These raycasting images have been created by a tool created from vesuvius-gui by using alpha blending
to cast rays towards the surface. The surfaces are partly covered by the surrounding teflon sheet 
that was left-over after masking the volume (might be fixed in a later masking run).

To map these images to the volume, image uv coordinates directly map to x/z coordinates of the volume.
Rays were cast from the below y_max in negative y direction.

These were the crop regions:

4um 500P2
let y_range = 3623..6450;

let x_range = 1346..8342;
let z_range = 1753..14556;

2um
let y_range = 7012..12414;

let x_range = 2572..16149;
let z_range = 1405..27501;

E.g. for 4um

point 100 / 200 in the image corresponds to volume coordinates

x = x_min + 100 = 1346 + 100 = 1446
z = z_min + 200 = 1753 + 200 = 1953

Ray was cast from 6450 downwards towards the surface (did not specifically record the median or
threshold or opacity value y value explicitly).