## Objects in 3D Space

Published April 23, 2007
By Richard G. Baldwin

File: Alice0110PracticeTest.htm

## Questions

1.  Which item does not belong in the following list?  Every Alice object has a viewpoint.  The viewpoint of an object is determined by:

• A.  The position of the object in 3D space.
• B.  The width of the object.
• C.  The orientation of the object relative to a 3D coordinate system.

2.  True or False:  Every Alice object has a center point and three axes.

3.  True or False:  The center point is the position in space (relative to the object) at which that object's three coordinate axes cross.

4.  True or False:  The center point of an object is always physically inside the object.

5.  True or False:  If you move an Alice object, you are actually moving its center point.  The rest of the object comes along for the ride.

6.  True or False:  It is not possible to break the connection between an object and its component parts.  For example, you could not cause a Coach object to move away and leave his arms behind.

7.  True or False:  If you turn an Alice object to the right or to the left, you are rotating the object around its blue axis.

8.  True or False:  If you turn an Alice object forward or backward, you are rotating the object around its red axis.

9.  If you roll an Alice object to the right or the left, you are rotating the object around which axis?

• A.  red
• B.  green
• C.  blue
• D.  none of the above

10.  True or False:  When you rotate an object around one of its axes, that axis remains stationary and the other two axes do the rotation.

11.  True or False:  The terms move, turn, and roll are simply jargon that are used to describe certain kinds of motion in Alice.

12.  True or False:  A 3D coordinate system is typically thought of as consisting of three axes where the angle between any pair of axes is forty-five (45) degrees.

13.  True or False:  In mathematical terminology, the axes in a 3D coordinate system are orthogonal.

14.  True or False:  Scientists and engineers typically think of the three axes in a 3D coordinate system as the horizontal axis (often called X), the vertical axis (often called Y), and a third axis that is perpendicular to the plane formed by X and Y (often called Z).

15.  True or False:  Alice doesn't deal with X, Y, and Z axes.  Rather, Alice deals with one axis that runs from left to right, a second axis that runs from bottom to top, and a third axis that runs from front to back.

16.  In Alice, what is the color of the axis that protrudes out in front of an object?

• A.  red
• B.  green
• C.  blue

17.  In Alice, what is the color of the axis that protrudes out to the right of an object?

• A.  red
• B.  green
• C.  blue

18.  In Alice, what is the color of the axis that protrudes out from the top of an object?

• A.  red
• B.  green
• C.  blue

19True or False:  When discussing the colors of the coordinate axes in Alice, the directions front/back, right/left, and up/down are relative to the viewpoint of the object, and not relative to the viewpoint of you the viewer.

20True or False:  Every object in the gallery has a center point, which is the origin where the three axes join with respect to that object's viewpoint.

21True or False:  The center point for a penguin is at a point in space on the ground midway between the penguin's feet.

22True or False:  Many gallery objects are made up of component parts.

23.  Which item does not belong in the following list?  A penguin object is made up of the following smaller component objects:

• B.  right leg
• C.  right hand
• D.  left leg
• E.  right wing
• F.  left wing

24True or False:  Each component object belonging to an object may itself be composed of even small component objects.

25True or False:  The component objects that make up a larger object do not have their own center points and axes.

26True or False:  In order to cause a penguin to flap a wing, we must know the position of the wing object's center point, but we do not need to know the directions of the red, green, and blue axes that go through the center point for that wing.

27True or False:  Given the Alice convention for color-coding the three axes, we would normally expect the red axis to protrude from the top of the cockpit for an airplane object.

28.  Which item does not belong in the following list?

• A.  yaw
• B.  turn
• C.  pitch
• D.  roll

29True or False:  The combination of all possible rotational motions and all possible translational motions results in what is often called eight degrees of freedom.

30True or False:  Because the ground represents terra firma in an Alice world, it cannot be turned or rotated.

31True or False:  When an object's opacity is set to 100%, it is totally transparent.

32True or False:  Every object has a center point and has its own set of 3D axes. The center point and the 3D axes belonging to an object travel with and rotate with the object, independently of the other objects in the world.

33True or False:  If you add a Coach object to your world and immediately turn his left arm to the LEFT by 90 degrees, that will place the arm in a position that most people would consider to be comfortable.

34True or False:  If you add a Coach object to your world and immediately roll his left arm to the RIGHT by 80 degrees, that will place the arm in a position that most people would consider to be comfortable.

35True or False:  If you add a Coach object to your world and immediately roll his left arm to the LEFT by 45 degrees, that will place the arm in a position that most people would consider to be comfortable.

36True or False:  If you add a Coach object to your world and immediately turn his left arm BACKWARD by 140 degrees, that will place the arm in a position that most people would consider to be comfortable.

37True or False:  If you add a Coach object to your world and immediately turn his left arm to the RIGHT by 90 degrees, that will place the arm in a position that most people would consider to be comfortable.

38True or False:  The center point for a Coach object's left arm is approximately half way between his left shoulder and his left wrist.

Copyright 2007, Richard G. Baldwin.  Faculty and staff of public and private non-profit educational institutions are granted a license to reproduce and to use this material for purposes consistent with the teaching process.  This license does not extend to commercial ventures.  Otherwise, reproduction in whole or in part in any form or medium without express written permission from Richard Baldwin is prohibited.

The following image is the splash screen from Alice 2.0, and is the property of the developers of Alice at Carnegie Mellon.

False.

True.

True.

True.

True.

False.

True.

False.

False.

False.

B.  turn

False.

False.

False.

True.

C.  right hand

True.

True.

True.

True.

### Explanation 19

Back to Question 19

B.  green

A.  red

C.  blue

### Explanation 16

Back to Question 16

True.

True.

True.

False.

False.

True.

C.  blue

True.

False.

False.

True.

False.

True.

True.