4.5.9.4. CityObjectGroup

When exporting city object groups, also group members are written to the target dataset (cf. Section 4.5.7). Group members are always exported by reference. For CityGML, this means that the grp:member property of a CityObjectGroup does not contain the member inline but uses an xlink:href reference to point to the member. In CityJSON, the "members" property of a CityObjectGroup is per definition just an array of the identifiers of the group members. In both cases, the group members themselves are therefore exported as separate top-level features in the same dataset.

Fig. 4.43 Export preferences – CityObjectGroup.

By default, group members are only exported if they satisfy the export filter settings. This behavior can be changed using this preference dialog. When checking the option Export all group members as references only, then a reference is created for each group member of a CityObjectGroup defined in the database, no matter whether this group member is also exported or skipped due to filter settings. Thus, the consistency of the references is not checked, and some references might not be resolvable in the final dataset. The benefit of skipping this check is that the overall performance of the export is increased.