1 Koert Sijmons Introduction on Photogrammetry By: Koert Sijmons

2 Koert Sijmons How to create a DEM from a Stereo Photo-pair ?

3 Koert Sijmons Topographic map Aerial photograph

4 Koert Sijmons Difference between map and photo MAP PHOTOGRAPH Orthogonal projection. Central perspective projection Uniform scale. Variable scales. Terrain relief without distortion (contour lines). Relief displacement in the image All objects are represented also the non visible Only objects that are visible. An abstract representation Is a real representation of the earth surface, no legend needed. Cont.

5 Koert Sijmons Difference between map and photo Cont. Representation geometrically correct Representation geometrically not correct Elements appear displaced in its real position and in different shapes, due to the generalization process. Objects appear displaced due to geometric distortions. MAP PHOTOGRAPH

6 Koert Sijmons Basic principles of Photogrammetry Photogrammetry is the science and technology of obtaining spatial measurements and other geometrically reliable derived products from photographs. Obtaining approximate distances, areas, and elevations using hardcopy photographic products with unsophisticated equipment Photogrammetric analysis procedures can range from: Geometric concepts to generating precise digital elevation Models (DEMs), Orthophotos,and thematic GIS data Cont.

7 Koert Sijmons Introduction The terms digital and softcopy photogrammetry are inter- changeable to refer to any photogrammetric operation involving the use of digital raster photographic image data rather than hardcopy images. Digital photogrammetry is changing rapidly and forms the basis for most current photogrammetric operations. However, the same basic geometry principles apply to traditional hardcopy (analog) and softcopy (digital ) procedures. Cont.

8 Koert Sijmons Introduction Mapping from aerial photographs can take on numerous forms and can employ either hardcopy or softcopy approaches. Traditionally, topographic maps have been produced from hardcopy stereo-pairs in a stereo-plotter device. A stereo-plotter is designed to transfer map information without distortions, from stereo photographs. A similar device can be used to transfer image information, with distortions removed, in the form of an Orthophoto. Cont.

9 Koert Sijmons Introduction Orthophotos combine the geometric utility of a map with the extra “real-world image” information provided by a photograph. The process of creating an Orthophoto depends on the existence of a reliable DEM for the area being mapped. The DEM is usually prepared photogrammetrically as well. A digital photogrammetric workstation generally provide the Integrated functionality for such tasks as generating: DEMs, digital Orthophotos, perspective views, and “fly-throughs” simulations, as well as the extraction of spatially referenced GIS data in two or three dimensions

10 Koert Sijmons Introduction

11 Koert Sijmons 60% forward overlap % side lap Flight strip 1 Flight strip 2

12 Koert Sijmons Terrain Flight line Nadir line (ground trace of aircraft) Endlap Photographic coverage along a flight strip Conditions during exposures Resulting photography

13 Koert Sijmons Flight line 1 Flight line 2 Flight line 3 Exposure station Flight paths (Photo run)

14 Koert Sijmons Focal length E O Exposure station (L) Negative d a b c e y x o Positive c’ d’ b’ a’ C D A B e’ o’ Optical axis Geometric elements of an aerial photo

15 Koert Sijmons Eustasius June Fiducial marks Message Pad Watch Altimeter Principle point

16 Koert Sijmons Photography central projection

17 Koert Sijmons Central perspective

18 Koert Sijmons Película negativo Film negative Focal length Exposure station o’ Principle point Optical axis Concepts Flying height O

19 Koert Sijmons L Principle Point Photo Map Orthogonal projectionCentral Perspective projection Geometry of Map and Photo Varied scale Relief displacement Result in: Different size, shape and location of static objects

20 Koert Sijmons Scale at sea level (0 mtr.): Scale at 50 mtr. Terrain elevation: Scale at top volcano (590 mtr.) S = scale f = focal length ( cm) H = flying height (6200 mtr.) h = local terrain height 1: : : Closer to the camera = larger scale Scale S = H – h f

21 Koert Sijmons Positive Datum f o h L H O R A A” A’ a a’ D d r Relief displacement Occurs for terrain points Whose elevation is above or below the reference Elevation (at O). Can be used for height Calculation (h): h = d H r d = 2.01 mm. H (Flying Height) = 1220 mtr. r = mm. h = mtr.

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23 Koert Sijmons o’ o Change in positions of stationary objects caused by a change in viewing position Parallax of point A Pa = x a – x’ a DATUM y x L y’ x’ L’ a b a’ b’ x’ a o x a ba o’ A B a’b’ o Pa = the parallax of point A x = The measured x coordinate of image a on the left photo a x’ = the x coordinate of image a’ on the right photo a

24 Koert Sijmons Y X Y Y X O X Y X O’ a b a’b’ x a x’ a Pa = x – x’ a a Pa = – ( ) = mm x b x’ b Pb = x – x’ b b Pb = – ( ) = mm ΔP = 12.00

25 Koert Sijmons Datum H O o O’ A f + X + Y B O A Y A A x X A h A L’ o’ f B = Air base H = Flying heightf = Focal length Pa B f H - h A = _______ Pa = parallax of point A h = Height above datum A H – h = Bf P a ____ A Also from similar triangles: LOA A x and Loa x H - h A X A _____ a x = __ f From which: L X Y x a a x a y a a’ x x’ a X A x (H – h ) a A = _________ f X A = B x a p a ____ Y A = B y a p a ____

26 Koert Sijmons X A = B x a p a ____ Y A = B y a p a ____ Parallax equations are ground coordinates of a point with respect to an arbitrary coordinate system whose origin is vertically below the left exposure station and with positive X in the direction of flight X and Y p Is the parallax of the point in question x and y are the photocoordinates of point a on the left-hand photo The major assumptions made in the derivation of these equations are that the photos are truly vertical and that they are taken from the same flying height.

27 Koert Sijmons Aerial Photo Concept Digital Orthophotos are generated from the same type of Aerial photo as conventional hardcopy Orthophotography. The difference lies in the scanning of the airphoto, converting the photo to a digital image product that will be manipulated and processed with a computer. Cont.

28 Koert Sijmons Aerial Photo Concepts The relationship between photo scale, scanning resolution and final scale must be considered. Final resolution of the Orthophoto product is based on the application that the Orthophotos are being used for, and also the limitations of disk space that may be encountered during the project. It is not always beneficial to scan an airphoto at the highest number of dots per inch (DPI), if the application does not warrant such high resolution. Cont.

29 Koert Sijmons Aerial Photo Concepts A simple equation can be used to calculate the scanning resolution necessary based on the original scale, final output pixel size and the size of the hardcopy photo. The equation is: where: p = output pixel size (cm) W = photo size (cm) r s = scanning resolution (DPI) d = Foot print size (cm) Cont. = ______ r s W p * d * 2,54 cm/inch

30 Koert Sijmons Aerial Photo Concepts Example: A photo is 9 inches (22.86 cm) across, and covers a ground distance of 8 Km. The final resolution required is 3 meter the scanning resolution in dots per inch (DPI) would be: r s = cm * 2.54 cm/inch = 296 DPI cm * 300 cm _________________ Cont.

31 Koert Sijmons Aerial Photo Concepts The scanning resolution can also be determinated from the photo scale, without having calculate the ground distance. photo scale is more commonly quoted in the aerial survey report. = ______ r s W p * d From the previous mentioned equation: we derive: r s = d W * S * 2.54 p ____ ___ = 2.54 ____ p where S = photo scale Cont.

32 Koert Sijmons Aerial Photo Concepts For example, a typical aerial survey might consist of photos at 1:4,800 scale. The desired output resolution for the orthophotos is approx. 30 cm. For cm airphoto, a reasonable scanning resolution would be: r s = _____ * * S 2.54 p = 4800 _____ 30 = 406 DPI

33 Koert Sijmons Aerial Photo Concepts The St. Eustasius demonstration dataset was flown at an average photoscale of 1:40,500 The photos are cm x cm. We want a ground resolution of 3m., so we must calculate the scanning resolution. r s = S * * 2.54 p = = DPI ____ 2.54 ____

34 Koert Sijmons Photogrammetric Triangulation What is it? - Increasing the density of whatever ground control you have; called “Control Point Extension” What does it do? - Computes coordinate values for any point measured on two or more images (tie points) - Computes positions and orientation for each camera station Cont.

35 Koert Sijmons Photogrammetric Triangulation Computes position of Each camera station - X,Y and Z (where Z is flying height) - Omega (  ) - Phi (  ) - Kappa (  )

36 Koert Sijmons    Aerial photographs   Deformations X Y Z X Y Z X Y Z

37 Koert Sijmons Photogrammetric Triangulation How do you do it? Interior Orientation Exterior Orientation Image measurements Ground Control Points (GCP)

38 Koert Sijmons Interior Orientation - Lens focal length - Origin of co-ordinate system (principal point) - Radial lens distortion Objective: Interior Orientation models the geometry inside the camera Coordinate systems - Establish the relationship between positions in the image (pixel) and the corresponding position in the camera (mm.) The coordinates of the fuducial points in the camera are known.

39 Koert Sijmons left right Principle point Aerial photographs en stereo

40 Koert Sijmons Fiducial marks Interior Orientation: Image used during demonstration Principle point Image details: Average photo scale: Scanning resolution: Ground resolution per pixel: 1:40, DPI (2.54 / 300)*405 = 3.43 m.

41 Koert Sijmons Interior Orientation Film: coordinate position are measured in microns (Image coordinate system) Digital image: coordinates positions are measured in pixels (Pixel coordinate system) Using fiducial points a linear relationship can be established between film and image coordinate postions

42 Koert Sijmons 1: : : : X and Y coordenates of the fuducial points Y X -X Principal point

43 Koert Sijmons Column line X Y Relation between Pixel coordinates (Line,Column) and Image coordinates (in the camera in millimeters) (x,y)

44 Koert Sijmons Y X 0 Col pixel 0 Lin pixel 0 A Col pixel A Lin pixel A Pixel coordinate system Image coordinate system (film) Colum line 0,0

45 Koert Sijmons Interior Orientation - Camera calibration information - Obtained from “camera calibration certificate” - Calibration elements: - Focal Length - Fiducial coordinates - Principal point location - Radial lens distortion

46 Koert Sijmons Exterior Orientation Objective: Establishing a relationship between the digital image (pixel) co-ordinate system and the real world (latitude and longitude) co-ordinate system Ground Control Points Visually identifiable Preferably on multiple images Larger image blocks need less control per image Need to be well distributed in X,Y and Z Ground control types: – Full (X,Y,Z) – Horizontal (X,Y) – Vertical (Z)

47 Koert Sijmons O:Projection centre A:Point on the ground a:Image of A on the photograph from similar triangles: O (U o, V o, W o ) colinearity condition a (U a, V a, W a ) A (U A, V A, W A ) U A -U o V A -V o U a -U o V a -V o W o -W a W o -W A

48 Koert Sijmons angles    Z (Kappa)  X (Omega)  Y (Phi)

49 Koert Sijmons What do these letters mean? Position of a point in the image: x, y Position of the corresponding terrain point: U, V, W Known after interior orientation: x PP, y PP, c From Exterior orientation: U o, V o, W o, r 11, r 12, r 13, r 21, r 22, r 23, r 31, r 32, r 33 (computed from of , ,  ) For each point in the terrain its position in the image can be computed from these two equations. (Different for the left and the right image.)

50 Koert Sijmons Resampling one pixel Center of the orthophoto- pixel in the original image “Nearest neighbour”: the value of this pixel “Bilinear”: interpolated between these 4 pixelcenters

51 Koert Sijmons Example St Eustatius: How to accurately transfer interpretation from photo to map!!! Shoreline from topographical map Aerial photo ?

52 Koert Sijmons Available: 2 digital stereo Aerial Photos at scale 1:40,000 of the Island of Sint Eustasius (Caribbean Sea) Left Right

53 Koert Sijmons Available: Topographic map at scale:1:10,000 of St. Eustasius

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55 Koert Sijmons Software: ERDAS IMAGINE 8.6

56 Koert Sijmons OrthoBASE

57 Koert Sijmons Create New Block File Working Directory Type: Block File name Sint_eustasius.blk

58 Koert Sijmons Setup of Geometric Model Frame Camera

59 Koert Sijmons Select Projection Set Projection

60 Koert Sijmons Select Projection UTM Zone 20 (Range 66W-60W)

61 Koert Sijmons Select Spheroid Name

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63 Koert Sijmons Set Horizontal/Vertical Units in: Meters

64 Koert Sijmons Set Fly Height in meters V 6200

65 Koert Sijmons Loading images Load left and right images From your working directory

66 Koert Sijmons Loading Left and Right image d:/het mooie eiland st eustasius/left img d:/het mooie eiland st eustasius/right img

67 Koert Sijmons Set up for Interior Orientation

68 Koert Sijmons Set Focal Length

69 Koert Sijmons Type: 4

70 Koert Sijmons Indicating: left.img Interior orientation for left image

71 Koert Sijmons Load left image 1 st Fiducial pointJumps automatically to next fiducial point

72 Koert Sijmons st fiducial point Set fiducial mark Coordinades 1 st. Fiducial point

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75 Koert Sijmons Measure 2nd fiducial point, as done for point 1

76 Koert Sijmons Measure 3rd fiducial point, as done for point 1 and 2

77 Koert Sijmons Measure 4th fiducial point, as done for point 1, 2 and 3

78 Koert Sijmons Should be less than 1 pixel All 4 fiducial points are measured

79 Koert Sijmons Make adjustments for the fiducial points in order to get less than 1 pixel RMSE

80 Koert Sijmons Green infill indicates, that Interior orientation has been carried out for left.image

81 Koert Sijmons Indicating: left.img Indicating: right.img

82 Koert Sijmons Interior Orientation for right image

83 Koert Sijmons Measure the 4 fiducial points for the Right image, starting with point 1,as done for the Left image

84 Koert Sijmons The measurement for the 4 fudical points are completed with less then 1 pixel RMSE

85 Koert Sijmons Both images have their interior orientation (green) Set Ground Control Points (GCPs)

86 Koert Sijmons Control Points X = Y = Z = 107 m. Coordinates: 1

87 Koert Sijmons 1 1 Control Point in map with corresponding point in left image

88 Koert Sijmons Z ValueY CoordinatesX CoordinatesPnt nr.

89 Koert Sijmons Z valueY coord.X coord.Pnt. Nr.

90 Koert Sijmons Z valueY coord.X coord.Pnt. Nr.

91 Koert Sijmons Measuring Ground Control Points (GCP’s) Set Ground Control Points (GCPs)

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93 Koert Sijmons Add 1 st. Ground Control Point (GCP)

94 Koert Sijmons 1 1 Set register mark to point 1 in the right image, according to the position of the Ground Control Point in the map 1 1 Set register mark to point 1 in the left image, according to the position of the Ground Control Point in the map Register Ground Control Point Type in: X-coordinates: Y-coordinates: Z-value: for Point 1 Click: Enter Register Ground Control Point

95 Koert Sijmons Set register mark to point 2 in the right image, according to the position of the control point in the map Set register mark to point 2 in the left image, according to the position of the control point in the map Register Ground Control Point Register Ground Control Point Type in: X-coordinates: Y-coordinates: Z-value: for Point 2 Click: Enter

96 Koert Sijmons Set register mark to point 3 in the right image, according to the position of the control point in the map Set register mark to point 3 in the left image, according to the position of the control point in the map Type in: X-coordinates: Y-coordinates: Z-value: for Point 3 Click: Enter Register Ground Control Point Register Ground Control Point

97 Koert Sijmons 4 4 Set register mark to point 4 in the left image, according to the position of the control point in the map Automatically display the Image positions of Control Points on the overlap areas of 2 images. This capability Is enabled when 3 or more Control Points have been measured 4 4 Set register mark to point 4 in the right image, according to the position of the control point in the map Type in: X-coordinates: Y-coordinates: Z-value: for Point 4 Click: Enter Register Ground Control Point Register Ground Control Point

98 Koert Sijmons Continue the same Procedure for the Remaining Ground Control Points according to map and Coordinate list

99 Koert Sijmons Click right button Control Full Change type “none” into “Full” and Change “Usage” into “Control For all GCP’s

10 0 Koert Sijmons Click: the automatic Tie Point Collection Properties icon

10 1 Koert Sijmons 50 Check to confirm that the Image Layer Used for Computation is set to 1 Check to confirm that the Initial Type radio button is set to Exterior/Header/GCP Check to confirm that the Keep All Points checkbox is off (unchecked) Click in the Intended Number of Points Per Image field and type: 50, then press Enter Click the Run button 1 Check to confirm that the Image Used radio button is set to All available

10 2 Koert Sijmons Click in the > column of Point Ids to see where tie points were placed. Tie points outside the land area have to be deleted. If the tie points needs to be Adjusted, click the Select Point icon and adjusted it in the Detail View SaveClose Activate Point 48

10 3 Koert Sijmons Triangulation Properties

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10 6 Koert Sijmons The X and Y deviations of the Coordinates are within the tolerance of 1 pixel. The image was scanned with a Ground Resolution of 3 meter The height value accuracy is Within 0.64 meter Save as…

10 7 Koert Sijmons ASCII Text File (*.txt)) St_Eustasius

10 8 Koert Sijmons Exterior orientation has been completed

10 9 Koert Sijmons Delete Tie Points with negative height values Activate Point 45, 46, 47 After Triangulation all Tie Points have X, Y, Z References

11 0 Koert Sijmons DTM Extraction

11 1 Koert Sijmons Select: Single DTM Mosaic File Chooser

11 2 Koert Sijmons DTM_ St.Eustasius OK

11 3 Koert Sijmons DTM_ St. Eustasius Type: 30 meters V Make Pixels square

11 4 Koert Sijmons DTM processing

11 5 Koert Sijmons DEM is calculated Save…

11 6 Koert Sijmons dem_st. eustasius OK

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11 8 Koert Sijmons Orthophoto generating

11 9 Koert Sijmons Orthophoto Resampling DEM DEM.IMG

12 0 Koert Sijmons Orthophoto generated

12 1 Koert Sijmons Orthophoto

12 2 Koert Sijmons DEMOrthophoto

12 3 Koert Sijmons Topographic map Orthophoto

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