TO Ka Yi, Lizzy 6 May

Transcription

1 TO Ka Yi, Lizzy 6 May

2 Contents Basic concepts Practical Issues Examples 2

3 Data Acquisition Source of Energy Data Products Interpretation & Analysis Digital Propagation through the atmosphere Data Processing Pictorial Data Analysis Re-transmission through the atmosphere Users Digital Information Products Visual GIS Analysis Internet or Intranet Information Dissemination 3

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5 Data Acquisition Source of Energy Sensor Platform Propagation through the atmosphere Imaging Sensor Re-transmission through the atmosphere 5

6 Characteristics of Sensor Platform Flying height Speed (overlapping/image motion/productivity) Payload (type and weight) Mobility (site constraints/weather conditions/relevant legislation) Temporal resolution Navigation system GNSS and IMU Power supply Weight Etc. 6

7 Examples of Sensor Platform Satellite Fixed-wing aircraft Helicopter UAV Car-based MMV Backpack MMS 7

8 Sensor Platform Specifications Example Operating Height Speed Satellite Landsat km 27,360 km/h Fixed-wing aircraft Jetstream ft 160 kt (300 km/h) Payload Type Optical sensor LFDAC, DC, LiDAR Revisit cycle 16 days Dep. on weather & air traffic Helicopter EC 155 B ft kt ( km/h) LiDAR, DC Dep. on weather & air traffic UAV Car-based MMV (along roads) Backpack MMS (hiking trails, village areas) DJI Phantom ft 54 km/h DC Dep. on weather & power supply Survey Van Ground level km/h DC and LS Human Ground level 5 km/h DC Dep. on weather & road traffic Dep. on weather & pedestrian flow 8

9 Characteristics of Imaging Sensor Active / passive sensor Metric / non-metric sensor Film / digital and image / laser / radar sensor Spectral resolution (channels and bandwidth) Radiometric resolution (256 for 8-bit) Spatial resolution (pixel size / resolving power / scanning resolution) Measuring range and accuracy Focal length and FOV (wide-angle / normal angle) Frame size / Coverage / Swath width 9

10 Examples of Active Sensor Canadian RADARSAT-2 LiDAR Survey Handheld laser scanner 10

11 Examples of Passive Sensor Digital aerial camera Space-borne optical sensor Analogue aerial camera Multi-head oblique cameras Thermal sensor Handheld camera 360 degree panoramic camera 11

12 Characteristics of Imaging Sensor Sensor UAV RMK-TOP UltraCam Eagle LiDAR WorldView-3 Gaofeng-2 Spot 6/7 Resources Satellite 3 Landsat 7/8 Ground Sampling Distance (GSD) 2 cm at 300 ft with 20 mm lens 7.5 cm at 6,000 ft with 300mm lens 4.5 cm at 6,000 ft with 210mm lens 10 cm (H) and 7 cm (V) at 4,000 ft 0.31 m PAN and 1.24 m MS 0.8 m PAN and 3.2 m MS 1.5 m PAN and 6 m MS 5.8 m MS 15 m PAN and 30 m MS 12

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14 Data Acquisition Source of Energy Propagation through the atmosphere Re-transmission through the atmosphere Data Processing Geometric characteristics of aerial photos Pre-processing Geo-referencing Accuracy assessment 14

15 Geometric characteristics of aerial photo Obtain linear/height/angular/positional measurements of ground features from aerial photos Geometric characteristics Perspective Projection Photo-scale Relief Displacement GSD and Spatial Resolution Stereopair Photo 15

16 Perspective projection Camera/exposure station Focal length Image coordinate system Principal point 16

17 Perspective projection Central perspective Elevated points are distorted away from the centre 17

18 Photo Scale (S) S = f/h f focal length H height above terrain 18

19 Relief Displacement (d) Possible used as a map??? Same Scale on flat terrain? Same Scale on hilly terrain? differences in size, shape and location Facilitate stereoscopic viewing and height measurements 19

20 Photogrammetric measurements (single photo, flat terrain) Planimetric (AB) AB/H = ab/f Height (H ) H = (f/ab)*ab H flying height above terrain f focal length ab photo measurements AB = object size 20

21 Photogrammetric measurements (single photo, various terrain height) d / r = h / H d - Relief displacement r radial distance h height of object above datum H flying height above datum 21

22 Ground Sampling Distance The corresponding size on ground of a pixel of a given image sensor at a specified focal length and flying height Calculated GSD = pixel size * photo scale (flying height /focal length) Focal Length Image Altitude Scanning Resolution Film Imaging O O O Digital Imaging O O X 22

23 Ground Sampling Distance Example : flying height at 6000 ft, focal length = 305 mm, Please calculate the Photo Scale. Example : scanned pixel size = 12.5 µm, Please calculate the GSD. 23

24 Y-Parallax Incorrect orientation of the photographs Scale (height) difference between photographs Tilted photographs 24

25 Y-Parallax Setting up Stereo Pairs Correctly (remove Y-parallax) Photographs must be lined up so that both pairs of Principal Points follow the flight line Reconstructed the flight line must lie along the axis of the stereoscope 25

26 X-Parallax Parallax is the apparent displacement in the position of an object, with respect to a frame of reference, caused by a shift in the position of observation Parallax of any point is directly related to the elevation of the point (parallax increase for higher points) A properly oriented stereopair Enable stereoviewing Enable measuring the planimetric position and height of a point For higher points, parallax smaller or larger? 26

27 Parallax equation Parallax equation X a = B * x a / P a Y a = B * y a / P a h a = H (B*f)/P a h a the elevation of point A above datum X a and Y a ground coordinates of point A H flying height above datum B air base f focal length P a x-parallax of point A 27

28 Collinearity Transformation of coordinates from image space to ground space or vice versa By space resection and space intersection Accuracy depends upon the angles of intersection Apply computer processing and least square bundle adjustment X 1, Y 1, Z 1, ω 1 - ϕ 1 -κ 1 X 2, Y 2, Z 2, ω 2 - ϕ 2 -κ 2 28

29 Collinearity Equation Applicable to vertical photos, tilted photos, terrestrial photo, non-metric camera (UAV), satellite imagery, 360 degree panorama photos, aerial triangulation, multi-ray processing, GNSS/IMU geo-referencing x a = -f * [m 11 (X a -X L ) + m 12 (Y a -Y L ) + m 13 (Z a -Z L )] [m 31 (X a -X L ) + m 32 (Y a -Y L ) + m 33 (Z a -Z L )] y a = -f * [m 21 (X a -X L ) + m 22 (Y a -Y L ) + m 23 (Z a -Z L )] [m 31 (X a -X L ) + m 32 (Y a -Y L ) + m 33 (Z a -Z L )] Where x a and y a are the image coordinates of point a f is the focal length M s are functions of the rotation angles omega, phi and kappa X L Y L Z L are the ground coordinates of camera station Xa Ya Za are the ground coordinates of point a 29

30 Collinearity Equation Space Resection Find all six elements of exterior orientation (of a single photo) X L, Y L and Z L and (ω- ϕ-κ) Minimum 3 full GCPs (X, Y, Z) 6 equations for 6 unknowns 30

31 Space Intersection by Collinearity Known (X L1, Y L1, Z L1, ω 1, ϕ 1,κ 1 ) and (X L2, Y L2, Z L2, ω 2, ϕ 2,κ 2 ) Determine X, Y, and Z ground coordinates of new points 4 equations for 3 unknowns 31

32 Data Processing Workflow Analog Workflow Analog Acquisition Transfer Film Development Scanning Georeferencing and AT Application, e.g. Stereo, Mapping, Ortho Analog -> Digital Digital Workflow Digital Acquisition Download Image Preprocessing Georeferencing and AT Application, e.g. Stereo, Mapping, Ortho Full Digital Workflow 32

33 Image Pre-processing for Satellite Imagery Image Pre-processing for Satellite Imagery Level 0 (raw) Level 1A/1B (radiometric & geometric correction) Level 3A/3B Level 2A/2B (map projection/georeferenced) (Orthorectified/ Mosaicked) Atmospheric correction (scattering/absorp tion/haze removal) Application, e.g. NDVI, Ortho Level X Products 33

34 Geo-referencing Method The process of determining X, Y and Z ground coordinates of individual points Aerial triangulation with GCPs and/or GNSS/IMU Direct geo-referencing with GNSS/IMU data only 34

35 Aerial Triangulation Based on measurements from a block of photos Use of collinearity equations Least square bundle adjustment support post-adjustment statistical analysis for error detection and indication of accuracy support photos of any focal length, tilt, and flying height determine camera calibration data support GNSS/IMU data 35

36 Direct georeferencing GNSS/IMU device to obtain EO parameters No GCPs needed for lower order accuracy 36

37 Accuracy assessment of aerial photo Error sources (mostly corrected in georeferencing processes IO & AO) Relief displacement (Observables ) Tilt (corrected in AO) Image distortion (film/scanning processes) (corrected in IO) Differential shrinkage (corrected in IO, negligible in digital image) Lens distortion (corrected in IO) Focal plane flatness (corrected in IO, negligible in digital image) Atmospheric distortion (corrected in IO) Earth curvature distortion (for high flying height > 20,000 ft (corrected in IO) Unequal flying height (corrected in AO) Transferring principal points (corrected in AO) Image measuring error * 2 37

38 Accuracy assessment of aerial photo Simplified photogrammetric equations for stereoscopic measurements Planimetric X = H /f (ab) Height dh = dp * (H /f) * (H /B) H the flying height above terrains f focal length ab photo measurements dp difference in parallax between 2 points B air base 38

39 Accuracy assessment of aerial photo Planimetric σ X = σ m * (H/f) Height σ h = σ p (H/f) * (H/B) σ h = 1.4σ m * (H/f) * (H/B) σ p measuring accuracy of parallax σ m measuring accuracy of image coordinates (affected by spatial resolution) 39

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41 Data Acquisition Data Products Source of Energy Propagation through the atmosphere Data Processing Pictorial Re-transmission through the atmosphere Digital Photogrammetric plot Orthophoto 41

42 Data Products Derived data products Photogrammetric Plots Orthophoto (classic/true) 360 degree panoramic images Geo-referenced video Digital Elevation Model (DEM) 3D model Interferogram Post-processed thermal / multi-spectral / hyper-spectral images 42

43 Photogrammetric plots (photos) 3D digitization and photo interpretation on stereomodel Feature extraction according to mapping project specifications Vector format Incompletion due to obscured area Need field completion and verification for quality checking 43

44 Photogrammetric plots (photos) Stereoscopic measurement of parallax makes use of the principle of the floating mark 44

45 Photogrammetric plots (photos) 45

46 Orthophoto Geometrically rectified aerial photo Advantages Show pictorial information of infinite number of ground objects Geo-referencing product with uniform scale support taking measurements Seamless Support GIS analysis Limitations Existence of shadow areas Lack of height information and annotation (Photo borrowed from SMO website) Time consuming in producing true orthophoto 46

47 Production of Digital Orthophoto Aerial photography Scanning (for film only) Geo-referencing Seamline editing Orthophoto generation DTM digitization Colour Balancing Mosaicking QA/QC Final Orthophoto 47

48 DEM Generation DEM is generated to remove relief error

49 Building lean on Orthophoto

50 Quality indicators Planimetric positional accuracy Geo-referencing DTM editing Seamline editing and mosaicking Logical geometry Illogical building leaning direction Discontinued features Radiometric quality colour balancing and enhancement 50

51 Seamline 51

52 Seamline Editing 52

53 Inconsistent colour matching 53

54 True Orthophoto Buildings show a leaning appearance existence relief displacement distortion Buildings shown in correct planimetric position - relief displacement corrected 54

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56 Data Acquisition Source of Energy Data Products Interpretation & Analysis Digital Propagation through the atmosphere Data Processing Pictorial Data Analysis Retransmission through the atmosphere Users Digital Visual Information Products GIS Analysis Internet or Intranet Information Dissemination 56

57 Data Analysis and Application Mapping Photo records to comply with statutory requirements Freezing survey Land control and lease enforcement Aerial Photo Interpretation Photo evidences in adverse possession case NDVI Study for tree survey Heritage preservation Heat island study 57

58 Data Analysis and Application Compare the land record with ground features Land record Orthophoto (year 1963) Orthophoto (year 2015) 58

59 Data Analysis and Application Compare the coordinates, heights and dimensions Aerial photo in year 1963 Aerial photo in year

60 Data Analysis and Application Time 1 Structure at the left Area:102sm Height:+ 3.5m Structure at the right Area:106sm Height:+ 3.0m Time 2 60

61 Data Analysis and Application 61

62 Data Analysis and Application Aerial Photo Interpretation To facilitate the identification of feature on stereo viewing model formed by aerial photographs To allow dimensioning on the viewing model To detect changes Size, shape, pattern, tone, texture, shadows, location, association, resolution, image scale, image quality 62

63 Data Analysis and Application Black and white Colour Near infra-red 63

64 Data Analysis and Application Image Bit Depth Number of Band 16-bit RGBI bit RGB bit CIR

65 Data Analysis and Application 1:250,000 / 1:500,000 Landsat-8 6 images GSD 15 m PRDM250S PRDM500S 65

66 Data Analysis and Application SPOT-5 satellite image 66

67 Data Analysis and Application

68 Data Analysis and Application

69 Data Analysis and Application

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71 References J.C. McGlone, (2004). Manual of Photogrammetry. USA: ASPRS S.Morain & S.L.Baros, (1996). Raster Imagery in Geographic Information Systems. USA: OnWord Press P.R.Wolf & B.A.Dewitt, (2000).Elements of Photogrammetry. USA: McGraw- Hill J.Shan & C.K.Toth, (2009). Topographic Laser Ranging and Scanning. USA: CRC Press T.M.Lillesand & R.W.Kiefer, (1994). Remote Sensing and Image Interpretation. USA: John Wiley & Sons K.H.Y.Ho & M.I.Wallace, (2006). A basis Guide to Air Photo Interpretation in Hong Kong: Ove Arup & Partners Hong Kong Ltd. R.Graham, (1998). Digital Imaging. UK: Whittles Publishing Positional Accuracy Handbook, Minnesota Planning Land Management Information Centre, October 1999

72 References Airliner.net - http// Baidu - Business Insider - Car Show Room - DigitalGlobe - DJI - MapMart - Microsoft UltraCam Blog - PointGrey - Satellite Imaging Cooperation 2/ SASMAC - SMO - Space Flight USGS

73 THANK YOU 73