The Extract command is used to subdivide and extract curves from database shell entities to make them easier to use. Many shell entities only contain shape information. They do not have any internal topology to attach grid to specific locations. Using Extract, you can create curves at natural breaks in the geometry and subdivide shells into small pieces along these feature lines.

Extract Panel
Use the Extract command to subdivide and extract curves from database shell entities.

Select shell(s) to be extracted, then Edit, Extract. Specify the Split Angle, if different than the default 45.0 degrees. Specify whether curves and/or shells are extracted in the Extract frame. If necessary, modify the shell selection in the Selection frame. Click Extract to perform a feature extraction.

Extract Boundary
Use the Extract command to subdivide one selected shell and extract curves.

As seen in the figure above, the thick yellow lines shown in the Display window indicate the boundaries of the candidate shells resulting from the extract operation. The object counts of Selected Shells, Extracted Shells, and Extracted Curves will be updated accordingly in the table at the top of the panel.

If the extraction is not satisfactory, change the extraction settings, then click Extract again. Click OK to save the new shells and/or curves, or click Apply to save your changes and continue extracting curves and/or shells. Otherwise, click Cancel to exit the Extract panel without saving any changes.

Extract Shells
New shells (colored differently) are created resulting from the Extract operation.

The Split Angle command controls the extraction process. Database shell entities are composed of triangular facets. If the bend angle between two adjacent triangle facets is greater than the entered Split Angle, the edge they share is considered a candidate feature for curve/surface extraction.

To change the Split Angle, type in a new value (0-180) in the Split Angle text field. Selecting Extract again will redo the extraction with the new Split Angle.


The Extract frame is used to specify whether a candidate feature will be extracted as a curve, shell, or both.

  • Shells subdivides a shell using closed boundaries or a loop that closes with the boundary of the shell.
  • Curves assembles features into database curves (polylines). Contiguous features are joined into a single curve for easier reference during grid construction and other database operations.


The controls in the Selection frame let you choose precisely which shell entities to extract.

  • Begin allows you to start the shell entity selection process within the Display window or List panel. The text on this button changes to End and the button remains depressed until clicked to end selection.
  • Cancel allows you to end the shell selection process without changing the target status.
Extract Selection
Use Selection to specify a subset of Extract target shell entities.