Used to	Select in the Class Definitions Tools
Define a new class.	Define Class tool
Delete the selected class.	Delete Class tool
Reclassify user defined parts of the point cloud according to defined criteria.	Edit Classification tool
Import classes from another DGN file.	Import Point Cloud Data tool

Any point cloud stored in a POD format can have up to 256 classes to structure the point cloud data. In a POD file those classes are only defined by an identifier between 0 and 255. In order to manipulate those classes in a meaningful way, Bentley Descartes defines those classes with a name and a color. This way point cloud classes can be manipulated and understood by different tools. Class definition in a DGN acts as a dictionary defining how to interpret and display the classes. The Class Definitions tab is used to create new classes, delete existing and import classes from other DGN files.

Class definitions are part of the DGN file and not the point cloud. It is possible to attach a point cloud which has points in classes not explicitly defined in the current DGN file. If that is the case then those classes will be shown as Undefined Classes. The Undefined Classes entry cannot be deleted.

Portions of the point cloud are assigned to different classes using the classification tool. In the point cloud file, only an identifier is associated with the point. So it is possible for two DGN files with the same point cloud attached to show two different class names.