Placement and Dimensions
A PlacementSpecification is used to define the Placement of OccurrenceOrUsages in a topology as physical elements that build this topology and to define Dimensions between these elements. Each PlacementSpecification is a container for various Placements and Dimensions.
Each OccurrenceOrUsage that is placeable in the topology defines a PlaceableElementRole. A PlaceableElementRole can define various PlacementPointReferences and MeasurementPointReferences, which are instances of the corresponding elements PlacementPoint and MeasurementPoint defined in the part master data of the component. The position in the topology of a PlaceableElementRole is defined with a Placement. The multiplicity of this association is caused by the support of variance in the VEC. For a concrete configuration, there should be only one Placement for one PlaceableElementRole.
The VEC specifies two individual types of Placements: OnPointPlacements and OnWayPlacements.
Each OnPointPlacement defines one or more Locations in order to determine the positioning of the placedElement. More than one Location is necessary to specify the exact Placement of placedElements with more than one PlacementPointReferences, e.g. the different entries in case of a cable duct. Each Location can therefore reference a PlacementPointReference.
An OnWayPlacement references one Location as startLocation and another Location as endLocation in order to determine the positioning of placedElements like tapes that cover a way in the topology. The positioning can be described even more precise by using the OnWayPlacement with a Path through the topology.
Both OnPointPlacements and OnWayPlacements reference one or more PlaceableElementRoles as placedElements. The possibility to reference more than just one PlaceableElementRole permits to express that configuration dependant the one or other PlaceableElementRole is placed. Finally, both OnPointPlacements and OnWayPlacements can reference other Placements on which they are placed on top of in order to determine the arrangement of layering (e.g. a tape around a tube).
Note: When using the isOnTopOf-relationship all other underlying Placements shall be referenced on which the referencing Placement is on top of and not only the direct neighbour. The reason for this is that Placements are ConfigurableElements and so are potentially not present in all configurations.
Since the VEC can be used to exchange a product definition, it must be possible to define Dimensions with tolerances between the elements in addition to its exact positions in the topology.
Each Dimension references two DimensionAnchor, one as referenceAnchor and one as dimensionAnchor and defines the distance in between as dimensionValue, optionally together with a tolerance (included in the definition of NumericalValue). In case of ambiguity regarding the path between the two Locations, the Dimension shall specify the relevant Path.
A DimensionAnchor can be either a MeasurementPointReference or a Location. A MeasurementPointReference is used when the Dimension should reference an element on the component which is outside of the topology (e.g. a certain edge or a bolt). If a Location is referenced it can be either a Location defined by a Placement (if the dimension should reference the position of a component) or a Location defined by the Dimension itself if an element of the topology with no component on it must be referenced (e.g. a TopologyNode).