CPSC 425 Fitting Data to a Model 20/21 (Term 1) Practice Questions
Multiple Part True/False Questions. For each question, indicate which of the statements, (A)–(D), are true and which are false? Note: Questions may have zero, one or multiple statements that are true.
Question 1 There are advantages to using a hash table rather than an accumulator array to store votes in a Hough transform. Which of the following statements are true and which are false?
(A) It is faster to enter each vote into a hash table.
(B) There are more votes in each bin when the fitted model is present.
(C) Less storage is required since empty bins in a hash table are not represented explicitly.
(D) It is not necessary to predict the maximum range of each parameter in ad- vance in order to determine the array size.
Question 2 Both the Hough transform and RANSAC are techniques for fitting data to a model. Which of the following statements are true? Which are false?
(A) RANSAC performs better than the Hough transform as the number of pa- rameters in the model increases.
(B) The Hough transform performs better than RANSAC as the number of out- liers increases significantly over 50%.
(C) Performance of the Hough transform improves when the points used to fit to the model are more distinctive.
(D) Foraparticulardataset,RANSACfinds,atmost,oneinstanceofthemodel. On the other hand, the Hough transform can find more than one instance, if multiple instances exist.
Short Answer Questions.
Question 3 The title of the Efros and Leung paper that formed the basis for As-
signment 4 is, “Texture synthesis by non-parametric sampling.” 1
(a) In the context of CPSC 425, what does the term non-parametric mean?
(b) In the context of the Efros and Leung paper, is the use of the term non- parametric in the title appropriate? (Briefly justify your answer).
Question 4 Suppose we want to fit a circle to a set of points using RANSAC. Assume that 75% (i.e., 3/4) of the points are outliers. How many random samples of 3 points are needed to detect the circle with 95% probability? (Note: In an exam setting, you wouldn’t need to compute an actual number, but just show how it would be computed if you had a scientific calculator available).