1.
What is photogrammetry? <ul><li>Photos – light Gramma – to draw Metron – to measure </li></ul><ul><ul><li>“ Photogrammetry is the technique of measuring objects from photographs” </li></ul></ul><ul><li>“ 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.” </li></ul><ul><li>Two distinct types of photogrammetry : </li></ul><ul><ul><li>Aerial / spaceborne photogrammetry </li></ul></ul><ul><ul><li>Close range photogrammetry </li></ul></ul><ul><li>Remember this : Photogrammetry is the metric interpretation of image data </li></ul>

2.
Photogrammetry portrayed as systems approach. The input is usually referred to as data acquisition, the “black box&quot; involves photogrammetric procedures and instruments; the output comprises photogrammetric products.

4.
What is photogrammetry? <ul><li>Topographic photogrammetry </li></ul><ul><li>Used for mapping Earth or planets </li></ul><ul><li>Imaging system is based on an aircraft or spacecraft </li></ul><ul><li>Target is the ground surface </li></ul><ul><li>Image data is processed to create new spatial information products </li></ul><ul><li>Close range photogrammetry </li></ul><ul><li>Used for industrial measurement </li></ul><ul><li>Imaging system is handheld </li></ul><ul><li>Target is the object being measured </li></ul><ul><li>Image data is processed to make precise measurements </li></ul>

5.
What can photogrammetry do? <ul><li>The simple answer: make accurate 2D and 3D measurements </li></ul><ul><li>Information required: images and sensor (camera) parameters </li></ul><ul><li>Close range photogrammetry: 3D only </li></ul><ul><li>Topographic photogrammetry: 2D and 3D, depending on specific application </li></ul>Single photograph + Sensor parameters = 2D measurement Multiple photographs + Sensor parameters = 3D measurement

6.
WHY PHOTOGRAMMETRY <ul><li>VERY PRECISE </li></ul><ul><li>TIME EFFECTIVE </li></ul><ul><li>COST EFFECTIVE </li></ul><ul><li>BASED ON WELL ESTABLISHED AND TESTED ALGORITHMS. </li></ul><ul><li>LESS MANUAL EFFORT </li></ul><ul><li>MORE GEOGRAPHIC FIDELITY </li></ul>

7.
Cont…… <ul><li>Corrects all sorts of distortions. </li></ul><ul><li>provide a reasonable geometric modeling alternative when little is known about the geometric nature of the image data. </li></ul><ul><li> provide an integrated solution for multiple images or photographs simultaneously </li></ul><ul><li>achieve a reasonable accuracy without a great number of GCPs </li></ul><ul><li>create a three-dimensional stereo model or to extract the elevation information </li></ul>

14.
PHOTOGRAMMETRY – Functional Details

15.
Types of photographs

16.
Image Requirements <ul><li>A block should have at least one pair of images (Satellite or Photo) which overlap: </li></ul>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 <ul><ul><li>Pushbroom Sensors - data is collected along a scan line, each scan line has it's own perspective center. </li></ul></ul>Perspective Centers

20.
Camera and Sensor Types <ul><li>Cameras </li></ul><ul><ul><li>Frame Camera </li></ul></ul><ul><ul><li>Digital Camera </li></ul></ul><ul><ul><li>Video Camera (Videography) </li></ul></ul><ul><ul><li>Non-Metric Camera (35m, Medium and Large Format Cameras) </li></ul></ul><ul><li>Pushbroom Sensors </li></ul><ul><ul><li>Generic </li></ul></ul><ul><ul><li>Spot </li></ul></ul><ul><ul><li>IRS-1C </li></ul></ul>

21.
Stereo aerial photography

22.
Photogrammetry and remote sensing <ul><li>Photogrammetry -> metric exploitation of imagery </li></ul><ul><li>R emote sensing -> thematic exploitation of imagery </li></ul><ul><li>SPOT (French RS satellite) broke down the barriers in the 1980’s and 1990’s with: </li></ul><ul><ul><li>digital linescanner </li></ul></ul><ul><ul><li>stereo imaging capability </li></ul></ul><ul><ul><li>high quality optics and orbital model </li></ul></ul><ul><ul><li> suitable for regional stereo mapping and remote sensing </li></ul></ul><ul><li>Ikonos and Quickbird (launched recently) provide high resolution stereo imagery  suitable for large scale mapping and remote sensing </li></ul><ul><li>Next step: digital aerial frame cameras </li></ul>

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 <ul><li>Stereo data can be collected on same orbit, or different orbits (beware of changes) </li></ul><ul><li>Satellite may have to be rotated to point sensor correctly </li></ul><ul><li>Optimum base to height ratio is 0.6 to 1.0 </li></ul><ul><li>Atmospheric effects (refraction, optical thickness) become more significant at higher look angles </li></ul>Different orbits Same orbit

25.
Stereo satellite imagery

26.
SPOT <ul><li>1 panchromatic, 3 multispectral channels </li></ul><ul><li>Panchromatic pixel size of 10m </li></ul><ul><li>Multispectral pixel size of 20m </li></ul><ul><li>Good for relief mapping at 1:50000 </li></ul>

27.
High resolution satellites <ul><li>Ikonos (SpaceImaging) </li></ul><ul><li>1m panchromatic and 4m multispectral imagery (NIR, R, G, B) </li></ul><ul><li>11 bit dynamic range </li></ul><ul><li>Camera specifications not available </li></ul><ul><li>Quickbird (Digital Globe) </li></ul><ul><li>0.61m panchromatic and 2.44m multispectral imagery (NIR, R, G, B) </li></ul><ul><li>11 bit dynamic range </li></ul><ul><li>Camera specifications available </li></ul>

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 <ul><li>The computer replaces some expensive optical and mechanical components. </li></ul><ul><li>The resulting devices were analog/digital hybrids. </li></ul><ul><li>Analytical aerotriangulation, analytical plotters, and orthophoto projectors were the main developments during this phase. </li></ul><ul><li>Outputs of analytical photogrammetry can be topographic maps, but can also be digital products, such as digital maps and DEMs </li></ul>

30.
Digital Photogrammetry <ul><li>Digital photogrammetry is applied to digital images that are stored and processed on a computer. </li></ul><ul><li>Digital photogrammetry is sometimes called softcopy photogrammetry. </li></ul><ul><li>The output products are in digital form, such as digital maps, DEMs, and digital orthophotos saved on computer storage media. </li></ul>

31.
<ul><ul><li>Single or pairs of digital images are loaded into a computer with image processing capabilities. </li></ul></ul><ul><ul><li>Images may be from satellite or airborne scanners, CCD cameras or are conventional photographs captured by a line scanner. </li></ul></ul><ul><ul><li>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. </li></ul></ul>DIGITAL PHOTOGRAMMETRY

32.
<ul><ul><li>Creating a 3-D model or map is a straight and linear process that includes several steps- </li></ul></ul><ul><ul><li>Sensor model defenition </li></ul></ul><ul><ul><li>Ground Control Point (GCP) measurement </li></ul></ul><ul><ul><li>Automated tie point collection </li></ul></ul><ul><ul><li>Block bundle adjustment (i.e. Aerial Triangulation) </li></ul></ul><ul><ul><li>Automated DEM extraction </li></ul></ul><ul><ul><li>Ortho-rectification </li></ul></ul><ul><ul><li>3-D feature collection and attribution </li></ul></ul>DIGITAL PHOTOGRAMMETRIC WORKFLOW

33.
Applications of Photogrammetery <ul><li>Topographic mapping </li></ul><ul><li>Creation of value added products: </li></ul><ul><ul><li>Orthoimages </li></ul></ul><ul><ul><li>Digital Elevation Models </li></ul></ul><ul><ul><li>Virtual landscapes </li></ul></ul><ul><li>Nadir imagery is essential for mapping </li></ul><ul><li>Overlap and sidelap is required to give 3D information </li></ul>

34.
Example products: maps

35.
Example products: DTMs

36.
Example products: Virtual landscapes

38.
DTMs <ul><li>Sources of terrain models </li></ul><ul><ul><li>Stereo photogrammetry </li></ul></ul><ul><ul><li>Interferometric radar </li></ul></ul><ul><ul><li>Stereo radar </li></ul></ul><ul><ul><li>Laser scanning </li></ul></ul><ul><ul><li>Digitising maps </li></ul></ul>

39.
Contour digitizing <ul><li>Digital terrain model – Digitizing contour maps </li></ul><ul><li>Two step procedure: click on the contours, then grid the data </li></ul><ul><li>Liable to error if the DEM spacing grid is too large </li></ul>

40.
Contour digitizing

41.
Contour map

42.
Radar mapping from space <ul><li>Two methods of topographic mapping using synthetic aperture radar (SAR): </li></ul><ul><ul><li>Stereo imaging ( radargrammetry ) </li></ul></ul><ul><ul><li>Radar interferometry </li></ul></ul><ul><li>Advantages of Radargrammetry: </li></ul><ul><ul><li>24 hour imaging </li></ul></ul><ul><ul><li>Physics of the imaging process is well understood </li></ul></ul><ul><ul><li>Radar relief mapping at 1:50000 is possible </li></ul></ul><ul><li>Disadvantages of Radargrammetry : </li></ul><ul><ul><li>Radar images have significant geometric distortions </li></ul></ul><ul><ul><li>Shadow and layover caused by relief </li></ul></ul><ul><ul><li>Radiometric interpretation is difficult </li></ul></ul>

43.
Radar mapping from space

44.
Stereo radar imagery

45.
DEM

46.
Stereo photogrammetry

47.
Airborne laser scanning <ul><li>Digital terrain model generation – airborne laser scanning </li></ul><ul><li>Laser pulse is emitted from the sensor – return journey time is measured, giving distance between sensor and target </li></ul><ul><li>Location of the sensor is determined by GPS </li></ul><ul><li>Therefore target can be located </li></ul><ul><li>Significant post processing is required: </li></ul><ul><ul><li>Data thinning </li></ul></ul><ul><ul><li>Gridding </li></ul></ul>

48.
LIDAR data Horizontal resolution: 2m Vertical accuracy: ± 2cm

50.
Modelling building and topological structures <ul><li>Two main approaches: </li></ul><ul><ul><li>Digital Elevation Models (DEMs) based on data sampled on a regular grid (lattice) </li></ul></ul><ul><ul><li>Triangular Irregular Networks (TINs) based on irregular sampled data and Delaunay triangulation </li></ul></ul>

51.
DEMs and TINs DEM with sample points TIN based on same sample points

52.
Advantages/disadvantages <ul><li>DEMs: </li></ul><ul><ul><li>accept data direct from digital altitude matrices </li></ul></ul><ul><ul><li>must be resampled if irregular data used </li></ul></ul><ul><ul><li>may miss complex topographic features </li></ul></ul><ul><ul><li>may include redundant data in low relief areas </li></ul></ul><ul><ul><li>less complex and CPU intensive </li></ul></ul><ul><li>TINs: </li></ul><ul><ul><li>accept randomly sampled data without resampling </li></ul></ul><ul><ul><li>accept linear features such as contours and breaklines (ridges and troughs) </li></ul></ul><ul><ul><li>accept point features (spot heights and peaks) </li></ul></ul><ul><ul><li>vary density of sample points according to terrain complexity </li></ul></ul>

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 <ul><li>DEMs allows automated modeling of hydrology </li></ul><ul><li>Hydrologic modeling is a process that begins with a DEM </li></ul><ul><li>Types of models: flow direction, flow accumulation, watershed delineation, and flow length </li></ul>

56.
Flow Direction <ul><li>Calculates flow direction for every cell in the GRID </li></ul><ul><li>Based on direction of steepest slope in local neighborhood </li></ul>1 2 4 8 16 32 64 128

57.
Flow Accumulation <ul><li>Based on flow direction grid </li></ul><ul><li>Creates a grid of accumulated flow to each cell </li></ul><ul><li>Can be used to create a stream network </li></ul>

58.
Flow Accumulation -> Streams <ul><li>Use a conditional statement to create a stream network from a flow accumulation grid </li></ul><ul><li>streams =con (flow > 100, 1) </li></ul>

59.
Delineating Watersheds <ul><li>Determines the contributing area above a set of cells in a grid </li></ul><ul><li>Needs a flow direction grid and sources </li></ul>

60.
Flowlength <ul><li>Calculates distance along a flow path for each cell </li></ul><ul><li>Goes either upstream (to the nearest ridge) or downstream (to the nearest sink or outlet) </li></ul><ul><li>Primary use is to determine the length of the longest flow path in a basin </li></ul>

61.
Visibility Analysis <ul><li>Requires: </li></ul><ul><ul><li>DEM </li></ul></ul><ul><ul><li>Viewpoint/s </li></ul></ul><ul><li>What it tells you: </li></ul><ul><ul><li>Line of sight </li></ul></ul><ul><ul><li>Viewshed </li></ul></ul><ul><ul><li>Combined Viewshed </li></ul></ul><ul><ul><li>Cumulative Viewshed </li></ul></ul>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