1. Digital Photogrammetry by G.C.Nayak 01-06-2010

2. Point of Discussion Approch to Photogrammetry: Integrated with RS Process Involved Issues Involved in each Process

3. What do we mean by; Photogrammetry: Photo (light) + gram (write) + metron (measurement) defined as the art, science and technology of obtaining reliable information about physical objects and environment through the process of interpreting, measuring and recording From photographs

4. Remote Sensing: Remote (distance) + Sensing (gathering information / making inference) Defined as the Science &Technology of making inference about material / objects from measurements made at a distance without coming into physical contact with the objects under study.

5. Examples: - How we see by our Eye - Photographs Taken from Ground (Terrestrial) or Above (Aerial) - Satellite Image taken from space

6. In General we mean by; Photogrammetry- concern with Aerial Photos Remote Sensing- concern with Satellite imageries But both are the Products of Remote Sensing Therefore Photogrammetry as we mean can be dealt as a part of Remote Sensing Only Classes are different

7. Let us go back to the Definition of RS What is being Sensed in RS ? Reflected & Emitted Light energy from the Object of interest is sensed and recorded by our Eye, Camera or Satellite Sensors

8. In the Sensing Process Elements Involves are: The energy – EMR Sensor – The equipment which sense Platform – Where the sensor is placed Depending on the above elements Aerial Photographs & Satellite image are Products of two different class

9. How these can be classified? i.Depending on the EMR used: Which part of the EMS is sensed, Example: Visible, IR, Thermal, Microwave, Xray etc.

10. Measuring Light: Bands Human eyes only ‘measure’ visible light Sensors can measure other portions of EMS Bands

11. Depending on the Sensor used: i.Active Sensor i.Passive Sensor

12. Depending on Plat form: i.Terrestrial: ii. Air borne: iii. Space borne: If Space born Geostationary Sunsynchronous

13. The process of remote sensing A. Radiation and the atmosphere B. Interaction with target C. Energy recorded and converted by sensor D. Reception and processing E. Interpretation and analysis A A B D E C 12 65 28 33 76

14. For mapping purpose we use ; Aerial photographs having overlaps obtained from Airborne camera which sense visible & a part of NIR of EMR Product format: - Analogue / Hard copy from frame camera - Digital image from Digital camera

15. Satellite image from Space borne sun synchronous satellite which sense visible and IR part of EMR Product format: Digital image in bands

16. Aerial photo vs. Satellite image for spatial data extraction Because of low flying ht. Aerial photo capable of providing: - High spatial resolution image/ photographs - Stereo viewing capability for precise ht. measurements

17. With the development in space technology satellite is also capable of providing : - High spatial resolution image -Stereo viewing capability, though not yet attend the precise level that of aerial photo

18. Technology involved in data extraction: i.Photogrammetry By using the geometry of a pair of overlapping stereo image for measurements in 3D ii. Image Processing By processing a single digital image for interpretation and data extraction

19. Aspects involved in data extraction: i.Quantitative – measurement of coordinates (XYZ), length, area, shape Photogrammetric solution precisely does this ii. Qualitative – This is about interpretation, recognition, identification Spatial resolution and contrast of the image influence the both aspects

20. By photogrammetry method: Requirements: - Overlapping image for stereo view required for 3d viewing & measurement - Ground Control Points( XYZ) for establishing positional relationship between photo & ground

21. How Stereo Overlap Aerial image obtained? Stereo Pair Overlap Region 60% Overlap By having an overlap in successive photos Forward Overlap

22. Before information is extracted The conditions as it was during are the photography is recreated A relationship is established the photo / image and the ground system The whole process to find the solution is called Orientation Then data are collected in 3d or 2d environment

23. Evolution of Photogrammetric technique

24. Evolution of Photogrammetric technique ; Phase →Phase –I Analogue Phase –II Analytical Phase –III Digital InputAnalogue / Hard copy Analogue / Hard copy Digital SolutionAnalogue Mech./Opt. Math. Data Acqusition Manual Manual / Automatic Out putAnalogueAnalogue / Digital Digital

25. Digital Photogrammetry is also called Soft copy Photogrammetry Mathematics is the same as in traditional Photogrammetric technology. The images (diapositives) are replaced by scanned aerial images / image acquired in digital form. Measurements and image viewing are on a computer screen instead of through high quality optics.

26. In Digital photogrammetry input is Digital Image obtained through scanning hard copy photo or direct from Digital camera

27. The main work flow involed; Input ( digital image) – output of digital camera or through scanning of photographs Solution – Through process called Aerial Triangulation Generation of DEM – for surface Generation of Orthophoto – Equivalent of Maps for 2D digitisation 3d Data capture Prducts – Input for GIS, Cartographic products (Maps)

28. MAIN WORK FLOW INPUT Photo Coordinates PROCESSING Triangulation OUT PUT EO Parameters – Establishment of relationship between Image and Ground PRODUCTS DEM& Contour, Ortho Photo, Feature Extractions

29. Establishment of Relationship

30. Established through Six Elements of Exterior Orientation X Axis Y Axis Z Axis X,Y, Z,,,, ,, X Z,,,, ,, These 6 parameters define location and orientation of each exposure station/ perspective center

31. DURING TRIANGULATION THE FOLLOWING UNKNOWNS ARE SOLVED AS UNDER:- - EXTERIOR ORIENTATION (EO) PARAMETERS (X 0,Y 0,Z 0,  ) - COORDINATES OF IMAGE POINTS IN GROUND TERMS EO PARAMETERS -X0,Y0,Z0- ARE THE COORDINATES OF THE EXPOSURE STATIONS IN GROUND TERMS - , ,  ARE THE ORIENTATIONAL PARAMETERS OF THE CAMERA

32. Once that solution is found; Further products are obtained by extracting the information Products: 2D / 3D Features, DEM, Ortho images

33. Issues to be addressed during Process; Project Parameters Scanning AT DEM Generation Ortho image Generation 2D / 3D data Capturing

34. Project Parameters; Camera / Sensor Model Frame / Digital / Sensors Coordinate System Horizontal and Vertical Datum / Projection System

35. Scanning What should be the Scanning Resolution? We can not achieved better then the Resolving Power of the used frame camera expressed in line pair / mm (lpm). Ideal case it is 50 lpm equivalent to 10 micron Practically achievable as best 40 lpm equivalent to 12.5 micron Or 25 lpm equivalent to 20 micron

36. Aerial Triangulation (AT) -Number & pattern of GCP AS principle remain same, only technology has changed. Thus the established pattern of GCP in Analogue & Analytical method holds good - Coordinate System -Number of Iteration -Convergence -Statistical Weights Image Points, GCPs, etc.

37. AT Continued….. -Accepted norm of accuracy in X,Y,Z Required accuracy level depending on the output scale and purpose +/- 1pixel in x,y and =/-1.5 pixel term in z is achivable

38. Tie Point Measurements For a solution of number photographs only GCPs are not sufficient Thus Tie points are measured in all overlapping images Issues Automatic or Manual Number and Distribution per images If automatic what are the parameters

39. Parameters for Auto Tie Point This employs Image matching technique Correlation size Search window size Correlation Tolerance

40. DEM GENERATION & ORTHO RECTIFICATION - Once the Triangulation is over, xyz coordinates of any point can be extracted. - During DEM generation - Mass points are generated through out the overlapping area. - Taking mass points TIN is generated - Grid is generated with the defined grid size. Out put is an image file where pixel value is the height. Generation of contour: - From DEM contours are generated. USING DEM DISTORTIONS DUE TO RELIEF & TILT ARE RECTIFIED – OUT PUT IS ORTHOPHOTO ie. Transforming from A perspective projection to orthogonal projection

41. What is Digital Elevation Model (DEM) ? A surface generated from sample points having x,y,z

42. What is orthophoto? Bringing from central Proj. to Ortho. Proj. Error due to relief is corrected using DEM Process called ortorectification

43. Issues to be addressed for DEM generation: -Purpose of DEM For Orthophoto or Contour generation or any other surface analysis The purpose will influence the mass point / break line collection for DEM generation -Resolution of Grid ( Raster DEM) How data will be used / integrated will influence the grid size Generally it is 2-3 time denser than observed density Working procedure is TIN to Grid

44. Issues to be addressed for Ortho Image generation: Error will be more as we move away from the nadir Resolution Depends on Scan Resolution It should be resample to 1.2 time or more Output scale DEM Resolution

45. Feature Extraction: Planimetric : In 2D environment; -From Orthophoto using feature code Feature vertex comprises of only x,y DEM contains surface height information which is used in GIS for analysis If required Contour is generated from it

46. In 3D environment; - Features are digitised in stereo viewing with feature codes - Stereo viewing by alternative or Simultaneous display - Feature vertex comprise of x, y & z - Features such as stream, ridges etc are introduced as break lines for generating DEM - For DEM mass points are collected with operator intervention

47. Issues to be addressed while collecting features: -2D or 3D Purpose Specific -Scale of out put -Zoom level of viewing -Features to be collected - Geometry of a feature (Point, line or Polygon) -Feature class

48. Digitisation Mode; -All Features, Natural & Cultural (Man made),are Digitised / traced manually -Height features through DEM is Automatic -Interpretation and entering of vertex is subjective on the part of Operator

49. Out turn of Feature collection; - As Features are collected (traced) Manually The out turn is almost same as in Analogue - Irrespective of Scale and type of terrain the number Data points entered by the operator remain same So optimum zoom level and density of points as per requirement should be maintained Various experience indicate 3000 -4000 data points per man days in 3D data captures and In 2D it is 2 – 2.5 times

50. Scope of Automation; -It is complex issue to adopt an algorithm to interpret the image while recognizing features as human mind in coordination with eye does -Development is in the process in computer vision involving Artificial Intelligence (AI) using Image geometry, position and dimension Example ; Automatic Building Extraction

52. Approach for purchasing Software Modular Approach for required Functionality Image/Frame Manager Module Ground Control/Tie Point Measurement Module Aerial Triangulation Module DEM/DTM Generation Module Orthophoto Generation Module Stereo Editing Module: Minimum hardware specifications

54. Any questions?