NURMS smoothing does its job a little too well. There should be clear joins between some parts of the airplane; for example, between the wings and the fuselage. You can fix this by using smoothing groups. Smoothing groups change the appearance of the model without changing its geometry. Unlike NURMS, smoothing groups don’t increase the face count: This can be an important consideration if you are preparing your model for use in a game.

Set up the lesson:

• Continue working from the previous lesson.

Set up the viewports:

1. With the P-47 selected, choose (Zoom Extents All Selected).
2. Activate the Left viewport, and region zoom to get a good view of the air intake.

   

Smooth the engine cowl:

1. Go to the (Polygon) sub-object level.
2. Press Ctrl+A to select all polygons in the airplane.

   

3. On the ribbon Properties panel drop-down portion, click (SmGroups).

   3ds Max opens the Smoothing Groups dialog.

   

4. On the Smoothing Groups dialog, click Clear All.

   

   This removes any default smoothing-group values that the faces might have.

   Leave the Smoothing Groups dialog open: You will be using it throughout this lesson.

5. On the main toolbar, make sure the Window/Crossing toggle is in its Crossing state, then in the Front viewport, drag a region to select the faces at the very front of the engine cowl.

   

6. On the ribbon Modify Selection panel, click (Grow) a couple of times, until all of the engine cowl is selected.

   

7. On the Smoothing Groups dialog, turn on 32.

   

   3ds Max smooths the faces of the engine cowl.

   The basic idea of the smoothing-group values is simple: If two faces share the same value, 3ds Max smooths between them. If they have distinct values, there is no smoothing. (A face can have more than one smoothing-group value, which complicates matters, but we won’t use that feature in this tutorial.)

Remove smoothing from the air intake:

In this procedure, you don’t really remove smoothing from these faces: You just assign them to a different group from the rest of the cowl.

1. In the Left viewport, click and Ctrl+click to select the faces of the air intake.

   

2. On the Smoothing Groups dialog, click to turn off 32, then turn on 31.

   

   Now the air-intake faces look flat.

   

Smooth the wings:

1. In the Top viewport, drag and Ctrl+drag to select the tips of the wings.

   

2. On the ribbon Modify Selection panel, click (Grow) several times, until all of the wings are selected.

   

   

   Perspective view

3. On the Smoothing Groups dialog, turn on 24.

   

Smooth the horizontal stabilizers:

The steps for the horizontal stabilizers are almost the same as those for the wings.

1. In the Top viewport, drag and Ctrl+drag to select the tips of the stabilizers.

   

2. On the ribbon Modify Selection panel, click (Grow) a few times, until all of the stabilizers are selected.

   

3. On the Smoothing Groups dialog, turn on 23.

   

Smooth the remainder of the fuselage:

Now all of the model is smoothed correctly, except for the main fuselage. You can use the smoothing groups you’ve already created to help select it.

1. On the Smoothing Groups dialog, click Select By SG.

   

   3ds Max opens a Select By Smooth Groups dialog. The buttons show only those smoothing groups that you’ve assigned so far.

   

2. On the Select By Smooth Groups dialog, turn on all four buttons, then click OK.

   

   3ds Max selects those faces that already have a smoothing-group value assigned.

   

3. Press Ctrl+I to invert the selection.

   Now only the fuselage and tail are selected.

   

4. On the Smoothing Groups dialog, turn on 16.

   

   Smoothing the fuselage has an unexpeted effect: The faces around the cockpit are indented too deeply. You can use the Smoothing Groups dialog to fix this.

   

   Unwanted indentation around the cockpit

   (This is easier to see when the polygons are not selected, but you don’t need to deselect the polygons in your scene.)

5. Make sure the fuselage polygons (smoothing group 16) are selected, then on the Smoothing Groups dialog, change the Auto Smooth threshold value to 80.0, and then click Auto Smooth.

   

   3ds Max corrects the indentation around the cockpit.

   

   Increasing the threshold value increases the chance of two faces to be smoothed together.

   NoteAuto Smooth changes the smoothing value (16) that you originally assigned to these faces. After you click AutoSmooth, the faces share values of 1, 2, and 3.

Use smoothing groups with NURMS smoothing:

1. Exit the (Polygon) sub-object level.
2. On the ribbon Edit panel, turn on (NURMS).
3. On the ribbon Use NURMS panel, increase the number of iterations to 2.

   The default NURMS smoothing ignores the smoothing groups, and blends all faces of the P-47 together.

   

4. On the ribbon Use NURMS panel drop-down portion, open the Separate By drop-down list, and turn on Smoothing Groups.

   

   With smoothing groups taken into account, NURMS correctly shows seams between the air intake and the rest of the engine cowl, and between the wings and stabilizers and the main fuselage.

   

5. Turn off (NURMS).

   Although the smoothing provided by smoothing groups alone is not as good as NURMS smoothing, it could work for a low-polygon environment such as a game engine, or for viewing the model in a medium or long shot.

   

Save your work:

• Save the scene as p47_smoothed.max.