Table of Contents for

Web Mapping Illustrated

Types of databases

The VirtualSpatialData OGR extension has been tested with the following databases and should, in theory, support all ODBC data sources.

Types of flat files

Comma, tab, or custom delimited text/flat files work with VirtualSpatialData.

Create the data source name (DSN)

Specific notes about creating a DSN on Windows and Linux can be found by searching the MapServer reference documents site at http://mapserver.gis.umn.edu/doc.

On some Windows systems you must create a SYSTEM DSN.

Test your connection

Test your connection with ogrinfo. The syntax for this command is:

    > ogrinfo ODBC:user/pass@DSN table

ogrinfo examples

Here’s an example that accesses a comma-separated text file through ODBC; it’s a flat text file coal_dep.txt containing lat/long points:

    unknown,na,id,id2,mark,coalkey,coalkey2,long,lat
    0.000,0.000,1,1,7,87,87,76.90238,51.07161
    0.000,0.000,2,2,7,110,110,78.53851,50.69403
    0.000,0.000,3,3,3,112,112,83.22586,71.24420
    0.000,0.000,4,4,6,114,114,80.79896,73.41175

If the DSN name is Data_txt, the ogrinfo command to see a list of applicable files in the directory is:

    > ogrinfo ODBC:jeff/test@Data_txt
    INFO: Open of `ODBC:jeff/test@Data_txt'
    using driver `ODBC' successful.
    1: coal_dep.csv
    2: coal_dep.txt
    3: coal_dep_nf.txt
    4: coal_dep_trim.txt
    5: Copy of coal_dep.txt
    6: deposit.csv
    7: maruia.asc
    8: oahuGISbathy.csv
    9: oahuGISbathy.txt
    10: on_pts.txt
    11: on_pts_utm.txt
    12: test.txt
    13: utm_test.txt

The username and password may be optional, so the following may also be valid:

    > ogrinfo ODBC:@Data_txt

Therefore, the command to see more information about one of the specific layers is:

                  > ogrinfo ODBC:@Data_txt coal_dep.txt
    INFO: Open of 'ODBC:@Data_txt'
    using driver 'ODBC' successful.
     
    Layer name: coal_dep.txt
    Geometry: Unknown (any)
    Feature Count: 266
    Layer SRS WKT:
    (unknown)
    UNKNOWN: String (255.0)
    NA: String (255.0)
    ID: String (255.0)
    ID2: String (255.0)
    MARK: String (255.0)
    COALKEY: String (255.0)
    COALKEY2: String (255.0)
    LONG: String (255.0)
    LAT: String (255.0)
    OGRFeature(coal_dep.txt):0
      UNKNOWN (String) = 0.000
      ....

Here’s an example that creates a virtual data file with an ovf extension:

    <OGRVRTDataSource>
        <OGRVRTLayer name="mylayer">
            <SrcDataSource>ODBC:user/pass@DSN</SrcDataSource>
        <SrcLayer>tablename</SrcLayer>
       <GeometryType>wkbPoint</GeometryType>
            <LayerSRS>WGS84</LayerSRS>
       <GeometryField encoding="PointFromColumns" x="x" y="y"/>
        </OGRVRTLayer>
    </OGRVRTDataSource>

More information on ovf files can be found at http://www.remotesensing.org/gdal/ogr/drv_vrt.html.

Here’s an example ovf file for coal_dep.txt:

    <OGRVRTDataSource>
      <OGRVRTLayer  name="coal">
         <SrcDataSource>ODBC:Data_txt</SrcDataSource>
         <SrcLayer>coal_dep.txt</SrcLayer>
         <GeometryField encoding="PointFromColumns" x="Long" y="Lat"/>
         <GeometryType>wkbPoint</GeometryType>
      </OGRVRTLayer>
    </OGRVRTDataSource>

Map file example

Using an ovf file, your layer may look like:

       LAYER
        CONNECTION "coal.ovf"
        CONNECTIONTYPE OGR
        DATA "coal-test"
          METADATA
            "wms_srs"   "4326"
            "wms_title"   "coal-test"
          END
        NAME "coal-test"
        SIZEUNITS PIXELS
        STATUS ON
        TOLERANCE 0
        TOLERANCEUNITS PIXELS
        TYPE POINT
        UNITS METERS
        CLASS
          STYLE
              COLOR 255 0 0
            MAXSIZE 100
            MINSIZE 1
            SIZE 6
            SYMBOL "star"
          END
        END
      END

You may also specify the ovf contents inline this way:

      LAYER
        CONNECTION "<OGRVRTDataSource>
    <OGRVRTLayer  name='coal-test'>
    <SrcDataSource>ODBC:@Data_txt</SrcDataSource>
    <SrcLayer>coal_dep.txt</SrcLayer>
    <GeometryField encoding='PointFromColumns' x='Long' y='Lat'/>
    <GeometryType>wkbPoint</GeometryType>
    </OGRVRTLayer>
    </OGRVRTDataSource>"
        CONNECTIONTYPE OGR
        DATA "coal-test"
          METADATA
            "wms_srs"   "4326"
            "wms_title"   "coal-test"
          END
        NAME "coal-test"
        SIZEUNITS PIXELS
        STATUS ON
        TOLERANCE 0
        TOLERANCEUNITS PIXELS
        TYPE POINT
        UNITS METERS
        CLASS
          STYLE
              COLOR 255 0 0
            MAXSIZE 100
            MINSIZE 1
            SIZE 6
            SYMBOL "star"
          END
        END
      END