Hi Brian,

There is no “glass number” in the API.  In the ZPL, this is simply the order of the glass as they appear in the AGF/BGF glass catalog.  If you have multiple catalogs loaded, then the 2nd catalog starts as the n+1 glass number.  C# code to achieve this would be as follows (note that since this isn’t a built-in function and not documented in the Help Files, this is subject to change without warning):

private static int GlassNumber(IOpticalSystem opticalSystem, int surf)
        {
            int result = -1;
            int gnum = 0;

            var tool = opticalSystem.Tools.OpenMaterialsCatalog();
            string[] catalogs = opticalSystem.SystemData.MaterialCatalogs.GetCatalogsInUse();
            for (int i = 0; i < catalogs.Length; i++)
            {
                tool.SelectedCatalog = catalogs[i];
                string[] glasses = tool.GetAllMaterials();

                for (int j = 0; j < glasses.Length; j++)
                {
                    gnum++;
                    if (glasses[j].ToUpper() == opticalSystem.LDE.GetSurfaceAt(surf).Material.ToUpper())
                    {
                        tool.Close();
                        return gnum;
                    }

                }
            }

            tool.Close();
            return result;
        }