Introduction to Photogrammetry
Dr. Moonis Zaheer
Definitions
• Remote Photogrammetry: ”The science or art of obtaining reliable measurements by means of photographs.”
• ”Photogrammetry is the art, science, and technology of obtaining reliable information about physical objects and the environment through the processes of recording, measuring, and interpreting
photographic images and patterns of electromagnetic radiant energy and other phenomena.”
• Analog Photogrammetry: Using optical, mechanical and electronical components, and where the images are hardcopies. Re-creates a 3D model for measurements in 3D space.
• Analytical Photogrammetry: Analytical Photogrammetry The 3D modelling is mathematical (not re-created) and measurements are made in the 2D images.
• Digital Photogrammetry: Digital Photogrammetry Analytical solutions applied in digital images. Can also incorporate computer vision and digital image processing techniques.
• Softcopy Photogrammetry: ”Softcopy” refers to the display of a digital image, as opposed to a ”hardcopy” (a physical, tangible photo).
Definitions
Photograph vs. Image
Photograph
• A scene which was detected as well as recorded on film.
• Chemical reactions on a light sensitive film detects the
intensity of the incoming energy.
• Simple, cheap, well known.
• Only sense in the wavelength of 0.3 – 0.9 µm, manual
interpretation.
Image
• A scene which was detected electronically.
• Generate an electrical signal proportional to the incoming energy.
• Can sense in many wavelengths, data can be easily converted into digital form for automated
processing.
• Complex, Expensive sensors
Relationships of the Mapping Sciences as they relate to
Mathematics and Logic, and the Physical, Biological, and Social
Sciences
History of Aerial Photography
• Origin of Remote Sensing
• Remote sensing began with aerial photography
• First photographs taken in 1839
History
History
• Extracting geometrical
information and producing maps.
• Cheaper than terrestrial methods.
• Extracting qualitative information.
• High speed of map generation.
Why Photogrammetry
• Ideal technology when measuring objects such as
Vast regions to be mapped
Irregular shapes and
Objects that are too
• Hot or cold
• Soft
• Delicate
• Inaccessible
• Toxic
• Radioactive to touch
Why Photogrammetry
Photogrammetric products
• Planimetric maps:
• Planimetric elements in geography are those features that are independent of elevation, such as roads, building footprints, and rivers and lakes. They are represented on two-dimensional maps as they are seen from the air, or in aerial photography. These features are often digitized from
orthorectified aerial photography into data layers that can be used in analysis and cartographic outputs.
• Topographic maps:
• A type of map characterized by large-scale detail and quantitative
representation of relief, using contour lines. Traditional definitions require a topographic map to show both natural and man-made features. A
topographic map is typically published as a map series.
Photogrammetric products
3D points
• LiDAR has become the technology of choice for deriving highly accurate terrain data and 3D models, and it is commonly used for a variety of mapping applications.
General Flow
Production line mapping using Aerial Photogrammetry
Photogrammetric Types
• Photogrammetric Types from Applications Point of View (d is distance from camera to object)
• Close Range Photogrammetry d<10 m
• Terrestrial Photogrammetry 10 m<d<100 m
• Aerial Photogrammetry 2 km<d<10 km
• Space Photogrammetry 30 km<d
Close Range Photogrammetry Terrestrial Photogrammetry
Aerial Photogrammetry
Space Photogrammetry
Types of photographs (categorized by tilt)
• Vertical - camera axis as nearly vertical as Possible
• Oblique - camera axis intentionally tilted
Low Oblique
High Oblique
Vertical Aerial Photogrammetry
Low Oblique
High Oblique
Vertical aerial images are not map!
• Maps are based on parallel projection while photo has central projection
• Maps have a unique scale while image scale varies depending on terrain relief
• Maps are interpreted while photos should be interpreted
• Photo is detailed while maps are generalized
Projection Systems
Taking Vertical Aerial Photographs
Forward Overlap (End Lap)
Aerial Photography – Stereo pair
Over lap Side Overlap (Side Lap)
Taking Vertical Aerial Photographs
• Position of camera at each exposure called exposure station
• Flying height - altitude of camera
• Adjacent flight strips overlap - side overlap
• Block of photos - photos of 2 or more side lapping strips
