A DGN file is composed of models. When you draw or place elements with Promis.e tools, the elements are added to the active model. A model can be either 2D or 3D, and is stored as a discrete object within the DGN file. There are three types of models: design, drawing, and sheet.
Design models, which are similar to DWG models (model space), consist of design geometry and can be either 2D or 3D. A design model can also be used as a reference or placed as a cell. You can create an unlimited number of design models in a DGN file. In contrast, the DWG file format allows only one model per file.
Drawing models, which are also similar to DWG models (model space), are a subset of a 2D or 3D design model, used to apply annotations, dimensions, callouts, and other embellishments to a design. You can create an unlimited number of drawing models in a DGN file. In contrast, the DWG file format allows only one model per file.
Sheet models, which are similar to DWG drawing layouts (paper space), are most commonly used composing finished and annotated drawings. You can create an unlimited number of sheet models per DGN file. The DWG file format also allows unlimited drawing layouts.
Working with Models That Will Be Saved to DWG Files
The DWG file format allows one model and unlimited drawing layouts. When you are working with models in a DGN file that you plan to save to a DWG file, the easiest way to ensure compatibility is to use only one design or drawing model with unlimited sheet models.
When you save a DGN model to a DWG file, the default design model is saved to model space in the DWG file, and the sheet models are saved to drawing layouts. The Save As DWG/DXF Options dialog provides several options for saving non-default design and drawing models:
- The Create Separate Files option saves each non-default design or drawing model to a separate DWG file. Reference attachments to non-default models are saved to XREF inserts pointing to the new separate model DWG files.
- The Create Paper Space option saves each non-default design or drawing model to a drawing layout (paper space) in the DWG model that contains the default design model. Reference attachments are merged according to the Non-Default Models Attachments setting on the Save As DWG/DXF Options dialog.
- The Ignore option does not save the non-default models to the DWG file. Reference attachments are merged according to the Non-Default Models Attachments setting on the Save As DWG/DXF Options dialog.