Section 2.1 Flashcards
What is the difference between a map and an aerial photo?
Maps use symbols, and aerial photos have real life details
Define Photo Interpretation.
The process of identifying objects or conditions in aerial photographs and determining their meaning or significance.
What are the photo interpretive elements? (8)
Shape Size Tone/colour Texture Pattern Shadows Association/site Time
What is aerial photography?
A form of remote sensing that takes an over head image of the land
What does looking at shape reveal about land use?
Geometric characteristics, can indicate if it is natural or man made.
What can size say about land use?
Comparative volume shows what percentage of land is used for what.
What does tone/colour say about land use?
Shades of grey can show how much light is reflected back from a surface. Colour can indicate where specific wavelengths are stronger.
What does texture reveal about land use.
Texture can indicate what is in the land smooth being water or ice, course being vegetation.
What does shadow indicate about a land use or objects?
Shadow provides information about an objects height, orientation and shape
What does site indicate about land use?
Looking at different locations compared to one another to establish possible relationships
What does time tell us about land use images.
It shows development over time.
What do focal lenses effect?
The angular field of view, meaning you can see more area.
By increasing your angular field of view you can fly at a ______ altitude.
Lower
A wide focal lens means there will be a ________ focal length and a ________ larger angle view.
Shorter, larger.
Which is correct:
Scale = focal length / flying height
Scale = flying height / focal length
Scale = focal length / flying height
Label the variables in this equation.
RF = PD / (MDxMS)
RF = scale PD = photo distance between points MD = map distance between points MS = map-scale denominator
What are fiducial marks?
Registration marks engraved on sides and corners of photographs
Define the principal point.
The exact geometric point in the centre of a photograph found by joint adjacent fiducial marks
What are the 3 types of centres in aerial photographs?
Principal point
Nadir
Isocenter
Define Nadir.
It is a centre point in an aerial photo directly under the focal plane, relief displacement.
Define Isocenter.
Tilt displacement, exactly half the distance between principal point and nadir.
What makes a true vertical photograph?
All three centre points, principal point, nadir and Isocenter, are identical
Label the variables:
VE = 0.076(B/H)(d•/be)s
VE = vertical exaggeration B/H = base to height ratio , distance between two pp on overlapping photo. d•= stereoscopic viewing distance ( viewing distance above the plane of the photo) be= eye base ( distance between the centre of the oculars on the stereoscope) S = photo separation, distance between two photos
Define vertical exaggeration.
Change in proportion of objects appearing in aerial photographs. Causes objects to appear higher and slopes greater than reality
Define relief displacement
The displacement of a 3-D object on a photograph due to changes in height.
Why does relief displacement occur?
3-D images being projected onto 2-D surfaces.
Identify the variables:
d = r(h)/H
d = relief displacement r = distance from principal point h = height of object above surface H = flying height
Define parallax.
The apparent displacement of an object caused by the movement of the observer relative to that object.
Identify the variables:
h = (H)dP/ (Pb+dP)
h = height of object H = flying height dP = parallax difference between top and bottom of an object Pb = absolute parallax of an object base
