private VerticalCT makeWRFEtaVerticalCoordinateTransform(NetcdfDataset ds, CoordinateSystem cs) {
if ((null == ds.findVariable("PH")) || (null == ds.findVariable("PHB")) ||
(null == ds.findVariable("P")) || (null == ds.findVariable("PB")))
return null;
WRFEtaTransformBuilder builder = new WRFEtaTransformBuilder(cs);
return (VerticalCT) builder.makeCoordinateTransform(ds, null);
}