CAP 201a - Computer Animation I

Lesson 4 - Transforms

Objectives:

This lesson reviews moving and rotating objects, and shows some new ways to do it. Objectives important to this lesson:

1. Transforms: basic move and rotate commands
2. Transform gizmos
3. Scale
4. Base points
5. Coordinate systems
6. Snapping and Align tools
7. Cloning - three variations
8. Mirror, array, spacing, clone and align

Concepts:

The lesson begins with a review of some points covered previously.

• When you choose the Select and Move tool, then click an object, you see a transform gizmo that lets you drag the object on the x, y, or z axis, or on a plane defined by any two of those axes
• New point: If you right-click the Select and Move button, you will get a transform dialog box that lets you enter coordinates for the object
• When you select an object and choose the Rotate tool, you see a transform gizmo that lets you rotate on any one of the three axes, rotate freely on any or all axes, or rotate in the creation plane of the selected view
• New point: If you right-click the Rotate tool, you will get a transform dialog box that lets you enter coordinates for the object

The next new point is scaling. There are three tools for changing the scale of an object.

• Select and Uniform scale - allows you change the scale of an object on one dimension, while 3DS Max changes the other two dimensions to match the original proportions
• Select and Non-uniform scale - allows you to scale the object on one or two axes while the third dimension stays the same
• Scale and Squash - allows you to change the scale of an object on one axis, while 3DS Max changes the other two axes to maintain a constant volume for the object (Volume = height times width times depth)

Transform base points are not clearly defined. When you scale or rotate one or more objects, there is always a base point, a point that you rotate around, or a point that does not move when you scale. This point can be set to be one of three points:

• the pivot point of the object(s) selected (default)
• the center of the object(s) selected
• the center of the frame of reference (such as the grid for the viewport in use)

Exercise Notes and Questions

Note: Exercises should be carried out in the classroom. You will not get very much out of them by just reading, nor will you learn what is required by just experimenting on your own. Each exercise is meant to cover specific content that you will be required to know.

Work through the exercises and turn in your answers to all questions below as part of the homework for this assignment.

Exercise 1: This exercise reviews moving, rotating, and cloning existing objects. Students should be able to go through these steps quickly.

More new material follows exercise 1. The lesson tells us that there are eight coordinate systems in 3DS Max. It introduces four of them:

• world - this is an absolute coordinate system that applies to the scene
• view - the coordinate system of the current viewport
• local - coordinates specific to each object
• pick - the coordinate system of another object

The lesson move on to discuss Snaps. This is an odd topic. Autodesk could have called them quanta or détentes. It is easier to understand what snaps are if we look at several examples.

• object snap - objects can be made to snap (align) to lines on a grid or edges of other objects
• angle snap - rotation of objects can be limited to integral multiples of a number of degrees (multiples of an angle). This was demonstrated in exercise 1, when you limited the rotation of a tire object to multiples of five degrees.
• percent snap - scaling an object can be limited to integral multiples of a percentage of the original size
• spinner snap - sets the amount by which all spinner controls are incremented or decremented with one click

Exercise 2: Exercise 2 shows you how to modify the angle snap setting, and shows what effect it has.
Question 1: This exercise also demonstrates using a coordinate system. Which one?

Exercise 3: This exercise shows you a reason to use the Pick coordinate system.
Question 2: Why does the text have you use this system in this case?

The lesson continues with a discussion of the Align tool. This tool can be useful when you want to align two objects (called source and target) in any of four preset ways. The object properties that can be aligned are minimum, center, pivot point, and maximum. These properties can be selected with regard to any axis (or any two, or all three) for each of the objects. For example:

1. Select an object, making it the source.
2. Click the Align button.
3. Click a second object, making it the target.
4. On the Align dialog box, select the axes to use, and the type of alignment for each object. (You could make them align on their maximum values with respect to a given axis, if you want their furthest edges to be at the same point.)

Exercise 4: Exercise 4 allows you to practice using the Align tool. Note: Remember the the first object you select is the source, and the second is the target. When doing this exercise, it is easy to forget this, and think that the settings on the left are for the leftmost object, the right settings are for the rightmost object. Don't make this error.
Question 3: If you are trying to align two objects whose x axes are not in the same plane, how do you compensate?

The text continues with a lesson on cloning objects. Although we have used one choice in the cloning options dialog already, there are three choices in it that produce different results:

• copy - copies of an object are independent of each other and independent of the original object
• instance - instances are linked objects; changing one instance will affect all other linked instances
• reference - reference objects work both ways: you can change the base object (the original one) and affect all the references, or you can change just a reference, affecting none of the other references or the original

Exercise 5: This exercise asks you to create copies, instances, and references of an original object. As you will see, instances and references are not independent objects. If you change your mind, and need to make one independent, apply the Make Unique command (button) to the object.
Question 4: Where in the 3DS Max interface do you find the Make Unique command?

The lesson ends with a short discussion of four other transforms:

• mirror - creates a new object that is a mirror image of the original with respect to a plane you choose
• array - In programming, an array is a series of objects of the same type. 3DS Max lets you create a series of objects that vary in location, rotation, or scale
• spacing - creates a series of objects that are equally spaced along another object
• clone and align - This is one command, not two. It is like a copy and paste command combined with a replace command. You can put simple temporary objects in a scene, then use clone and align to replace all of the temporary objects with clones of a more complex object.