As the baseline, the distance between the cameras, increases, what happens to the disparity?
- the disparity decreases
the disparity increases
- the disparity stays the same
- the product of disparity and focal length stays the same
The disparity must increase as the baseline increases. You can easily show this by pointing at something and moving your head from side to side.
When dividing two quantities that have associated errors, which of the following procedures is correct?
When we multiply or divide quantities, we must add their fractional errors.
If the diameter of a circle is measured as (2.0 +/- 0.2) m, what is the percentage error in the circle's circumference?
The percentage error in the measurement is 100 x (0.2 / 2.0) = 10%. As the circumference is given by 2 pi r = pi d (where d is the diameter), the percentage error in the circumference is also 10%. Although pi is an irrational number and hence has an infinite number of decimal places, it is known to >10^9 decimal places which is well beyond the accuracy of any measurement we are likely to make.
Which of the following equations determines the distance to an object $Z$ given its disparity $D$, baseline $B$ and focal length $f$?
- $Z = fD / B$
- $Z = D / fB$
- $Z = B / fD$
$Z = fB / D$
This is an equation that you need to be very familiar with; if you got this wrong, make sure you learn the equation and are able to derive it!
How does disparity vary with distance?
Disparity D and distance Z are related by Z = fB / D so Z is inversely proportional to D.
If the length of the sides of a brick is (20.00 +/- 0.02) cm, the length of two bricks placed side by side is
When we add quantities, we must add their errors.
If the diameter of a sphere is measured as (2.0 +/- 0.2) m, what is the percentage error in the sphere's volume?
The percentage error in the measurement is 100 x (0.2 / 2.0) = 10%. As the volume is given by 4/3 pi r^3 = pi d^3/6 (where d is the diameter), we are calculating the product of three quantities with errors. Hence, their fractional (percentage) errors add, so we have 3 x 10 = 30% error in the volume.
Why is a pin-hole camera rarely used in practice?
Exposure times are long
- The pin-hole is always too large for an image to be made
- Only distant objects are in focus
- Only nearby objects are in focus
A pin-hole lets very little light into the camera, so exposure times are long.
A particular measurement of the height of a building is repeated many times. The mean and standard deviation of the measurements are calculated and found to be (50.0 +/- 0.5) m. Assuming the uncertainties are Gaussian-distributed, which of the following statements is true?
We obtain 95% confidence with 2 standard deviations (SDs) from the mean. As the SD is 0.5 m, 2 x SD = 1 m, and that corresponds to 49--51 m.
Which of the following is usually the most important source of error in computational stereo?
The only item listed which is measured, which means its error can be estimated and accommodated in calculations of distance, is the baseline.