> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ntop.com/llms.txt
> Use this file to discover all available pages before exploring further.

# How do I use geometric constraints?

## Question:

How do I use geometric constraints?

## Answer:

A **Planar Symmetry Constraint** can be added to the constraints list to ensure symmetry in the resulting TopOpt part. It is recommended to use a symmetrical FE Mesh that matches the planar symmetry of the TopOpt constraint, using the Mirror FE Mesh block. Although the design space and TopOpt result will be symmetric when this constraint is used, the boundary conditions do not have to be symmetrical.

The **Passive Regions Constraint** specifies a volume in which the topology will not be modified by the TopOpt process. The elements within a passive region will still be considered in the calculations throughout the TopOpt, but TopOpt density will remain 1 there.

The **Extrusion Constraint** will produce a TopOpt part that has a consistent profile along the direction of a specified curve.

![The Extrusion Constraint will produce a TopOpt part that has a consistent profile along the direction of a specified curve.](https://files.learn.ntop.com/help-articles/optimization/360070752793.png)

The **Overhang Angle Constraint** is explained [here](https://support.ntopology.com/hc/en-us/articles/360060738793-How-to-use-the-overhang-constraint-in-Topology-Optimization).

## Keywords:

*mesh list topopt design fe topology symmetry multiple optimization response planar constraint passive objectives structural compliance region overhang extrustion*