Axis order and axis names
Most Coordinate Reference Systems have an established convention about axis order and names. But in Carmenta Engine, a Crs instance does not store any information about its coordinate axes – order, direction, names, etc. – except that the length unit is part of the projection component.
The reason is that internally, the coordinate system of a Crs instance is always right-handed, with the first axis going grid east and called X, and the second axis going grid north and called Y. (Strictly speaking, it is the components of a Point that are called X and Y (and Z).) This simple convention has been common in the GIS industry.
However, geographers, surveyors and pilots use different conventions. For example, there is a long tradition of giving latitude before longitude. And in many countries, the tradition is to give northing before easting in the national map projection (if so, the northing can be called X and the easting called Y).
Therefore, there are two areas where the simple GIS convention is not good enough.
When you need to comply with the OGC Web Map Service 1.3.0 or similar standards, the axis order should be as the authority says (the authority is usually EPSG).
When you design a user interface for entering or reading coordinates, the axis names and order should be as the user expects (or as EPSG says).
You can browse the EPSG database at https://epsg.org. When you have found your CRS there, you can find the associated "coordinate system" entity with axis information among the CRS details.
Alternatively, if you already know the EPSG code for your CRS instance, you can call static methods on the Crs class to retrieve EPSG information for your instance.
See
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