Wednesday, October 26, 2011

Midterm Marking Scheme

I've marked the midterms and posted the grades on WebCT. Hopefully you will receive your papers back in class tomorrow (Oct 27).

Here is how I broke down the marks for most questions (some of the 5 mark questions aren’t listed because they are more straightforward).

If you think your answer deserves more marks or that I missed something in determining the correctness of your answer, send an email that demonstrates this.  If indeed I think you deserve more marks, I’ll ask you to bring in your midterm paper.

Be sure to check my addition!

Number 1
·         2 for the projection role
·         2.5 for the defining parameters (0.5 each)
·         2.5 for the diagram
·         1 for what defining parameters form
·         2 for implication on visualizing game objects

Number 2
·         4 for explaining what homogeneous coordinates are
o   3 if correct but not quite enough detail
·         4 for explaining the motivation for them
·         2 for giving example of where they are used
o   1 if you give a correct example but offer an incorrect reason

Number 3
·         For general matrices, 1.5 each for the two translation matrices and 2 for the rotation
·         5 marks for the second part: 1 mark for each of four matrices (including the point) and 1 one mark for the correct order

Number 4
·         15 for describing the steps properly
o   4 for defining two vectors using the triangle points
o   3 for finding the normal via the cross product of these two vectors
o   4 for defining a vector from the triangle to the viewpoint
o   4 for computing the cosine of the angle between normal and vector to the viewpoint (only the sign matters)
·         5 for drawing an accurate picture
o   2.5 if the overall idea is there but it does not generalize well and/or does not show U, V, W, P, or other parts of the computation in the first part
o   2 if the diagram is good but based on wrong method
·         5 for correctly computing whether T is visible from P

Number 5
·         5 for saying why the transformation computes Z-values
o   1 if you mention removing shapes outside view frustum (this will happen before the projection transformation)
·         10 for correct computation
o   7 if correct but not enough math shown to show full understanding
o   9 if there’s a small error
o   7 if you don’t properly multiply the homogeneous coordinate of the point with the value in position (4,3) in the matrix to end up getting zero in the result
Number 6
·         5 for computing orientation
·         7 for computing avatar position
o   5 if you don’t show enough math
o   4 if you don’t normalize the orientation vector and multiply that by 50 units
·         8 for  avatar’s position and orientation
o   7 if you did not do the math and/or there are small errors
o   4 if the method is wrong
Number 8
·         2.5/5 for saying the objects occupy the same space and to pick just one (without saying how)
·         3.5/5 for saying the objects occupy the same space and to change their z-value

Number 9
·         3/5 for saying the object is outside the “render distance”

Number 10
·         3 for explaining the purpose
·         2 for the example
o   1.5 if example is good but based on incorrect understanding of part 1

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