Tuesday, November 29, 2011

Midterm 2 Marking Comments

The midterms are marked and the grades are in WebCT. Here are some comments on the way I marked them.

I must admit I had to go through these more quickly, so if you are unsure of why you lost marks somewhere because I didn't write much, let me know.  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!

Note: The prof said that as long as you didn’t go over the number of questions allowed for each section I could count all the marks for those questions, even if it takes you over 90. I am hoping this was clear for you during the exam, especially because this wasn't the case for the first one.

Number 1

In 1.1, I want to see specifics, especially what function is applied and what you do with the result of that function (add to the height of vertices). Being too general gets you 2/5. If you didn’t mention what the output of the wave function is doing you lost one mark.

In 1.2, the full formula is:
height = amplitude * sin (wavelength * distanceFromSource + angularFrequency*time + shift)
I am taking off 0.5 each for missing wavelength, angular frequency and shift and 1 for missing the others (amplitude, distance from source, and time). Same amount for missing or incorrect explanations. The height/sin part of the equation is worth 1 mark. If you added any terms that shouldn’t be there, I took off 0.5.

In 1.3, the idea is to find which source a particular wave is closer to – that will be the distance used to compute the vertex height. If you correctly did something that added the heights from the two waves together, we are giving marks (12/15).

Number 2

In 2.2, if you only talked about normals needing a proper transformation when transformations like shear are applied, you got 3/7. I needed to know what happens and why it matters in more detail (normals won’t be perpendicular, lighting will be wrong, etc).

Number 4

Forgetting to discuss 2-3 operations for the shaders will lose you 2 points each for 4.1 and 4.2.

Forgetting to state output for 4.1 and 4.2 loses you 1 mark.

Number 5

In 5.1, half marks are given for a reasonable discussion that shows a misunderstanding of the lighting components.

In 5.3, if you say that vertex shaders can be used to do bump mapping but don’t say how (as in, where are you going to get info on how to modify normals, such as from a texture), I took off 1 mark.

Number 6

In 6.1, getting the wrong R vector results in two marks lost (especially if I can’t see how you computed it).

In 6.3, if you forget the surface material value you lose 1 mark, and if you forget the source light you lose 1 mark. If you don’t normalize V and R you lose 1 mark.

No comments:

Post a Comment