Preserve Modifier

Preserves, as much as possible, the edge lengths, face angles, and volume of an edited and deformed mesh objectusing an unmodified copy of the object before it was deformed. When you push and pull vertices at the sub-object level, the process typically stretches the edges and often alters the face angles, resulting in irregular topology. You can use the Preserve modifier to generate more regular edge lengths, and a “cleaner” mesh.

Generally, you use the Preserve modifier in this way:

• After creating an object, and before editing it, create a copy.
• Working on the copy, edit it at the sub-object level (pushing and pulling vertices, faces, and so on).
• Apply the Preserve modifier to the copy, click the Pick Original button, and then select the original, unmodified object.
• Adjust the various controls in the Preserve modifier to fine tune the mesh.

Reference

Original: Displays the name of the selected original object. (Note that the so-called “original” object doesn’t actually have to be the original. It’s simply a copy of the object that represents its unmodified topology.)

Pick Original: Click this, and then select an unmodified copy of the current object. Note that the object you pick should be one with the same topology as the current object, and must have the same number of vertices. While you can select a completely different object with equal vertices, the results are unpredictable.

Iterations: Use this to specify the number of calculations toward the solution. The higher this number, the closer the object comes to matching the original objectand the slower the process. When this is set to zero, the original object has no effect, as if the Preserve modifier were never applied.

Preservation Weights Parameters

Edge Lengths,Face Angles,Volumes: Lets you adjust the relative importance of the three components you’re attempting to preserve edge lengths, face angles, and volume. In most cases, you’d leave these at their default settings, but you can achieve some interesting effects by altering them. Higher face angles, for example produce stiffer meshes.

Selection Parameters

Provides options that let you specify which selection level to take from previous selection modifiers in the Stack. The Preserve modifier acts on the specified selection.

Apply to Whole Mesh: When this is checked the other two checkboxes are disabled, and Preserve is applied to the entire object, regardless of the selection passed it from previous levels of the Stack.

Selected Verts Only: When checked, previous sub-object vertex selections are used by Preserve. Note that, it doesn’t matter if Sub-Object/Vertex mode is active in a previous Stack item. As long as vertices have been selected, Preserve will use that selection.

Invert Selection: When checked, the selection passed up the Stack is inverted.

Note: Note that, if all of the checkboxes are unchecked, Preserve uses whatever active selection is passed up the Stack. Thus, if a Mesh Select modifier is set to Sub-Object/Vertex, then that vertex selection is used. If the same Mesh Select Modifier is set to Object level, then the entire object is affected.

How To

Using Preserve on a Sphere

1. Create a GSphere and SHIFT-move to make a copy of it.

Tip: If you want to see the effect of Preserve on mapping, apply a checker-mapped material to the sphere and display it in the viewport s before making the copy.

2. Convert the copy to an editable mesh.
3. At Sub-Object/Vertex level, select about the top third of vertices at the top of the sphere, and move them upward (as seen from the Front) about one radius in distance.

Notice the stretched edges between the moved vertices and the remaining vertices.

4. While still in Vertex sub-object mode, apply the Preserve modifier.
5. Click the Pick Original button, and then select the original (unedited) sphere.

The selected vertices move back toward the sphere in an attempt to maintain the original volume and edge lengths.

6. Check Invert Selection.

The selected vertices return to their moved position, and the unselected vertices (the inverted selection) move up toward the selected vertices.

7. Uncheck Invert Selection.
8. Slowly reduce the Iterations to 0.

The object now looks as it did before Preserve was applied.

9. Increase Iterations to the default 25, and then increase it to approximately 75.

The object is now almost completely spherical again.

10. Set Iterations back to 25, and then try different Edge Lengths, Face Angles, and Volume settings, just to get a feel for their effect. (You can restore the defaults by settings Edge Lengths to 1.0, and Face Angles and Volume to 0.3.

Keep this example, you’ll continue in the next exercise.

Animating a Preserved Object

Of course, you can animate the Preserve parameters, but the following shows you how to use Morph and Preserve together.

1. Remove the Preserve modifier from the copied sphere, and go to Object level (instead of Sub-Object level).
2. With the copied (and deformed) sphere still selected, choose Create/Compound Objects/Morph to make it into a Morph object.
3. Make sure Instance is chosen in the Pick Targets rollout.
4. At frame 0, click Pick Target, and then select the original sphere.
5. In the Modify panel, go to frame 100, select sphere02 in the Morph Targets list, and click Create Morph Key.

The object now morphs from a sphere to a deformed sphere.

6. Apply Preserve to the morph object.
7. Click Pick Original, and select the original sphere.

The object now morphs from the sphere to a preserved and deformed sphere. Note that, because the object selection is passed up the Stack, the Preserve effect is applied to the entire sphere.

8. Choose Selected Verts Only in the Selection area.

Now, only the selected vertices are affected by Preserve. The morph still works, however.

Using the Selection Checkboxes

This exercise provides some examples of how to use the three checkboxes in the Selection area.

1. Reset MAX, create a box, and collapse it into an editable mesh.
2. SHIFT-Move it to make a copy.
3. In the Modify panel, select the top four vertices in the second box and move them upward in Z making the box taller than the original.
4. Apply Preserve, and pick the first box as the original.

The selected vertices move down to match the original edge lengths.

5. Set Iterations to 0 to move the vertices back up, then check Invert Selection, and set iterations back up to 25.

The selected vertices stay in their original locations, but the unselected vertices move upward to restore the original edge lengths.

6. Turn Iterations back down to 0, check Apply to Whole Mesh, and then turn Iterations back up to 25.

Preserve is now applied to the whole mesh. Since all vertices are affected, the top and bottom of the box come together.

7. Go back in the Stack and turn off the Sub-Object button (without changing the selected vertices).
8. Return to Preserve and uncheck Apply to Whole Mesh.

Nothing changes because the whole mesh is already being sent up the Stack.

9. Unclick Invert Selection and click Selected Verts Only.

You’re back to the original effect because, although you turned off Sub-Object selection, the previous vertex selection is still available and can be used by Preserve regardless of the state of the Sub-Object button. You can move the Iterations spinner up and down to see that you’re affecting the selected vertices.

Now, continue with a variation on this:

1. Remove the Preserve modifier from the Stack.
2. SHIFT-Move the second box, making a reference of it.
3. Apply Preserve to the third, reference box, and choose the first box as the original.
4. Select the second box, and go into Sub-Object/Vertex mode.

The third box changes.

5. Select and move a single vertex of the second box.

The third box changes drastically.

6. Go into Sub-Object/Face level.

Again, the third box changes. Here’s how to avoid all of this:

7. Leave Sub-Object mode, and select the third box.
8. Check Apply to Whole Mesh.
9. Select the second box again, go into Sub-Object/Vertex level and move some vertices.

You can now switch sub-object levels without the third box jumping around. Changing vertices on the second box still affects the third box, but it’s not nearly as dramatic.

Cheap Cloth Tricks

The following provides an example of simple cloth simulation method.

1. Reset 3DS MAX, create a Quad Patch Grid, and convert it to an editable mesh.
2. Make a copy, and then make a reference of the copy (as you did with the boxes in the previous example).
3. Apply Preserve to the third patch, using the first as the original.
4. Check Selected Verts Only and check Invert Selection.
5. Set Iterations to 100.
6. Select the second patch, and go to Sub-Object/Vertex level.
7. Select a single vertex in the middle of the patch and move it upward in Z.

The third patch becomes a floating handkerchief.

8. Undo the vertex move.
9. Select the far two corner vertices of the second patch, and drag them upward in Z.

Now, you’ve got the beginnings of a sheet hanging on the line.