This is a bit confused. Current RT implementations are faster at intersecting the mesh along the ray direction than sphere tracing (which require the expensive lookups or evaluations).
The distance to the surface is independent of direction, it is only a function of position (as all SDFs are).
The depth map is the distance from ray origin to intersection only, not how close that ray came to the surface at any point along it's segment.
The distance to the surface is independent of direction, it is only a function of position (as all SDFs are).
The depth map is the distance from ray origin to intersection only, not how close that ray came to the surface at any point along it's segment.