# Reference Geometry

Reference geometry should be represented as flat node based (/XREF) or element based (/EREF) geometry.

In /EREF, the reference geometry parts of the airbag can be separate parts that are not connected.

In some cases, /XREF can also be used to with reference geometry that is not connected. In this case, each part referenced in the card should not connect to itself in the actual airbag model.

- the geometrical center of non-folded airbag should be at point X=0, Y=0, or Z=0
- normal directions of components in reference geometry should be the same as in folded airbag model
- intersections are not allowed in unfolded airbag reference geometry

- each component should be in the Z=0 plane
- the components normal direction in the reference geometry should be the same as in folded airbag model