search

cityjson / specs

Specifications for CityJSON, a JSON-based encoding for 3D city models
https://cityjson.org
Creative Commons Zero v1.0 Universal
107 stars 25 forks source link

Normals orientation #157

Closed I-Sokolov closed 1 year ago

I-Sokolov commented 1 year ago

Has cityJSON any agreements and/or requirements for normals orientation and consistency for rings (loops) of surfaces? Can we trust CCW for outer rings and CW for holes? Must surfaces be drawn two- or one-sided? Maybe these things are inherited from cityGML? I'd like to see some hints in the documentaion.

hugoledoux commented 1 year ago

Good point, the specs should mention this indeed.

Basically: it's inherited from CityGML and ISO19107 is used for the primitives.

The relevant rules are explained there: https://val3dity.readthedocs.io/en/latest/definitions/

Can we trust CCW for outer rings and CW for holes?

Yes, if you look at the surface from the outside

Must surfaces be drawn two- or one-sided?

one-sided