CEE 6100 / CSS 6600 Remote Sensing Fundamentals 1 Topic 4: Photogrammetry PHOTOGRAMMETRY DEFINITION (adapted from Manual of Photographic Interpretation, 2 nd 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: 1 + 1 = 1 magnification: = = ℎ ′ ℎ = Long range photogrammetry: focus at infinity thin lens equation: magnification: = ℎ′ ℎ = imagesize size = = o i θ image f object h h' depth of field i ≈ f o + = ≫ → (→∞)
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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:
• 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
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
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.
• 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
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)
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
• 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
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