private static string CreateSr(string crs)
{
if (crs.StartsWith(ProjectionHelper.EsriStringPrefix)) return "{\"wkt\":\"" + crs.Substring(ProjectionHelper.EsriStringPrefix.Length).Replace("\"", "\\\"") + "\"}";
if (crs.StartsWith(ProjectionHelper.EpsgPrefix)) return ProjectionHelper.ToEpsgCode(crs).ToString();
throw new Exception("crs type not supported");
}