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# difference(with:)

Reduces the voxel array to cover only the portion of its volume not covered by another voxel array.

```
func difference(with voxels: MDLVoxelArray)
```

## Parameters

`voxels`

The voxel array to subtract from this voxel array.

## Discussion

After a difference operation, the voxel array contains only those voxels that were present in the original array and not present in the specified array. That is, a difference operation creates a voxel array representing the space where one volume does not overlap another.

Performing a union, intersection, or difference operation clears out shell level information from all voxels in the array. (That is, the w component of every [`MDLVoxelIndex`](/documentation/ModelIO/MDLVoxelIndex) value in the voxel array is reset to 0.)

---

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