the logic in polyvox for creating a solid voxel is (density >= threshold) but the logic for a ray cast is (density > threshold)
everywhere else in the code it seems to use >= or < which is fine - it's just doRaycast that's odd - I've changed mine locally and it works now.

I've also heard this concept is changing in future, in which case it probably doesn't matter.

that is only for the default raycast, which is really not very useful imo.
for density volumes it does not return the correct hit position, and for material volumes you usually want more complex hit queries anyway...

usually you will use the raycast with callback class

Yep, this is probably a mistake, though I can't fix it right now as I don't have the Git wesion of PolyVox on this machine. I'll leave this thread open and change it tomorrow.

But yes, as you say this will change in the future and it will be the users responsibility to decide what is solid or empty.

As discussed in this blog post the raycasting functionality has had something of an overhaul. The bug reported here no longer applies because the user has full control over the stopping criteria of the ray via a callback function.