As a Flash engine, Sandy3D has some limitations. To obtain a good ratio between performance and rendering quality, we have done some choices.

Our Z-sorting approach is one of these choices. We currently use a mean algorithm. We also propose to use an object based sorting or a polygon based one. Both have their pros and cons:

Object based sorting pros:

• performance
• each object has its own container, so very easy to add some filters to its shape, or different effects

Object based sorting cons:

• impossible to have an object intersection
• object sorting is quite bad

The polygon based approach has the opposite pros and cons.

Each object/polygon computes its transformed Z value mean, and we sort the objects/polygons that way.

As a consequence, large objects/polygons do not have a very representative mean value, and they are very often source of sorting issue in Sandy3D.

First if you have objects closed to each others, set their properties useSingleContainer to false. For these objects, the sorting algorithm will be polygon based, hence more accurate.

myObject.useSingleContainer = false;

More generally, the simplest way to solve this, is to make polygons smaller, basically doable increasing the polygon count. Augment the quality, and you'll reduce the sorting artifact.

When using custom models, the effort shall be done at modelisation time.

Yes, Sandy3D offers that possibiliy. You can force the depth of an object.
But before using this feature, be sure to not have a free camera. The forced depth is efficient when the camera does not move in more than 2 dimensions.

This feature is convenient to make a long floor, for example, when you know that the camera will never go beneath:

myFloor.enableForcedDepth = true;
myFloor.forcedDepth = 9999999999999;