About External Data References

Autodesk Civil 3D creates and maintains a point database file that contains all the point information in the project.

COGO points store the point number, name (optional), northing, easting, elevation, and description in each drawing.

You can also reference your own customized databases and use them to do the following:

• Substitute point elevation data when points are accessed through a point group.

• Substitute point raw description data.

To link these custom point databases to Autodesk Civil 3D, create External Data References (XDRefs). An XDRef is a pointer to an entire column of data in a custom Microsoft Access database. All of the database entries must have a point number. Then, when you use an XDRef to get a value for a point, the point number is looked up in the custom database, and the value from the specified column is used instead of the original point value that is stored in the drawing.

XDRefs do not overwrite or alter the points in the drawing. Use the External Data Reference collection on the Settings tree in Toolspace to create and manage XDRefs.

External Data Reference Requirements

The custom databases that you can use for XDRefs must have the following features:

• They must be Microsoft Access database files.

• There must be a Long Integer field index column, which contains the point numbers, in each table in the database that can be used as an XDREF.

• Currently, only Integer, Long Integer, Single, Double, and Text type fields are supported.

• Any number of Tables can be defined in this database, but any that are referenced by XDRefs must have an index column defined.

• Any number of additional Text or Number columns may also be defined in this database table. There are no restrictions on the names and order of the columns after the index column.

• XDRefs are stored on the Settings tab in Toolspace under the Point collection.