The ModelBuilder3d contains a code example, but this is outdated, since the class is now a singleton.
Fixed in commit 75b44575d51f9f8179ca6f143a823e84ccafcc54 in the cdk-1.2.x branch.
Fixed in commit 75b44575d51f9f8179ca6f143a823e84ccafcc54 in the cdk-1.2.x branch.