Virtual Reality

Front 1

Suppose you are a virtual artist that has to sculpt a virtual cylinder using a Phantom interface.How will you make sure that the cylinder is fully visible and centered in both the visual scene and the haptic space. 6 points

Back 1

The virtual camera has to properly be mapped to the Phantom workspace. First a rotation transformation needs to be applied such that the view axis of the camera is perpendicular to the width of the Phantom workspace. Then the camera origin is moved to the center of the Phantom workspace. Finally the camera is translated by an offset in the negative z axis, such that the whole workspace is visible.

Front 2

How will you make sure that this scaling does not influence the compliance and damping of thevirtual cylinder? 7 points

Back 2

Scaling is needed such that the width of the Phantom workspace is within the viewing cone of the camera. The scaling factor depends on the distance from the camera focal point to the frustrum Dxmax and the distance from the non-scaled Phantom workspace to the side limit Dphantomxmax. The scaling factor is Sfrustum = Dxmax/Dphantommax. Complience and damping (i.e. the haptic properties of virtual interactions) need to be scaled too, so to maintain haptic fidelity.

Front 3

How will you make sure that this scaling does not influence the compliance and damping of thevirtual cylinder? 7 points

Back 3

The scaling coefficient for compliance of the gstShape node becomes SurfaceKspring new = SurfaceKspring current/Sfrustrum and the scaling coefficient for damping becomes SurfaceKdamping new = SurfaceKdamping current/Sfrustrum

Front 4

Now assume that you use FreeForm to create a prototype of a cylinder for marketing purposes.How will you create the cylinder using FreeForm? Draw and explain. How will this cylinder be able to be made of Aluminum? 6 points

Back 4

FreForm is an application for the Phantom which allows the sculpting of digital clay withappropriate haptic feedback. To create a cylinder prototype you would first draw a circle on the cutting plane. Subsequently the outside wire cut button on the FreeFormand the wire cut would leave the cylinder and remove the other clay.The FreeForm file can be exported to a CAM machine for machining out of Aluminum.

Front 5

You conduct a human-factors study with apprentice sculptors and experienced ones. Thevariable measured is the speed of sculpting the cylinder and the dimensional accuracy. If each group performs 3 trials, draw and explain how their performance will vary between trials? (one graph for each variable). 7 points

Back 5

Both groups (apprentice and expert sculptors) will learn with repeated trials. The apprentices willlearn less uniformly, such that their standard deviation of the variable measured will be larger. Learning for the apprentice will be of the task, while the experienced sculptors will learn the system. Their learning will be more uniform, such that their standard deviation will be smaller than that of the apprentice sculptors.

Front 6

Now suppose that the cylinder has a company logo etched in it (ridges). It is now placed in ascience museum where it is shown on a laptop. Visitors are supposed to feel its ridges using a simple mouse. How would you realize that? Draw and explain. 6 points

Back 6

Providing haptic feedback with a non-haptic interface such as a simple mouse has to do with sensorial illusion. Let us not forget that vision is the dominant channel, that it can overpower the proprioceptive (sensing own body motion) and haptic channels. In this problem we want to make visitors perceive the resistance the mouse arrow has when crossing the ridges on the cylinder surface. To do so the speed of the mouse arrow gain has to be decoupled from that of the actual mouse.

Front 7

Now suppose that the cylinder has a company logo etched in it (ridges). It is now placed in a science museum where it is shown on a laptop. Visitors are supposed to feel its ridges using a simple mouse. How would you realize that? Draw and explain. 6 points

Back 7

When approaching a bump/slope, the arrow will be slowed down, while on the other side of the slope it will be accelerated. In the example below, the arrow hits the edge of the lemon slice and slows down, but then accelerates when passing that ridge (other examples acceptable).

Front 8

There was a bug in the software at the museum and the movement of the mouse arrow is offsetfrom that of the mouse itself. The arrow moves much more on the screen than the actual mouse moves. What do you think would happen with visitors that play a lot with this exhibit? Is there an antidote? 6 points

Back 8

Visitors who play a lot with the cylinder exhibit will be subject to a neural conflict between theproprioceptive sensors measuring the hand movement (that of the mouse) and the visual channel showing the movement of the arrow on the screen. With repeated play the visitors will adapt, and move their hand very slowly. The antidote for this adaptation is to remove the neural conflict (either by fixing the bug, or by providing visitors the opportunity to play with mouse that properly maps hand movement to the movement of the arrow on the careen.

Front 9

You design a game of Towers of Hanoi to be played with the Hydra. What are the rules of thegame and how will the Hydra be used to manipulate the disks? Assume there is a hand avatar in the scene controlled by the user’s index. Draw and explain. 5 points

Back 9

Towers of Hanoi game requires the restacking of a number of disks of different diameters from onpole to another, while using the third pole as a way-point. The rule of the game is that at no time can a larger diameter disk be placed on top of a smaller one. This condition dictates an optimal sequence of moves (minimal number of moves) to complete the restacking. The larger the number of disks the more difficult the game.

Front 10

You design a game of Towers of Hanoi to be played with the Hydra. What are the rules of the game and how will the Hydra be used to manipulate the disks? Assume there is a hand avatar in the scene controlled by the user’s index. Draw and explain. 5 points

Back 10

The hand avatar is mapped to the Hydra movement in 3D, while the Hydra trigger controls the amount of flexing/extending of the avatar fingers. To pick up disks the player has to bring the hand avatar in the vicinity of a disk and (upon collision detection) press the trigger to pick up a disk.Placing that disk on another entails collision detection as well. The game can be played with oneHydra pendant or with both (in that case two hand avatars will be in the scene).