Answers

1.a) P_A=(1,1) (+0.5 mark)

P_B=(1/3,2) (+0.5 mark)

P_C=(5/2,1/4) (+0.5 mark)

1.b) There are several transformations. One possible transformation is:

M_BC=Shear(y,1/2)Scale(3/2,1/2)Rot(x,180)Rot(z,-90)Trans(-4/3,-7) (+ 1 mark)

M_BC=[0 -1/2 7/2]

[-3/2 1/4 1/4] (+ 1 mark)

[0 0 1]

2.a) Volume = 1/3 (base area) ( height) = 4/3 (+1 mark)

2.b) Pyramid: faces = 5, vertices = 5, edges = 8 (+1/4 mark)

Cube: faces = 6, vertices = 8, edges = 12 (+1/4 mark)

Relationship = vertices + faces - edges = 2 (+1/2 mark)

2.c)

outward-facing unit normal vectors for each face

ABCD: (0,0,-1)

ABE: (0,-0.707,0.707)

BEC: (0.707,0,0.707)

ECD: (0,0.707,0.707)

AED: (-0.707,0,0.707)

(-0.5 mark for each mistake)

(-1 mark if normal vectors were not unit vectors)

(+2 marks if correct)

outward-facing unit normal vectors for each vertex

A: (-0.65,-0.65,0.38)

B: (0.65,-0.65,0.38)

C: (0.65,0.65,0.38)

D: (-0.65,0.65,0.38)

E: (0,0,1)

(-0.5 mark for each mistake)

(-1 mark if normal vectors are not unit vectors)

(+2 marks if correct)

(+1 mark if vectors are wrong but the way to calculate them is right)

3.

5 cases:

ray: (0,0,0)->(0,0,1), cylinder (0,10,10);(0,-10,10), radius (1). Answer: hit at (0,0,9) (+2 marks)

ray: (0,0,0)->(0,10.6,9.2), cylinder (0,10,10);(0,-10,10), radius (1). Answer: hit at (0,10.7,9.3) (+2 marks)

ray: (0,0,0)->(0,2,1), cylinder (0,10,10);(0,-10,10), radius (1). Answer: no hit (+2 marks)

ray: (0,0,0)->(0,0,1), cylinder (0,5,5);(0,-5,10), radius (1). Answer: hit at (0,0,6.3) (+1 marks)

ray: (0,0,0)->(0,3,1), cylinder (0,5,5);(0,-5,10), radius (1). Answer: no hit (+1 marks)

4.

No because the angles between faces may not be preserved after the perspective projection, or yes if the inverse of the perspective transform is applied prior to the test. (+1 mark)

The edges to be drawn do not change with changes in the camera eye position. (+1 mark)

Pros: By eliminating edges early on the pipeline, computational time is saved over the next phases. (+0.5 mark)

Cons: We could save more time by doing the same procedure in the object space, or we may lose computational time with edges that will be culled/clipped in later stages of the pipeline. (+0.5 mark).

5.a) If fingers are there -> +2 marks

If hierarchy is working -> +1 mark

5.b) If knuckles are drawn as described -> +2 marks

If hierarchy is working -> +1mark

5.c) Several algorithms were accepted. Some examples are:

Detection of vertices inside cube (for all vertices of both cubes).

Detection of edge-plane intersections (for all edges of both cubes).

Detection of plane-plane intersections.

Note: This is supposed to be a general algorithm between 2 cuboids. If it is specific for the program -> -1 mark.

5.d) if top cuboid turns white when there is a collision -> + 3 marks

5.e) if wrist is rotating, and the hierarchy is working, in terms of (X,Y,Z)-> +3 marks.