This is an important agreement as SIG 3D memebers defined the first version of CityGML (which I have posted about in the past), essentially an open data model framework/encoding standard for 3D virtual cities. This agreement moves closer to something that many researchers (but also developers) have been debating for for years, i.e. a more accepted/official/standardized format in this field. This will be boosted by the Open Geospatial Consortium's authority and credentials as it consists of currently over 410 government agencies, research institutions, industry partners and Universities.
More information about CityGML and the Open Geospatial Consortium can be found here and here.