Photogrammetry Midterm

Vertical/Nadir

Photo taken from above

Low Oblique

Photo taken from an angle

High Oblique Photo

taken from a high angle, you can see the horizon

Photogrammetry

art, science, and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring, and interpreting photographic images and patterns of recorded radiant electromagnetic energy and other phenomena.

Dr. Carl Pulfrich

overlapping pairs of photos (1909)

formed foundation for many instrumental mapping techniques used today

Colonel Aime Laussedat

“Father of Photogrammetry”

topographic mapping with photos from a ballon/kite (1859)

Forms of Photogrammetry

terrestrial - from the earth

aerial - from the air

metric - looking for measurements

interpretative - looking to see whats going on

Uses of Photogrammetry

•Topographic maps•Orthophotos (orthomosaics)

•Digital elevation/surface models

•Surveying and highway planning

•Making models (teeth, buildings, shipwrecks)

Why not use high oblique photos?

its hard to stitch together images due to the lack of reference points

Why not use NADIR photos

Nadir photos don’t capture much depth

General Rule for Overlap

60% going front to back

30% when going side to side

Spatial Resolution

how big is the pixel and height of the flight

(the higher you are, the more area covered by 1 pixel)

(Higher you are, lower the spatial resolution)

Temporal Resolution

how often is the same scene imaged? How often do I need to image the scene to accomplish my goal?

Spectral Resolution

 black and white vs color

Radiometric Resolution

how sensitive is everything to different variations in intensity 

(how much light)

Spherical Aberration

Rays that pass through the edge of the lens don’t focus the same as the rays that pass through the center

Too many focal points, blurry pics

Chromatic Aberration

different colors focus on different spots

can be a result of lens refraction

Astigmatism

lens doesn’t focus light symmetrically the same, resulting in multiple focal points

Defocus

Images from in front or behind the sensor

Coma

incedent light isn’t perpendicular to the optical axis

Field curvature aberration

focal plane is not planar but on a curved image surface

distortion

shifts image position in the local plane

Relief Displacement

A shift in the photographic position of an image caused by the object being above or below the datum

Parallax

the effect whereby the position or direction of an object appears to differ when viewed from different positions

what assumptions do you make when calculating relief displacement

photo is taken vertically, coordinate system is at the principal point, photos are corrected for shrinkage and distorations

Photo Scale

the ration of the photo distance to the ground distance

varies as the height of the ground changes

Average photo scale (S)

ratio of the photo distance to the ground distance

outward facing relief displacement

points above the datum

inward facing relief displacement

points below the datum

dispersion

the variation of the index of refraction as a function of wavelength