HDR probe (angmap) as environment map?

I’m trying to come up with a way of faking metal effects for animation work, without having to raytrace (too much, anyway…). It doesn’t need to be all that realistic, so I was thinking of using a reflection map for some subtle highlights in addition to speculars. I’d like to use an angular map hdr probe, but there doesn’t seem to be any way to use angular mapping for reflections.

I tried creating an environment map from the middle of the scene with the angular map set to the environment, and use that for the reflections, but the mapping ends up all wrong. All the faces of the cubemap seem to be the same. Only thing I can think of that I haven’t tried yet is somehow converting the angular mapping of the hdr probe to spherical, and mapping it to the inside of a large sphere, then creating an environment map from that.

Any ideas?

Replying to my own question here…

Thankfully the HDR probe I’m using is available as a cube map in addition to the angular one. (Yes, it’s one of Paul Debevec’s…). And thankfully Blender, although not letting you save environment maps in hdri format (it simply won’t do anything when you hit save), it’ll import them properly.

So: it seems my solution is to first figure out the layout of Blender’s cube maps, which seems to be:

Xneg Yneg Xpos
Zneg Zpos Ypos

(Surely this is documented somewhere? If it isn’t, it damn well should be – all over the environment map article in the wiki.)

And then Photochop the HDR cubemap to match this.