# Topological Information

Once the geometry set has been defined, it serves as the base of all other investigations carried out. The topology engine of the VDA Checker creates adjacency information on demand. Knowledge about one or several connected regions is the result of this computation. Adjacency is computed prior to executing the check routines which rely on this information. Once computed, it will be retained as long as the selected geometry set is not modified or deleted.

To give the user an impression of the topological situation before starting an analysis run, for each connected region the outer boundary may be displayed.

NOTE: For solid bodies ( i.e. the geometry set contains complete ones ) there is no outer boundary under normal circumstances. In case boundaries are displayed this may result from gaps exceeding the Topological Tolerances | Distance or from tiny faces near modelling tolerance.

The user can force the creation or renewal of topological information ( Create/Renew Topology ). For Number of Edge Curve Points the topology engine evaluates the distance between two common edge curve candidates and checks this distance against Topological Tolerances | Distance . A Topological Tolerance defines an upper threshold value beyond which a continuity check criterion violation is neither considered a violation nor logged in the Results Log File. A topological tolerance is defined for distance, angle and curvature ( for GC0, GC1 and GC2 continuity across surface or segment boundaries respectively ).

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