parseGpsTuple's validated result: parsed numbers plus the original, untouched substrings for verbatim-as-typed storage.
Optional
The original (trimmed) substrings, for verbatim storage. altitudeType here is already canonical-cased since it is a closed enum, not a freeform/numeric value.
altitudeType
parseGpsTuple's validated result: parsed numbers plus the original, untouched substrings for verbatim-as-typed storage.