Photogrammetry 1.
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  • 1. What is photogrammetry?
    • Photos – light Gramma – to draw Metron – to measure
      • “ Photogrammetry is the technique of measuring objects from photographs”
    • “ The art, science and technology of obtaining reliable spatial information about physical objects and the environment through the processes of recording, measuring and interpreting image data.”
    • Two distinct types of photogrammetry :
      • Aerial / spaceborne photogrammetry
      • Close range photogrammetry
    • Remember this : Photogrammetry is the metric interpretation of image data
  • 2. Photogrammetry portrayed as systems approach. The input is usually referred to as data acquisition, the “black box" involves photogrammetric procedures and instruments; the output comprises photogrammetric products.
  • 3.  
  • 4. What is photogrammetry?
    • Topographic photogrammetry
    • Used for mapping Earth or planets
    • Imaging system is based on an aircraft or spacecraft
    • Target is the ground surface
    • Image data is processed to create new spatial information products
    • Close range photogrammetry
    • Used for industrial measurement
    • Imaging system is handheld
    • Target is the object being measured
    • Image data is processed to make precise measurements
  • 5. What can photogrammetry do?
    • The simple answer: make accurate 2D and 3D measurements
    • Information required: images and sensor (camera) parameters
    • Close range photogrammetry: 3D only
    • Topographic photogrammetry: 2D and 3D, depending on specific application
    Single photograph + Sensor parameters = 2D measurement Multiple photographs + Sensor parameters = 3D measurement
  • 6. WHY PHOTOGRAMMETRY
    • VERY PRECISE
    • TIME EFFECTIVE
    • COST EFFECTIVE
    • BASED ON WELL ESTABLISHED AND TESTED ALGORITHMS.
    • LESS MANUAL EFFORT
    • MORE GEOGRAPHIC FIDELITY
  • 7. Cont……
    • Corrects all sorts of distortions.
    • provide a reasonable geometric modeling alternative when little is known about the geometric nature of the image data.
    •   provide an integrated solution for multiple images or photographs simultaneously
    • achieve a reasonable accuracy without a great number of GCPs
    • create a three-dimensional stereo model or to extract the elevation information
  • 8.  
  • 9.  
  • 10.  
  • 11.  
  • 12.  
  • 13.  
  • 14. PHOTOGRAMMETRY – Functional Details
  • 15. Types of photographs
  • 16. Image Requirements
    • A block should have at least one pair of images (Satellite or Photo) which overlap:
    Stereo Pair Overlap Region 60% Overlap
  • 17. Overlap Between Runs Not essential but can help 30% overlap between runs or swaths Run #1 Run #2
  • 18. Stereo Vision Left Right Matching correlation windows across scan lines Z ( x , y ) is depth at pixel ( x , y ) d ( x , y ) is disparity baseline depth
  • 19. Cameras and Sensors
      • Pushbroom Sensors - data is collected along a scan line, each scan line has it's own perspective center.
    Perspective Centers
  • 20. Camera and Sensor Types
    • Cameras
      • Frame Camera
      • Digital Camera
      • Video Camera (Videography)
      • Non-Metric Camera (35m, Medium and Large Format Cameras)
    • Pushbroom Sensors
      • Generic
      • Spot
      • IRS-1C
  • 21. Stereo aerial photography
  • 22. Photogrammetry and remote sensing
    • Photogrammetry -> metric exploitation of imagery
    • R emote sensing -> thematic exploitation of imagery
    • SPOT (French RS satellite) broke down the barriers in the 1980’s and 1990’s with:
      • digital linescanner
      • stereo imaging capability
      • high quality optics and orbital model
      •  suitable for regional stereo mapping and remote sensing
    • Ikonos and Quickbird (launched recently) provide high resolution stereo imagery  suitable for large scale mapping and remote sensing
    • Next step: digital aerial frame cameras
  • 23. Digital Cameras   The image plane of a digital camera to be used to record spatial objects contains a two dimensional field of sensors. CCD sensors (Change Coupled Devices) predominate in digital photogrammetric cameras. Such cameras are known as CCD Cameras
  • 24. Satellite topographic mapping
    • Stereo data can be collected on same orbit, or different orbits (beware of changes)
    • Satellite may have to be rotated to point sensor correctly
    • Optimum base to height ratio is 0.6 to 1.0
    • Atmospheric effects (refraction, optical thickness) become more significant at higher look angles
    Different orbits Same orbit
  • 25. Stereo satellite imagery
  • 26. SPOT
    • 1 panchromatic, 3 multispectral channels
    • Panchromatic pixel size of 10m
    • Multispectral pixel size of 20m
    • Good for relief mapping at 1:50000
  • 27. High resolution satellites
    • Ikonos (SpaceImaging)
    • 1m panchromatic and 4m multispectral imagery (NIR, R, G, B)
    • 11 bit dynamic range
    • Camera specifications not available
    • Quickbird (Digital Globe)
    • 0.61m panchromatic and 2.44m multispectral imagery (NIR, R, G, B)
    • 11 bit dynamic range
    • Camera specifications available
  • 28. BRANCHES OF PHOTOGRAMMETRY Analogue Photogrammetry - optical or mechanical instruments were used to reconstruct three-dimensional geometry from two overlapping photographs. The main product during this phase was topographic maps .
  • 29. Analytical Photogrammetry
    • The computer replaces some expensive optical and mechanical components.
    • The resulting devices were analog/digital hybrids.
    • Analytical aerotriangulation, analytical plotters, and orthophoto projectors were the main developments during this phase.
    • Outputs of analytical photogrammetry can be topographic maps, but can also be digital products, such as digital maps and DEMs
  • 30. Digital Photogrammetry
    • Digital photogrammetry is applied to digital images that are stored and processed on a computer.
    • Digital photogrammetry is sometimes called softcopy photogrammetry.
    • The output products are in digital form, such as digital maps, DEMs, and digital orthophotos saved on computer storage media.
  • 31.
      • Single or pairs of digital images are loaded into a computer with image processing capabilities.
      • Images may be from satellite or airborne scanners, CCD cameras or are conventional photographs captured by a line scanner.
      • Images are either displayed on the screen for operator interpretation, enhanced by image processing or subjected to image correlation in order to form a digital elevation model (DEM) or extract details.
    DIGITAL PHOTOGRAMMETRY
  • 32.
      • Creating a 3-D model or map is a straight and linear process that includes several steps-
      • Sensor model defenition
      • Ground Control Point (GCP) measurement
      • Automated tie point collection
      • Block bundle adjustment (i.e. Aerial Triangulation)
      • Automated DEM extraction
      • Ortho-rectification
      • 3-D feature collection and attribution
    DIGITAL PHOTOGRAMMETRIC WORKFLOW
  • 33. Applications of Photogrammetery
    • Topographic mapping
    • Creation of value added products:
      • Orthoimages
      • Digital Elevation Models
      • Virtual landscapes
    • Nadir imagery is essential for mapping
    • Overlap and sidelap is required to give 3D information
  • 34. Example products: maps
  • 35. Example products: DTMs
  • 36. Example products: Virtual landscapes
  • 37.  
  • 38. DTMs
    • Sources of terrain models
      • Stereo photogrammetry
      • Interferometric radar
      • Stereo radar
      • Laser scanning
      • Digitising maps
  • 39. Contour digitizing
    • Digital terrain model – Digitizing contour maps
    • Two step procedure: click on the contours, then grid the data
    • Liable to error if the DEM spacing grid is too large
  • 40. Contour digitizing
  • 41. Contour map
  • 42. Radar mapping from space
    • Two methods of topographic mapping using synthetic aperture radar (SAR):
      • Stereo imaging ( radargrammetry )
      • Radar interferometry
    • Advantages of Radargrammetry:
      • 24 hour imaging
      • Physics of the imaging process is well understood
      • Radar relief mapping at 1:50000 is possible
    • Disadvantages of Radargrammetry :
      • Radar images have significant geometric distortions
      • Shadow and layover caused by relief
      • Radiometric interpretation is difficult
  • 43. Radar mapping from space
  • 44. Stereo radar imagery
  • 45. DEM
  • 46. Stereo photogrammetry
  • 47. Airborne laser scanning
    • Digital terrain model generation – airborne laser scanning
    • Laser pulse is emitted from the sensor – return journey time is measured, giving distance between sensor and target
    • Location of the sensor is determined by GPS
    • Therefore target can be located
    • Significant post processing is required:
      • Data thinning
      • Gridding
  • 48. LIDAR data Horizontal resolution: 2m Vertical accuracy: ± 2cm
  • 49.  
  • 50. Modelling building and topological structures
    • Two main approaches:
      • Digital Elevation Models (DEMs) based on data sampled on a regular grid (lattice)
      • Triangular Irregular Networks (TINs) based on irregular sampled data and Delaunay triangulation
  • 51. DEMs and TINs DEM with sample points TIN based on same sample points
  • 52. Advantages/disadvantages
    • DEMs:
      • accept data direct from digital altitude matrices
      • must be resampled if irregular data used
      • may miss complex topographic features
      • may include redundant data in low relief areas
      • less complex and CPU intensive
    • TINs:
      • accept randomly sampled data without resampling
      • accept linear features such as contours and breaklines (ridges and troughs)
      • accept point features (spot heights and peaks)
      • vary density of sample points according to terrain complexity
  • 53. DEM Hill shaded DEM Aspect Shaded Aspect Slope Slope draped on DEM DEM derived Variables
  • 54. height slope aspect hillshading plan curvature Feature extraction DEM derived Variables
  • 55. Hydrologic Modeling
    • DEMs allows automated modeling of hydrology
    • Hydrologic modeling is a process that begins with a DEM
    • Types of models: flow direction, flow accumulation, watershed delineation, and flow length
  • 56. Flow Direction
    • Calculates flow direction for every cell in the GRID
    • Based on direction of steepest slope in local neighborhood
    1 2 4 8 16 32 64 128
  • 57. Flow Accumulation
    • Based on flow direction grid
    • Creates a grid of accumulated flow to each cell
    • Can be used to create a stream network
  • 58. Flow Accumulation -> Streams
    • Use a conditional statement to create a stream network from a flow accumulation grid
    • streams =con (flow > 100, 1)
  • 59. Delineating Watersheds
    • Determines the contributing area above a set of cells in a grid
    • Needs a flow direction grid and sources
  • 60. Flowlength
    • Calculates distance along a flow path for each cell
    • Goes either upstream (to the nearest ridge) or downstream (to the nearest sink or outlet)
    • Primary use is to determine the length of the longest flow path in a basin
  • 61. Visibility Analysis
    • Requires:
      • DEM
      • Viewpoint/s
    • What it tells you:
      • Line of sight
      • Viewshed
      • Combined Viewshed
      • Cumulative Viewshed
    Viewing point
  • 62. Calculating an inter-visibility matrix Offset b Offset a v v v nv nv nv visible not visible without offset b with offset b
  • 63.