These are two stamp images, the fence above the deer in the layer manager. Neither is z-merged at the moment, and if you want the deer behind the fence like this, or completely in front of it, you would not use z-merge. But suppose you want to show the deer coming through the fence? That is when z-merge comes into its own.

But we cannot get that effect as the two images stand. The deer has no depth. Whatever z-elevation we give it, either the whole deer will be behind the fence, in front of it, or embedded in the fence in such a way that it looks as though the fence posts are semi-transparent and you can see bits of the deer through them.

Before we can put the deer's head through the fence, leaving the rest of its body either between the posts or behind them, we have to give the deer some 3d depth so that its head is going to be nearer to the eye in z-merge space, and its tail nearer to the canvas.

We need to use the virtual trackball, and that that only works with path objects. The deer is an image object at the moment, so select it, by clicking on its thumbnail in the layer manager, and then in the object menu, convert it to a path image, using the option you see in this illustration.

To access the virtual trackball, first click the deformation tool, and then the transform tool.

You will now see the virtual trackball at the bottom of the list of transform tools. Select it. The deer will be surrounded by a circle and the cursor will have a sphere with curved arrows attached to it (which I cannot capture in these screen shots). Move the cursor till it is as near to the centre of the circle as you can get it, WITHOUT IT BECOMING A MOVER TOOL. You want to rotate the deer, not move it.

When you left click with the cursor with its trackball showing, the circle surrounding the deer will change to a rectangle. Holding down the left button, gently move the cursor a little to the left till it becomes shaped like this one. Try not to move it up or down at the same time, or the deer will start leaning backwards, forwards or sideways. All you want to do is swivel it a little bit to give the deer some perspective and depth.

Unlike the z-merge tool, the virtual trackball makes the object look as though its front is nearer to your eye than its back. It resizes the object as part of the rotating process.

If you find you have gone wildly wrong, then use the undo arrow and try again. It is quite hard to recover from a wrong rotation, and much easier to start from scratch. Don't undo as far as the conversion to a path image, or you will find the trackball is greyed out when you try again.

When you have rotated the deer, change to the z-merge tool. Select the fence and check the z-merge box. I left the z-elevation at 0. Now select the deer, and check z-merge for it too. You will probably find that the deer's head pops through the fence without your needing to change the z-elevation from 0, but if it is not quite to your liking, by all means experiment with other z-elevation values. You will probably not need more than -1 or 1 for either deer or fence. The deer has very little depth even after it has been rotated with the trackball, and the fence has hardly any depth at all.

This exercise has introduced the concept of giving a 2d object sufficient depth to enable z-merge to let it interact with another object. The virtual trackball gives some 3d perspective to any 2d path image. Use it carefully, because it is very easy to rotate too vigourously and make your image look grotesque.

The shiny green ring was a circular 3d pipe object, but it has been rotated with the trackball and now has sufficient depth to allow both the sphere and the gold ellipse to sit inside it. The give-away is the way the green ring gets thinner as it goes away from you. It has 3d perspective. The gold ellipse does not. 3d path objects have some depth by their nature, but often not nearly enough to intertwine them unless you give them a little help with the trackball.

The 3d trackball is a very important aid when you are trying to z-merge objects. If they will only go in front or behind other objects, but not inside them, then try using the trackball to give more depth to one or more of your objects.

Move on now to look at making a complex object by z-merging objects so that they go through each other and poke out of each other.