Wrong density for some combination of shapes

[axel-grc]

When adding a new shape, the system evaluates the voxel at the center of the new shape to determine the density difference. This difference is used to calculate how much value is added to the phantom. If a previous shape already occupies the center voxel and has the same density as the new shape, the added density will be 0.
So there is a limitation to the phantom we can create, for example we can't create two spheres with centers close to each others, the center of the second will be in the first one and so the density added will be 0.
The problem appears too when trying to use "union" in the same setup.

[SimonRit]

Thanks for reporting. Let's start by documenting this known limitation of RTK. This is because the density of analytical shapes is additive in RTK and is curretly evaluated at the center indeed.