Hello Thierry
The axis abbreviation is not a reliable way to determine the axis
direction. In particular the x, y and z abbreviations can be for
anything. Often, "x", "y" and "z" just means "the first axis", "the
second axis" and "the third axis" regardless their direction. A more
reliable way is to use the direction. In the test case that you
provided, just replace all getAbbreviation() method calls by
getDirection(). The return value is an AxisDirection object which works
like an enumeration. Some enumeration values are AxisDirection.EAST and
AxisDirection.NORTH.
Note that for polar projections, there is no such thing as "east" or
"north" directions. From the north pole, all directions are oriented
toward south. So the directions are things like "South along 90°
meridian" and "South along 180° meridian". This is one reason why we can
not commit x, y, z abbreviations to particular directions (an other
reason is historical practice long before computer age).
Note also that the unit of measurement is not necessarily metres. It can
also be foot or other units, depending on the CRS. Apache SIS provides
tools for unit conversions if needed (that would be a topic for a
separated email). Generally, each CRS can have its own axis
abbreviations, directions, and units. The axis properties are defined in
the EPSG database to match the national practice of the country that
provides the CRS.
If you need a uniform axis order and units of measurement, an
alternative approach (probably more efficient) would be to insert the
following linebefore CRS.findOperation(sourceCRS, targetCRS):
targetCRS =
AbstractCRS.castOrCopy(targetCRS).forConvention(AxesConvention.NORMALIZED);
Martin
