Introduction to the Principles of Aerial Photography Some content is from Remote Sensing Core...
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Transcript of Introduction to the Principles of Aerial Photography Some content is from Remote Sensing Core...
Introduction to the Principles Introduction to the Principles of Aerial Photographyof Aerial Photography
Some content is from Remote Sensing Core Curriculum module:
Introduction to Photo Interpretation and Photogrammetry
by John Estes and Jeff Hemphill
Camera componentsCamera components
Similar to an eyeballSimilar to an eyeball Lens focuses light rays onto a Lens focuses light rays onto a
recording mediumrecording medium Recording medium is usually film or a Recording medium is usually film or a
digital imaging sensor (2-D array of digital imaging sensor (2-D array of detectors)detectors)
Focal length is distance between focal Focal length is distance between focal plane (film plane) and center of the plane (film plane) and center of the lenslens
Camera typesCamera types
Many different types of cameras Many different types of cameras developed, especially for military usesdeveloped, especially for military uses
Metric cameras are produced for high Metric cameras are produced for high precision applicationsprecision applications
Large format cameras (> 100mm film size) Large format cameras (> 100mm film size) are common for aerial surveys are common for aerial surveys
Medium format cameras (>35mm – Medium format cameras (>35mm – 100mm) are common for mapping small 100mm) are common for mapping small areas and reconnaissanceareas and reconnaissance
Small and medium format cameras are Small and medium format cameras are common for do it yourself applicationscommon for do it yourself applications
Special considerations for Special considerations for aerial camera systemsaerial camera systems
Hold large amounts of film or storage Hold large amounts of film or storage space for digital camerasspace for digital cameras
Film cameras use vacuum film plates to Film cameras use vacuum film plates to hold film flat against the film platehold film flat against the film plate
Image motion compensation moves Image motion compensation moves camera to compensate for forward aircraft camera to compensate for forward aircraft motionmotion
Stabilized mounts compensate for roll, Stabilized mounts compensate for roll, pitch, and yaw of the aircraftpitch, and yaw of the aircraft
Navigation instrumentation records Navigation instrumentation records position and orientation of aircraftposition and orientation of aircraft
Require aircraft with the appropriate ports Require aircraft with the appropriate ports in the belly of the planein the belly of the plane
RC30 Aerial Camera System
Image from Remote Sensing Core Curriculum Introduction to Photo Interpretation and Photogrammetry by John Estes and Jeff Hemphill
Recording mediaRecording media
FilmFilm Black and whiteBlack and white True colorTrue color Infrared (color and black and white)Infrared (color and black and white)
Sensitivity to different wavelengths varies with Sensitivity to different wavelengths varies with different types of filmdifferent types of film
Digital cameras record images using a 2-Digital cameras record images using a 2-dimensional array of detectorsdimensional array of detectors
Aerial digital cameras are slowly replacing film Aerial digital cameras are slowly replacing film camerascameras
All digital systems improve efficiency of All digital systems improve efficiency of processing since most manual tasks can be processing since most manual tasks can be automatedautomated
PlatformsPlatforms
Aircraft are most commonAircraft are most common Small fixed wing aircraft are relatively Small fixed wing aircraft are relatively
inexpensive but not very stableinexpensive but not very stable High altitude jets are stable but very costly to High altitude jets are stable but very costly to
flyfly Unmanned aerial vehicles (UAVs) are Unmanned aerial vehicles (UAVs) are
growing in popularitygrowing in popularity Remote controlledRemote controlled AutonomousAutonomous
Terrestrial photos acquired from mountains Terrestrial photos acquired from mountains or other features with a high vantage pointor other features with a high vantage point
Terms related to aerial photosTerms related to aerial photos
Fiducial marks: Reference marks on the corners Fiducial marks: Reference marks on the corners and/or sides of aerial photos used to define and/or sides of aerial photos used to define coordinate axes and to locate the geometric coordinate axes and to locate the geometric center of the photocenter of the photo
Principal point: The geometric center of the Principal point: The geometric center of the photophoto
Conjugate principal point: The point Conjugate principal point: The point representing the principal point of an adjacent representing the principal point of an adjacent photophoto
Photo base: The distance between the principal Photo base: The distance between the principal point and the conjugate principal pointpoint and the conjugate principal point
More termsMore terms Nadir: The point on the photo vertically beneath Nadir: The point on the photo vertically beneath
the camera lens at the time of exposurethe camera lens at the time of exposure Isocenter: A point roughly halfway between the Isocenter: A point roughly halfway between the
principal point and nadir from which tilt principal point and nadir from which tilt displacement radiatesdisplacement radiates
Vertical viewing geometryVertical viewing geometry
Tilt less than ~3°Tilt less than ~3° Scale relatively constant if terrain is Scale relatively constant if terrain is
not severenot severe Easier to use for stereo visualizationEasier to use for stereo visualization Direction (angles) can be more Direction (angles) can be more
accurately measuredaccurately measured
Oblique Oblique viewingviewing geometry geometry
Oblique: Tilted off of vertical axis Oblique: Tilted off of vertical axis High oblique: horizon is visibleHigh oblique: horizon is visible Low oblique: horizon not in imageLow oblique: horizon not in image
Covers a larger areaCovers a larger area Sides of objects can be seenSides of objects can be seen Scale decreases toward horizonScale decreases toward horizon Can be difficult comparing to maps or Can be difficult comparing to maps or
orthorectified imagery due to different orthorectified imagery due to different perspectiveperspective
Orthogonal vs. central Orthogonal vs. central projectionprojection
Orthogonal projection Orthogonal projection Each point is placed as if it is viewed from aboveEach point is placed as if it is viewed from above Also called a map planeAlso called a map plane
Central projectionCentral projection Projection of features in an aerial photographProjection of features in an aerial photograph Each point on a photo is imaged after reflected Each point on a photo is imaged after reflected
light passes through a single point (lens)light passes through a single point (lens) Causes features with a height above a base Causes features with a height above a base
elevation to radiate outward from the center elevation to radiate outward from the center
Central projection: aerial photo
Orthogonal projection: map
Image from Remote Sensing Core Curriculum Introduction to Photo Interpretation and Photogrammetry by John Estes and Jeff Hemphill
Image distortion and Image distortion and displacementdisplacement
DistortionsDistortions Film and paper shrinkageFilm and paper shrinkage Atmospheric distortionsAtmospheric distortions Image motionImage motion Lens distortionLens distortion
DisplacementDisplacement Caused by:Caused by:
curvature of the Earthcurvature of the Earth tilttilt topographic relief and height of featurestopographic relief and height of features
Makes stereo viewing possibleMakes stereo viewing possible Allows us to measure heights and make topographic Allows us to measure heights and make topographic
mapsmaps
Shadows: Caused by a feature blocking the Shadows: Caused by a feature blocking the sun’s illumination from another feature or sun’s illumination from another feature or the Earth’s surfacethe Earth’s surface
Hotspot: The area on an aerial photograph Hotspot: The area on an aerial photograph where shadows are hidden by the feature where shadows are hidden by the feature casting the shadow thereby causing a bright casting the shadow thereby causing a bright spotspot
Specular reflection area: An area on an Specular reflection area: An area on an aerial photograph where the sun’s rays are aerial photograph where the sun’s rays are reflected directly into the camera lens reflected directly into the camera lens causing a white spot if a highly reflective causing a white spot if a highly reflective feature is in this areafeature is in this area
Illumination features in aerial Illumination features in aerial photosphotos
Image from Canada Centre for Remote Sensing Glossary of Remote Sensing Terms: http://ccrs.nrcan.gc.ca/glossary/index_e.php?
id=3133
Diagram of specular bright spot and hot spot on an airphotoA = specular reflection bright spot; B = hot spot; C = camera; N = nadir; I = illumination source; theta = angle of incidence = angle of reflection
What is photogrammetryWhat is photogrammetry
The art, science, and technology of The art, science, and technology of obtaining reliable information about obtaining reliable information about physical objects and the physical objects and the environment, through the process of environment, through the process of recording, measuring, and recording, measuring, and interpreting images and patterns of interpreting images and patterns of electromagnetic radiant energy and electromagnetic radiant energy and other phenomena.other phenomena.