I am already using proj4j in my project to convert between different coordinate reference systems. (Internally I use WGS84 but some sources supply data in a different CRS.)
Now I need to calculate the distance between two points in meters and am wondering if (and how) that is possible with PROJ4J. (Just in case: my use case is limited to a maximum distance of around 100 km.)
I have come across
org.osgeo.proj4j.util.ProjectionMath#greatCircleDistance(double, double, double, double), but that class is not documented at all. What CRS and unit does that method expect for the latitude/longitude values? And what is the unit for the result?