Gravity Sketch supports both NURBS Spline data and Mesh polygon data. Check below how Gravity Sketch geometry will be exported in different file formats. For more information on exporting check Export Best Practices.
OBJ, FBX (Mesh)
IGES doesn’t contain Mesh data: Volume, Primitives, and OBJ models in the sketch won’t be exported to IGES. IGES exported from Gravity Sketch also keeps original reference curve data such as Revolve axis.