Vertical/azimuthal perspective?

[ejschoen]

Not sure where the right place to ask this is. SInce the ol-maplibre-layer exists at the intersecton of MapLibre and OpenLayers, I thought I would start here.

MapLibre GL JS can now render tile data with vertical/azimuthal perspective by setting the projection type to vertical-perspective or can interpolate between web mercator and vertical perspective by setting the projection type to "globe."

proj4 can handle orthographic projections:

+proj=ortho +lat_0=0 +lon_0=0 +x_0=0 +y_0=0 +a=6370997 +b=6370997 +units=m +no_defs 

Rendering a vector layer atop a MapLibre map almost works with the OpenLayers view projection set to the above proj4 definition. Well, only if the camera is positioned above long,lat=0,0:

It doesn't work elsewhere:

I realize the proj4 definition above might have the wrong parameters, but looking at MapLibre's source code, the vertical perspective transform code looks pretty complicated (cf: clipping logic at the limb of the globe) and may not be as simple as can be handled by a proj4 transform. Has anyone explored whether there is a view perspective that can work with OpenLayers to render vector data in a matching vertical perspective?