Revit中坐标系类型多而复杂，下面是获取项目基点坐标系的方法，

ElementCategoryFilter siteCategoryfilter = new ElementCategoryFilter(BuiltInCategory.OST_ProjectBasePoint);

FilteredElementCollector collector = new FilteredElementCollector(doc);
IList<Element> siteElements = collector.WherePasses(siteCategoryfilter).ToElements();

Transform totalTransform = null;
foreach (Element ele in siteElements)
{
    //Parameter paramX = ele.ParametersMap.get_Item("E/W");
    Parameter paramX = ele.get_Parameter(BuiltInParameter.BASEPOINT_EASTWEST_PARAM);
    double X = paramX.AsDouble();

    //Parameter paramY = ele.ParametersMap.get_Item("N/S");
    Parameter paramY = ele.get_Parameter(BuiltInParameter.BASEPOINT_NORTHSOUTH_PARAM);
    double Y = paramY.AsDouble();

    Parameter paramElev = ele.get_Parameter(BuiltInParameter.BASEPOINT_ELEVATION_PARAM);
    double Elev = paramElev.AsDouble();

    //Parameter paramAngle = ele.ParametersMap.get_Item("Angle to True North");
    Parameter paramAngle = ele.get_Parameter(BuiltInParameter.BASEPOINT_ANGLETON_PARAM);
    double Angle = paramAngle.AsDouble();

    XYZ projectBasePoint = new XYZ(X, Y, Elev);
    totalTransform = Transform.CreateTranslation(projectBasePoint).Multiply(Transform.CreateRotation(XYZ.BasisZ, Angle));
}