Lecture 2 (second half)

Question 1

What is Cartographic Scale

Answer 1

The ratio between the distance on the photo and the corresponding distance on the ground
- expressed as a representative factor (RF)
written as a ratio X/Y
x= numerator-photo
y=denominator-ground

Question 2

3 Scale determination methods

Answer 2

• focal length & altitude
• photo-map distance
• ground distance

Question 3

What is a large vs small cartographic scale

Answer 3

• The large scale map covers smaller area but generally more detail (denominator is smaller)
• The small-scale map covers larger area with less detail (denominator is higher)
• map scale: the proportion of a distance on a map to the corresponding distance on the ground.

Question 4

Small vs large geographic scale

Answer 4

Observation scale: spatial extent of a study area
- a large geographic scale involves a large spatial area
- small geographic scale study only contains a small spatial area

Question 5

What is Focal length?

Answer 5

distance from the middle of the camera lens to the focal plane (film)

Question 6

What happens to image distortion as focal length increases?

Answer 6

As focal length increases image distortion decreases

Question 7

What is Altitude

Answer 7

linear distance from the center of lens to the ground

Question 8

How to calculate scale from focal length & altitude

Answer 8

• vertical photograph scale is a function of the focal length of the camera (F) and the height above the terrain (H)

RF= F (focal length)/H (altitude).
= average or nominal scale of the photograph

Question 9

How to determine scale from photo-map distance?

Answer 9

RF= 1/ (md)(MS)/PD

Md= map distance btw 2 points
MS= map-scale representative fraction
PD+ photo distance btw the same 2 points
presented as a fraction1/- OR ratio 1: -

Question 10

Scale determination from photo-ground distance

Answer 10

RF= 1/ (GD/PD)

GD= ground distance between 2 points
PD= photographic distance between 2 points

Question 11

Area Determination

Answer 11

• Analog Air Photo = scanner
• Digital Air Photo = digital image processing system
• Image rectification (geometric) = on screen digitalization = perimeter & area

Question 12

Mission Planning 8 Considerations

Answer 12

• Study Area
• Required weather & timing
• Film-filter combination
• film tilting
• flight lines
• Overlap/side lap
• airplane altitude
• flight-plan map

Question 13

Study Area (planning)

Answer 13

• delineation of area to be photographed
• What is the study area- flight altiude
• digital imagery more flexible

Question 14

Required weather (planning)

Answer 14

Wind: plane drifts off course
Clouds: less than 10% cloud cover (shadows)
Season: how much sun, what features of nature must be identified?
- topographic mapping, soils: cant have snow
- vegetation: mid spring to summer= leaves
- submersed features: water turbidity, marshes, flooding

Question 15

Required time of day (planning missiokn)

Answer 15

sun elevation angle= f
- depends on latitude, season, time of day
- shadow is NOT wanted: 30-50 degrees
- shadow is wanted: <30 degrees sun elevation angle
sunspots: occur at high sun elevation angles
- straight line from sun passes through camera lens and intersects ground inside camera)

Question 16

Film=filter Combination (planning)

Answer 16

B & W: cheapest
Color: natural= regular OR color infrared (false color)= more expensive

Filter: subtraction of light (filters out certain colors)
- light is filtered to obtain a narrow amount
- Film filter combination: removes atmospheric haze

Question 17

Flight Lines (planning)

Answer 17

• parallel to the longest axis of study area
• extra flight line added to each side of study area
  Overlap: 60% along flight line (stereoscopic)
  Side lap: 20-30%between adjacent flightlines