Teacher’s Notes: Digital Image Sources

1
Teachers Notes Digital Image Sources

• Digital images from space can be found at the
  following NASA web site
• http//eol.jsc.nasa.gov/sseop/clickmap/
• Click the map for images of that area.
• You can include in your search results
  information such as Altitude and Focal Length of
  the camera used by selecting FCLT and ALT at the
  bottom of the page.
• Images can be used freely if attributed to NASA.
• For added impact Google Earth (http//earth.google
  .com/) can be used to zoom from space to Tower
  Bridge, the Channel, etc.
• Depending on your location you may find better
  resolution images of your town on Microsofts
  Live Local site http//local.live.com/
• Information on aerial photography
  http//landmap.ac.uk/ipc/ccrs/chapter2/chapter2_7_
  e.html

2
Starter

• How many,
• mm in 20 cm?
• cm in 3.75 m?
• m in 2.5 km?
• cm in 6 km?
• mm in 8 km?

3
Similar Triangles Photography
4
Reminder
25 cm
8 cm
10 cm
x cm
Find the value of x.
Enlargement Factor
x
5
Exercise
In each case, the pair of triangles are similar.
Equal angles are marked. Find i the relevant
scale factor (enlargement or reduction) ii the
missing length.
b
a
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How a Lens Works
Lens
Object Height
Image Height
Distance to object
Focal Length
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Example
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Enlargement Factor
x
x 4000 mm
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Satellite Photography
Image NASA
10
Similar Triangles in Space
Image size
Focal length of camera
Lens
Height above ground (Altitude)
Object size
11
Example
90 mm
20 mm
EF
Lens
135 km
x
x 30 000 000 mm
x
12
Invergordon Academy Playing Fields Aerial
Photo Altitude 400 m Focal length 152 mm
13
Tower Bridge London Aerial Photo Altitude
2500 ft (762 m) Focal length 152 mm
Calculate the span of the bridge.
14
Calculate the shortest distance across the
Channel. (marked)
Image NASA
English Channel Photo taken onboard Space
Shuttle
Altitude 126 miles (203 km) Focal length 90
mm
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Actual Distances

• Tower Bridge 244 m
• English Channel 20 miles or 32 km