How to convert from MSL to height above ellipsoid?

Just like the title says. My data has the altitude above MSL, but I want to convert it for use with Cartesian3 so I need the height above the ellipsoid at the given lat/lon and altitude above MSL. I’m looking through the docs but I don’t see a function for this. Am I just missing it, or how would I go about doing this conversion?

You could try this depending on where you’re trying to do this (client or server), but it will give you an idea of how to do the conversion.