Involved in the biosynthesis of the labdane-type bicyclic diterpene labda-8(17),12(E),14-triene. Catalyzes the conversion of geranylgeranyl diphosphate (GGDP) into (+)-copalyl diphosphate. (2E,6E,10E)-geranylgeranyl diphosphate = (+)-copalyl diphosphate The Asp-Xaa-Asp-Asp-Thr-Ala (DXDDTA) and Gln-Xaa-Xaa-Asp-Gly-Ser-Trp (QXXDGSW) motifs are expected to bind to Mg(2+). Belongs to the terpene synthase family. Not expressed under laboratory conditions.