I'm trying to use the H15 baking workflow for the first time, and it doesn't seem to work too well… I'm not sure if it's something I'm doing wrong, or if there's something broken. I'm attempting to use a slightly modified version of what's in the help documentation example file.

Maybe someone else has had luck with it and can shed some light on what I might be doing wrong?

Attached is a zip file with the modified example file.

As you can see from the attached image, the tangent normals are not rendering correctly and result in some areas being inverted, and others with clear seams.

Hey Allegro, without looking at your file (I cannot right now) I may be able to take a stab at answering a few questions:

a- The reason the base normal may look smooth could be due to the fact that the mesh that you are using as the hi res mesh is, indeed, smooth as well. Since you are generating a tangent space normal map, it is not storing the differences in between samples in world space, but instead trying to bend the tangents and bitangents to mimic the shading of your sphere. Did you make the hi res sphere by just smoothing your low res sphere?

b - The reason yoy may have seams could be because your UVs have seams in that area. In polygonal meshes, the bake texture default behaviour is to generate tangents and bitangents based on your UV attribute. Although you have seams in the textures, those seams may not be present on your shaded mesh as they are meant to make up for a discontinuity in your tangent basis (i.e. imagine if you had a tshirt which was unwrapped at the side seam, and laid so that the top of the UVs are the back, and the bottom of the UVs are the front. This would cause a seam in your tangent basis which should be present in your normal map)

Have you looked at this with the principle shader to see the result?