4.8.12. Focal length

Try these first

1. 1.

   Define focal length.

   Hint

   Think about how a lens focuses light.

2. 2.

   What is scale in photogrammetry?

   Hint

   Remember how maps can represent real distances.

3. 3.

   What does the term focal length refer to?

   • Distance to the ground
   • Distance from camera to focal plane
   • Distance in mapping

   Hint

   It's about the lens not the ground.

4. 4.

   True or False: The scale of a photograph taken in flat terrain remains constant.

   • True
   • False

   Hint

   Think about the relationship between height and scale.

5. 5.

   If an aerial camera with a focal length of 150mm is at 2000m, but the ground height is variable between 50m and 100m, calculate the scale at both points.

   Hint

   Use the formula for each elevation point individually.

6. 6.

   Discuss how the scale variance might affect a mapping project in an urban environment with many tall buildings.

   Hint

   Consider the impact of cliffs and valleys in urban settings.