How to retrieve the type of CRS (geographic or projected)?

Question

Is there a way with GeoTools to know whether a CRS is geographic (in degrees) or projected (in meter) ?

I have tried empirically with the following code (based on a check of the CRS unit) but I am not sure at all if it is going to work for all CRSs... Is there a better and more correct way ?

public enum CRSType { GEOG, CARTO, UNKNOWN }

private static CRSType getCRSType(Unit<?> unit) {
    if(unit == null) return CRSType.UNKNOWN;
    switch (unit.toString()) {
    case "": return CRSType.UNKNOWN;
    case "°": return CRSType.GEOG;
    case "deg": return CRSType.GEOG;
    case "dms": return CRSType.GEOG;
    case "degree": return CRSType.GEOG;
    case "m": return CRSType.CARTO;
    default:
        LOGGER.warn("Unexpected unit of measure for projection: "+unit);
        return CRSType.UNKNOWN;
    }
}

public static CRSType getCRSType(CoordinateReferenceSystem crs) {
    return getCRSType(CRSUtilities.getUnit(crs.getCoordinateSystem()));
}

Answer 1

I think a more reliable method (since you've overlooked feet and chains to name but two) is to check if your projection is an instance of DefaultGeographicCRS or DefaultProjectedCRS. Theoretically, it could also be a DefaultEngineeringCRS (which I think is neither), a DefaultGeocentricCRS, a DefaultImageCRS (that I've never seen in the wild) or a temporal or vertical CRS (again probably not what you want anyway).

So I came up with the following test code which seems to give the expected answers:

ArrayList<CoordinateReferenceSystem> crsList = new ArrayList<>();
CoordinateReferenceSystem wgs84 = DefaultGeographicCRS.WGS84;
crsList.add(wgs84);
String[] codes = { "4326", "27700", "5243", "5673", "4087", "42309", "26956", "8857" };
for (String code : codes) {
  CoordinateReferenceSystem crs = CRS.decode("EPSG:" + code);
  crsList.add(crs);
}
for (CoordinateReferenceSystem crs : crsList) {
  System.out.println(crs);
  if ((crs instanceof DefaultGeographicCRS))
    System.out.println(crs.getName().getCode() + " is geographic");
  if ((crs instanceof DefaultProjectedCRS))
    System.out.println(crs.getName().getCode() + " is projected");
}

Update

A slightly cleaner method would be to look for org.opengis.referencing.crs.ProjectedCRS and org.opengis.referencing.crs.GeographicCRS