Hello, been taking a look at "Adam's 2.5D simple features proposal" at the OGR website. Question: Why not adopt the existing ISO SQL/MM part 3 standard ? The SQL/MM standard is an extension to the existing WKB/WKT by OGC. The extensions includes Z and M geometries, and even arcs (CircularString/CompoundCurve etc). regards, Oyvind Idland