

Create MapServer Layer using CONNECTIONTYPE OGR

Your layer should contain a CONNECTIONTYPE OGR statement, as well as a CONNECTION. The connection should also contact a “tables=” parameter, and also the name of the geometry column in brackets. You do not need to specify the DATA parameter unless you define an sql select statement starting with the ‘WHERE’ keyword. For example:

LAYER
  NAME "provinces"
  TYPE POLYGON
  STATUS ON
  ####
  CONNECTIONTYPE OGR
  CONNECTION "MSSQL:server=.\SQLEXPRESS;uid=xx;pwd=xxx;database=geo;trusted_connection=yes;tables=province(ogr_geometry)"
  ####
  PROJECTION
    "init=epsg:4326"
  END
  CLASS
    NAME "Land"
    STYLE
      COLOR 240 240 240
      OUTLINECOLOR 199 199 199
    END
  END
  PROCESSING 'CLOSE_CONNECTION=DEFER'
END # layer

Note

The usual CONNECTIONTYPE terms ‘using unique’ and ‘using srid’ are not meaningful for the OGR driver in this case, as these parameters are automatically retrieved from the ‘geometry_columns’ metadata table.

OPTION 2: Connect Through MapServer Plugin

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"

Expected Location of the MSSQL Plugin

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.

Binaries Containing the MSSQL Plugin

Currently the following binary distributions contain msplugin_mssql2008.dll:

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.
  • MSSQL_READ_WKB=TRUE - Uses WKB (Well Known Binary) format instead of native format when fetching geometries.

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