"Rate of change" units confused with linear/angular/scale units

[desruisseaux]

PROJ C++ API defines an osgeo::proj::common::UnitOfMeasure::Type enumeration with the UNKNOWN, NONE, ANGULAR, LINEAR, SCALE, TIME and PARAMETRIC values. For example the METRE is declared of the LINEAR, which is fine. But the following are more problematic:

• METRE_PER_YEAR declared of type LINEAR
• ARC_SECOND_PER_YEAR declared of type ANGULAR
• PPM_PER_YEAR declared of type SCALE

The consequence is that METRE_PER_YEAR is created by PROJ-JNI as an Unit of type Length while it should be a unit of type Speed. Same apply to other rate of changes unit.

There is no clean fix at this time since PROJ does not provides an API for determining that a unit of measurement is actually a rate of change instead than directly the specified type. A possible workaround could be to parse the unit name.