# Opacity issue in graphics3D

I'm trying to show a .obj model in Mathematica, with its bounding box and a couple of spheres representing the bounding box center and the model center.

This is the imported model (tank was previously imported with Import command on a .obj file):

tankPlot =
Graphics3D[{Gray, EdgeForm[None], tank}, Boxed -> True,
BoxStyle -> Directive[Dashed, Orange, Thickness[0.01]],
Lighting -> "Neutral",
ViewPoint -> {2.0293656000931466, 2.2128267128703496,
1.5604721080384572}]


Now I want to add two black spheres and make the model transparent, so I can show the two centers. This is my code:

tankPlot2 = Graphics3D[
{
{
Black,
PointSize[Large],
Sphere[{0.0, 0.0, 0.0}, 0.2],
Sphere[{0.0, 0.0, 2.0}, 0.2]
},
{
Gray,
EdgeForm[None],
Opacity[0.03],
tank
}
},
Boxed -> True,
BoxStyle -> Directive[Dashed, Orange, Thickness[0.01]],
Lighting -> "Neutral",
ViewPoint -> {2.0293656000931466, 2.2128267128703496,
1.5604721080384572},
PlotRange -> Full
]


This is the result:

As you can see, the bottom sphere is not shown properly: some of its parts are hidden by the tank model even if it's transparent.

Is there a way to fix this opacity issue and show the sphere properly?

I'm using Mathematica 12.

• On Windows, I had some opacity problems with graphics primitives due to a reported bug (CASE:4260146) as mentioned here. I was able to workaround in my case by replacing the primitives with ContourPlot3D. The problem appeared to be Windows specific. – Tim Laska Nov 7 '19 at 13:17