Get UTM Zone from GeoTIFF (geotools java)

Question

I've loaded a GeoTiff successfully in with geotools (21-SNAPSHOT), but I'm having trouble accessing the referenced UTM zone.

The code to read in the file is here:

File tiffFile = new File(filePath);
GeoTiffFormat format = new GeoTiffFormat();
Hints hint = new Hints();
hint.put(Hints.FORCE_LONGITUDE_FIRST_AXIS_ORDER, Boolean.TRUE);
tiffReader = format.getReader(tiffFile, hint);
GridCoverage2D grid = tiffReader.read(null);

I'm inspecting the GridCoverage2D object in my debugger and have found the information in a few places.

The information I'm looking for here is the "UTM zone 16N". Perhaps the zone is given in numerical form somewhere else in the object?

This is inside GridCoverage2D->GridGeometry2D->CoordinateReferenceSystem2D

But for the life of me I cannot figure out how to access this information. There's no reference to the underlying transformation conversionFromBase in the top level object. None of the accessible methods get me anywhere closer.

Is there an encoded version somewhere in the CoordinateReferenceSystem metadata?

EDIT

The output of the .toWKT() method on my CoordinateReferenceSystem is below

PROJCS["unnamed", GEOGCS["GCS Name = unknown", DATUM["Datum = unknown", SPHEROID["Ellipsoid = unretrievable - using WGS84", 6378137.0, 298.257223563]], PRIMEM["Greenwich", 0.0], UNIT["degree", 0.017453292519943295], AXIS["Geodetic longitude", EAST], AXIS["Geodetic latitude", NORTH]], PROJECTION["Transverse_Mercator", AUTHORITY["EPSG","9807"]], PARAMETER["central_meridian", -87.0], PARAMETER["latitude_of_origin", 0.0], PARAMETER["scale_factor", 0.9996], PARAMETER["false_easting", 500000.0], PARAMETER["false_northing", 0.0], UNIT["m", 1.0], AXIS["Easting", EAST], AXIS["Northing", NORTH]]

Answer 1

I usually use a block like:

AbstractGridCoverage2DReader reader = format.getReader(file,hints);
GridCoverage2D coverage = reader.read(null);
crs = coverage.getCoordinateReferenceSystem();

But if you are starting with a GridGeometry then it also has a getCoordinateSystem method you can use directly.

EDIT

Querying the internals of a CoordinateReferenceSystem is possible, what you get back tends to reflect what was provided by the input file.

I use crs.getName() which gives me "EPSG:WGS 84 / UTM zone 35S" but for a fuller investigation I used:

if (crs == null) {
  crs = cov.getCoordinateReferenceSystem();

  System.err.println("Set CRS to " + crs.getName());
  Collection<GenericName> alias = crs.getAlias();
  if (alias.isEmpty()) {
    System.err.println("No Alias");
  } else {
  for (Iterator iterator = alias.iterator(); iterator.hasNext();) {
    GenericName genericName = (GenericName) iterator.next();
    System.err.println(genericName);
  }
  }
  Set<ReferenceIdentifier> ids = crs.getIdentifiers();
  if (ids.isEmpty()) {
    System.err.println("No ids");
  } else {
    for (Iterator iterator = ids.iterator(); iterator.hasNext();) {
      ReferenceIdentifier referenceIdentifier = (ReferenceIdentifier) iterator.next();

      System.err.println("id=" + referenceIdentifier);
    }
  }
  System.err.println(crs.toWKT());
}

for a full(ish) output of:

Set CRS to EPSG:WGS 84 / UTM zone 35S
No Alias
id=EPSG:32735
PROJCS["WGS 84 / UTM zone 35S", 
  GEOGCS["WGS 84", 
    DATUM["World Geodetic System 1984", 
      SPHEROID["WGS 84", 6378137.0, 298.257223563, AUTHORITY["EPSG","7030"]], 
      AUTHORITY["EPSG","6326"]], 
    PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]], 
    UNIT["degree", 0.017453292519943295], 
    AXIS["Geodetic longitude", EAST], 
    AXIS["Geodetic latitude", NORTH], 
    AUTHORITY["EPSG","4326"]], 
  PROJECTION["Transverse_Mercator", AUTHORITY["EPSG","9807"]], 
  PARAMETER["central_meridian", 27.0], 
  PARAMETER["latitude_of_origin", 0.0], 
  PARAMETER["scale_factor", 0.9996], 
  PARAMETER["false_easting", 500000.0], 
  PARAMETER["false_northing", 10000000.0], 
  UNIT["m", 1.0], 
  AXIS["Easting", EAST], 
  AXIS["Northing", NORTH], 
  AUTHORITY["EPSG","32735"]]

It can sometimes be worth going back to the EPSG database so

crs = CRS.decode("EPSG:32735");

or whatever your ReferenceIdentifier was used directly may help.