$5$ The Matlab function imtool$()$ allows us to display an image and perform a

number of different interactive operations upon it$.$ Use this function to load the example

image shown in Figure $2\mathrm{.}16($available as railway.png$)$ and measure the length in pixels of

the railway sleepers in the foreground $($front$)$ and background $($rear$)$ of the image. Based on

the discussion of Section $2\mathrm{.}3\mathrm{.}1,$ what can we determine about the relative distance of the two

sleepers you have measured to the camera? If we assume the standard length of a railway

EXERCISES $47$

sleeper is $2\mathrm{.}5$ m$,$ what additional information would be need to determine the absolute

distance of these items from the camera? How could this be applied to other areas, such as

estimating the distance of people or cars from the camera?