Function Ellipsoid.isValid

True when this value represents a supported spherical or oblate ellipsoid.

bool isValid() const pure nothrow @nogc @property @safe;

In particular, Ellipsoid!T.init.isValid is false.

Example

Example checking whether an ellipsoid was explicitly constructed. 

import geodesy;
assert(wgs84!double().isValid);
assert(!Ellipsoid!double.init.isValid);