Add SeaFloor Altitude Modes

[devHazz]

As per the Google Dev Reference, Add SeaFloor Altitude Modes

[pjsier]

Thanks for the PR! Could you say a little more about this? It looks like from the documentation you shared that this would only work inside of a namespaced gx:altitudeMode element, and not the base altitudeMode.

I'm seeing support for seaFloorAltitudeMode in the OGC specification here http://docs.opengeospatial.org/is/12-007r2/12-007r2.html#326, but having a better sense of your use case might help

[devHazz]

From what I've seen by attempting to use the lib so far, it throws the correct InvalidAltitudeError so it seems to parse the gx prefix fine? Not sure if that's intentional? I'm using the lib for parsing airspace data from an Air Traffic Service source so it relies heavily on height based on sea floor.

[pjsier]

Got it, thanks for checking that! This might dig into the internals of the quick-xml library, but would it be possible to write out any altitudes with SeaFloor as the altitude with a gx: prefix on altitudeMode? That seems like it could maximize compatibility, even if it results in some inconsistency

[devHazz]

From the data I've been working with, they all utilise the gx: prefix so it seems that compatibility should be more than reasonable

[pjsier]

@devHazz great! Let me know if I can help with looking into that or if there are any broader changes we would have to make

[devHazz]

From more of the testing I've done, it seems my commit is perfectly working and ready for a merge. It seems to be compatible.