Overview of Copies, Instances, and References

An object can be a copy of another.

Every time you duplicate an object, you choose one of three methods for cloning the original object. For all three methods, the original and clone are identical at the geometry level. Where the methods vary is in the way they handle modifiers (for example, Bend or Twist).

Copy method: Creates a completely separate clone from the original. Modifying one has no effect on the other.

Instance method: Creates a completely interchangeable clone of the original. Modifying an instanced object is the same as modifying the original.

Reference method: Creates a clone dependent on the original up to the point when the object is cloned. Changing parameters for modifiers that were applied to the object before the object was referenced, will change both objects. However, a new modifier can be applied to one of the reference objects, and it will affect only the object to which it is applied.

Depending on the method used to create them, cloned objects are called copies, instances, or references.

The following discussion focuses on how you might use these methods.

Copies

Copies are the most familiar kind of clone object. Copied objects are completely independent of the original object, and therefore analogous to a precise physical copy.

Example of Using Copied Objects

If you modeled a basic head shape and wanted to create a group of individual characters, you would probably make a copy of the basic head shape each time you started a new character. You could then model an individual nose, mouth, and other features.

Instances

Instances are alike not only in geometry, but also in every other way as well.

When you change one instance by applying a modifier, for example, all the other instances change with it.

Within the program, instances derive from the same master object. What you’re doing ("behind the scene") is applying a single modifier to a single master object. In the viewport, what you see as multiple objects are multiple instances of the same definition.

Example of Using Instanced Objects

If you wanted to create a school of swimming fish, you might begin by making many instanced copies of a single fish. You could then animate the swimming motion by applying a Ripple modifier to any fish in the school. The whole school would swim with exactly the same motions.

References

References are based on the original object, as are instances, and can also have their own unique modifiers.

When references are created, a gray line is placed at the top of the modifier stack for all clones. Any modification made below the line is passed on to other references, and to the original object. New modifiers added above the line are not passed on to other references. Changes to the original object are passed on to its references.

This effect is useful for maintaining an original that will affect all its references, while the references themselves can take on individual characteristics.

Example of Using Referenced Objects

In the example of modeling heads, you might want to keep a family resemblance in your characters. You could model basic features on the original, then model specifics on each reference.

At some point, if you wanted to see what your characters would look like as "cone-heads," you could apply a Taper modifier to the original head, and have all the other characters take on the same feature. You could give the original character a very pointed head, then apply a separate Taper to some referenced characters to reduce the point toward normal.

For swimming fish, you might choose to make all members of the school as referenced objects based on a single, original fish. You could still control the swimming motion from the original fish, and also add modifiers to individual fish in the school to vary their behavior.

For more information, see Understanding Object Copies, Instances, and References.