CEE 6100 / CSS 6600 Remote Sensing Fundamentals 1 Topic 4: Photogrammetry PHOTOGRAMMETRY DEFINITION (adapted from Manual of Photographic Interpretation, 2nd edition, Warren Philipson, 1997)

Photogrammetry and Remote Sensing: The art, science, and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring, and interpreting imagery and digital representations of energy patterns derived from non-contact sensor systems.

1) metric photogrammetry: making precise measurements from photos. 2) interpretative photogrammetry: recognizing and identifying objects and

judging their significance through careful and systematic analysis. See also: Elements of Photogrammetry with Applications in GIS (2014) Paul R. Wolf, Bon

A. Dewitt and Benjamin E. Wilkinson. McGraw-Hill Education, 4th edition, ISBN: 9780071761123

Photogrammetry: Making precise measurements from images

• Close range photogrammetry: with camera focus set to a finite value. • Far range photogrammetry: with camera focus set to infinity

Basic Optics: thin lens equation: 1𝑜𝑜

+ 1𝑖𝑖

= 1𝑓𝑓

magnification: 𝑀𝑀 = 𝑖𝑖𝑜𝑜

= ℎ′

ℎ= 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑠𝑠𝑖𝑖𝑠𝑠𝑖𝑖

𝑜𝑜𝑜𝑜𝑜𝑜𝑖𝑖𝑜𝑜𝑜𝑜 𝑠𝑠𝑖𝑖𝑠𝑠𝑖𝑖

Long range photogrammetry: focus at infinity thin lens equation:

magnification:

𝑀𝑀 =ℎ′ℎ

=imagesize𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜size

=𝑓𝑓𝑜𝑜

= 𝑆𝑆𝑜𝑜𝑆𝑆𝑆𝑆𝑜𝑜

o i

θ image

f

obje

ct

h

h'

depth of field

i ≈ f o

𝟏𝟏𝒐𝒐

+ 𝟏𝟏𝒊𝒊

= 𝟏𝟏𝒇𝒇

𝒐𝒐 ≫ 𝒊𝒊 𝒊𝒊 → 𝒇𝒇 (𝒐𝒐 → ∞)

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 2 Topic 4: Photogrammetry Horizontal resolution and Scale Resolution will depend on:

• inherent resolution of the film or spacing of detectors in a digital array

• depth of field (circle of confusion)

• characteristics of the optics – lens quality – focal length – imaging geometry

Uniformity of Scale

1. Photo taken with film plane at an angle to the building face. Note that the roof line and

ground line are not parallel. (variable scale)

2. Photo taken with film plane parallel to the building face. Note that the roof line and

ground line are parallel. (uniform scale)

3. Photo of the left end of building taken with film plane parallel to the building face.

Distance from the building is approximately the same as in photo 2.

4. Composite of photos 2 & 3

H = altitude

optic

axi

s

FOV

w

∆d

∆D

f = focal length

𝑆𝑆𝑜𝑜𝑆𝑆𝑆𝑆𝑜𝑜 = 𝑆𝑆 =𝑓𝑓𝐻𝐻

=𝑤𝑤𝐹𝐹𝐹𝐹𝐹𝐹

=∆𝑑𝑑∆𝐷𝐷

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 3 Topic 4: Photogrammetry

Resolution

• The resolution of the system is the measure of how close a pair of lines can be to one another and still be distinguished.

• The smallest separation, d, of a pair of bars that can be distinguished by an imaging system defines its resolution.

The spatial resolution of a digital frame camera will depend on the spacing of the elements in the detector array. The closer the spacing, the higher the resolution will be for a given lens system and focal length. For film the resolution depends on the size of the grains of the silver salts that form the image: the smaller the grain size, the higher the spatial resolution of the film and the slower the film speed. The highest spatial resolutions available for aerial photographic films are typically 200 lp mm-1. This corresponds to a typical grain size of ~1 µm. The detector spacing for a comparable digital frame camera would be ~5-10 µm.

Resolution Test Patterns Sector Star Target (for astigmatism)

.

digital array (or aerial film)

rear nodal point front nodal point

reduced print contact print enlarged print

datum plane

H

f S = f / H

Scale = image distance/ground distance 1:24,000 1" = 2,000 ft. small scale 1:250,000 1 mm = 24,000 mm large scale 1:12,000

Scale

Each test target comes with a chart that specifies the line pairs per mm (l ppm) for each group and element

The aerial version is in line pairs per meter. 30° 22.140'N, 89° 33.959'W

30° 23.161'N, 89° 37.733'W

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 4 Topic 4: Photogrammetry Components of a film mapping camera Lens Assembly: The lenses of aerial systems

are multiple-lens systems with a between-lens field stop and shutter. The focus is fixed at infinity. Typical focal lengths are 3.5, 6, 8.25 and 12 inches.

Focal Plane: This is a plate aligned perpendicular to the optical axis of the lens. A vacuum system is used to fix the film to the plate so the focal plane is perfectly flat during exposure.

Lens Cone: Holds the lens and filter, and covers the front part of the camera preventing light from leaking into the camera body.

Body: Encloses the camera, the mounting bolts and stabilization mechanism. Drive Assembly: The winding mechanism, shutter trigger, the vacuum pressure system and

motion compensation. Magazine: Holds the roll of unexposed film, advances the film between exposures, holds the

film in place and winds-up the exposed film. Magazines may be exchanged in-flight. Focal length: The distance between the rear (emergent) nodal point and the focal plane. Equivalent focal length: The distance along the optical axis to the plane of best average

definition (measured). Calibrated focal length: an adjusted value of the equivalent focal length, computed such that

the effect of lens distortion is distributed over the entire field.

RMK TOP - Aerial Survey Camera System CAMERA TOP

RMK TOP 15 focal length 153 mm (6 "), angular field 93° (diagonal), aperture f/4 to f/22 continuously, distortion <= 3µm RMK TOP 30 focal length 305 mm (12") angular field 56° (diagonal), aperture f/5.6 to f/22 continuously, distortion <= 3µm

SUSPENSION MOUNTT-TL (gyro-stabilization suspension mount)

• Stabilization range: • ± 5° in omega, • ± 5° in phi, • ± 6.5° in kappa

• max. angular speed: 10°/s • max. angular acceleration: 20°/s²

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 5 Topic 4: Photogrammetry Intergraph DMC II250 Specifications • 4 high-resolution 14K x 17K panchromatic cameras

– Final output image: 14,656 x 17,2164 pixels – Field of view: 46.6° cross track x 40.2° along track – Lens system: 4: x f = 120mm/f:4.0

• Four multispectral 7K x 8.5K cameras: red, green, blue, and near infrared – Spectral sensitivity: Blue: 400-580 nm; Green: 500-650 nm; Red: 590-

675 nm; NIR: 675-850 nm; NIR alternate: 740-850 nm. Custom filters available upon request

– Lens system: 4: x f = 25mm/f:4.0 • Shutters and f-stop: continuously variable 1/50 -

1/300 sec, f/4-f/22 • On-board storage capacity: 1.5 TB (1350 images) • Maximum frame rate: 1.7 sec/image • Radiometric resolution: 14 bit (all

cameras) • Ground pixel size: 2.5 cm @ 500 m • Forward Motion Compensation (FMC)

fiducial marks

+x -x

+y

-y

y-fiducial axis

x-fiducial axis

photographic center (principal point)

fiducial ma

Airphoto Hidalgo County, TX http://www.colorado.edu/geography/gcraft/notes/remote/gif/hidalgo.jpg

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 6 Topic 4: Photogrammetry Scale change with topography

Relief displacement

Near-vertical kite aerial photograph. Notice different view of trees near scene center in comparison to trees at far right.

Cucharas Pass, Colorado;

photo date 6/00, © J.S. Aber.

Source: http://academic.emporia.edu/aberjame/airphoto/p_gram/p_gram.htm

•

•

•

DATUM

GROUND

ELEVATION

S = f/(H - h)

Above datum = H Above A: HA' = H - hA Above B: HB' = H - hB f

PHOTO • • b' b

a • • a'

A

B

B'

A'

hA

hB

H

f a

a'

b t

rb' rb

ra' ra

da

RA RB

A

A'

H

hT

hB hA • •

• •

• • • •

datum ground

photo

nadir point

• • b'

rt

dahA

=raH

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 7 Topic 4: Photogrammetry

Source: http://www.photoscience.com/airphoto.htm#Sample Air Photo

Tilted Aerial Photograph

Tilt displacement A point that would have been imaged at a' on a vertical photo is actually imaged at a on the "up side" of the tilted photo. The tilt displacement of points on the "up side" of the tilted photo is then toward the isocenter while points on the "down side" are displaced away from it.

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 8 Topic 4: Photogrammetry • Tilt displacement is

always relative to the isocenter.

• Scale change is in the direction of tilt.

• The nadir point is always on the down side of the axis of tilt and opposite the principal point from the isocenter

The direction of tilt displacement is radial relative to the isocenter. The amount of displacement is proportional to the distance from the isometric parallel.

Oblique photography: Extreme tilt displacement

Image areas on the upper side of the tilt are displaced further away from the ground than is the isocenter and are at smaller scales than the nominal scale. Image areas on the lower side of the tilt are displaced closer to the ground than the isocenter and are at larger scales than the nominal scale. Source: http://www.aboveallphoto.com/oblique_photography.html

perspective center

t

f f

d'

d d''

n'

n

P a a''

a' Equivalent

vertical photo •

•

•

• • • • i

•

A B

•

tilted photo

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 9 Topic 4: Photogrammetry

Relief & Tilt displacement

1. Location of an object on the datum plane for an untilted photo 2. Position of the object on a vertical photo due to relief displacement. (Object is above the

datum plane.) 3. Position of the object on a tilted photo due to tilt displacement.

Stereo Air-photo terminology Principal point: Geometric center of

photograph. Literally the point on the ground in line with axis of camera lens.

Fiducial marks: Marks on the photograph margins used to locate principal point in photo.

Conjugate principal point: Point in overlapping photo that is equivalent to principal point of adjacent photograph.

Photo base: Distance between principal point and conjugate principal point measured on a single photograph.

Ground (air) base: Ground (air) distance between principal points of overlapping photographs. Parallax: Apparent shift in relative positions of objects when viewed (photographed) from

different vantage points.

isometric parallel

principal line

a a''

b b''

p i I

n d d''

e e''

c, c''

• • •

•

•

•

•

• •

• •

•

•

•

•

•

•

•

•

• • •

• •

i p

n

isometric

principal

1 2 3 1

2 3

1 2 3

1 2, 1

2 3

"up side"

"down side"

air base elevation H above datum

1 2

n1'

a b

A

B

a' n1 n2 n2' b'

DATUM

N1

N2

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 10 Topic 4: Photogrammetry Stereo Imagery from a frame camera Determining height from stereo imagery

Determining the height of the Washington Monument using stereo parallax 555 ft 5.9 in (169.314 m)

Stereo Imagery from Mars

http://mars.jpl.nasa.gov/MPF/mpf/stereo-arc.html

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 11 Topic 4: Photogrammetry Height Measurement

O1, O2 = nadir points of photo 1 and photo 2, respectively X1, X2 = location of the base of the tree x'1, x'2 = position of the base of the tree along the flight path dP1, dP2 = relative parallax Change in height

flight path O1 O2 O1 O2

dP1 dP2

x'1 x'2

X1 X2

f

H-h

dp1

o2 o1 x1

h

H

dp2

o2 o1 x2

image plane

rear node (lens)

O1 O2

dP P = absolute parallax

dP1 dP2

parallax difference: dP = dP1 – dP2

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 12 Topic 4: Photogrammetry Flight Planning Factors to consider:

1. General issues • focal length • array/film size (format) • scale / FOV • overlap / sidelap (continuous

coverage, stereo, …)

2. Issues specific to the application • spectral considerations (film / filter) • time of day (illumination, sun orientation,

tidal stage, …) • season (crop calendar, leaf on, leaf off, …) • sun orientation, sun angle

Focal length

• The nominal scale of the photo is the ratio of the focal length to the altitude:

scale = f / altitude • If the image medium can resolve 1 line pair / d, the equivalent ground resolution is:

rgnd = d / scale

• The FOV of the image is related to the film/array format. (e.g., film format: 23 cm (9"); array format: 100 x 57 mm)

𝑭𝑭𝑭𝑭𝑭𝑭 =𝒇𝒇𝒐𝒐𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒇𝒔𝒔𝒔𝒔𝒇𝒇𝒔𝒔𝒔𝒔

• Vertical resolution, a function of the distance between images, the altitude and the film resolution, may be estimated as:

𝒇𝒇𝒉𝒉𝒉𝒉𝒇𝒇 =𝒇𝒇𝒔𝒔𝒇𝒇𝒊𝒊𝒇𝒇𝒂𝒂𝒂𝒂𝒔𝒔 × 𝒇𝒇𝒉𝒉𝒈𝒈𝒂𝒂

𝒂𝒂𝒊𝒊𝒔𝒔𝒇𝒇𝒇𝒇𝒈𝒈𝒔𝒔𝒔𝒔 𝒃𝒃𝒔𝒔𝒇𝒇𝒃𝒃𝒔𝒔𝒔𝒔𝒈𝒈 𝒈𝒈𝒇𝒇𝒂𝒂𝒊𝒊𝒇𝒇 𝒑𝒑𝒐𝒐𝒊𝒊𝒈𝒈𝒇𝒇𝒔𝒔 × 𝒇𝒇𝒉𝒉𝒈𝒈𝒂𝒂

Overlap • Plan for 60% overlap (endlap), especially for stereo flights. • Can be less if stereo is not required

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

coverage of a single photo endlap

nadir line (ground flight path)

horizontal shift and rotation due to drift and correction for crabbing

consecutive frames collected by camera at equal time intervals

photos aligned to fit a base map

photo centers

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 13 Topic 4: Photogrammetry Sidelap

• Plan for 30% overlap (sidelap) in order to insure complete coverage (no gaps).

Sources of Aerial Photography USGS National Aerial Photography Program: https://lta.cr.usgs.gov/NAPP

• Standardized images, cloud-free, every 5-7 years • Collected at 20,000 ft; about 1 m resolution • Centered on one-quarter section of a 7.5-minute USGS quadrangle, and covers

approximately a 5.5 x 5.5 mile area USDA Aerial Photography Field Office https://www.fsa.usda.gov/programs-and-services/aerial-photography/

• Imagery dated beginning with 1955 to the present at this site. • Imagery prior to 1955 are held by the National Archives but must be ordered.

More information here.

National Oceanic and Atmospheric Administration (NOAA) • Coastal Aerial Photography • https://data.noaa.gov/dataset

National Air Photo Library (NAPL) of Canada • http://www.nrcan.gc.ca/earth-sciences/geomatics/satellite-imagery-air-photos/9265

Commercial sources:

• http://www.geomart.com/products/aerial/index.htm • State agencies

flight path

CEE 6100 / CSS 6600 Remote Sensing Fundamentals 14 Topic 4: Photogrammetry Spectral Considerations

What spectral bands will highlight the target in the expected background? vegetation: NIR/Red is characteristic of vegetation mineral exploration: Specific band selection will depend on the minerals in question, but most will be in the Mid-IR or SWIR. water quality: visible channels will dominate.

Seasonal Considerations Will the target be more detectable at some times of year? vegetation: discrimination between oak and maple may be most effective in early spring when maple has leafed out but oak has not. mineral exploration: any season will do if there is no cloud cover (or snow).

water quality: - wet season vs. dry season - temperature regime (thermocline, plankton growth) - seasonal land use changes (tourism, industry, recreation)

Time of day considerations

Will the target be more detectable at certain times of day? vegetation: discrimination between oak and maple may be most effective in early spring when maple has leafed out but oak has not. mineral exploration: shadows may be an advantage (low sun angle) in some cases.

water quality: - tidal stage - relatively high sun angle (to maximize the amount of light entering the water).

Flight alignment

• Flight lines are usually planned to be parallel to each other and parallel to the long axis of the study area. (Minimizes aircraft turns which are very time consuming.)

• Complicating factors: – wind (causes the aircraft to crab or drift across the flight path). – topography (low altitude flights in mountainous areas may result in flight lines

that are not parallel to the long axis of the study area. – restricted zones (airports, military bases), national borders,

• Issues specific to line scanning systems – sun angle effects (BRDF) may be minimized by selecting a flight line into or out

of the sun.