Chapter 6 - Photogrammetry

Question 1

Photogrammetry

Answer 1

Art & science of making accurate measurements by means of aerial photography

Question 2

Intervalometer

Answer 2

Sets the time between photographs to adjust stereoscopic overlap (endlap) -> in mountainous terrain, up to 80% is sometimes acquired

Question 3

Principal point

Answer 3

exact mark where optical axis of camera was pointing during exposure - drawing a line linking the principal points gives the actual line of flight

Question 4

Scale of aerial photo equation

Answer 4

s = ab/AB
s = f/H -> focal length

Question 5

Height measurement equation based on relief displacement

Answer 5

h/H = d/r

the proportion of radial distortion compared to radius gives the height

Question 6

Height measurement equation based on sun’s rays/ shadow length

Answer 6

tan(a) = h/L
h = Ltan(a)

simple trig.

Question 7

Stereoscopic parallax

Answer 7

change in position of an object with height relative to back

Question 8

Parallactic angle

Answer 8

angle an object makes to two eyes (or photos)

Question 9

eye base

Answer 9

distance between the two eyes (or lenses) - human eyes are between 63 and 69mm - larger gap makes stereoscopic discernment at a distance easier

Question 10

Hyperspectroscopy

Answer 10

Crossing eyes to view two consecutive aerial photos

Question 11

x-parallax

Answer 11

change in x position of an object from one photo to the next - closer objects have larger x parallax. Measuring difference in parallax allows us to make topographic maps

Question 12

parallax equation

Answer 12

ho = (H-h)*dp/(P+dp)
where H-h is altitude of aircraft above ground level
P = absolute stereoscopic parallax at base of object being measured
dp = differential parallax