Photogrammetry

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Photogrammetry is the practice of determining the geometric properties of objects from photographic images. Photogrammetry is as old as modern photography and can be dated to the mid-nineteenth century.

In the simplest example, the distance between two points that lie on a plane parallel to the photographic image plane can be determined by measuring their distance on the image, if the scale (s) of the image is known. This is done by multiplying the measured distance by 1/s.

Algorithms for photogrammetry typically express the problem as that of minimizing the sum of the squares of a set of errors. This minimization is known as bundle adjustment and is often performed using the Levenberg–Marquardt algorithm.

Contents

Photogrammetric methods [edit]

Georg Wiora's data model of photogrammetry [1]

Photogrammetry uses methods from many disciplines, including optics and projective geometry. The data model on the right shows what type of information can go into and come out of photogrammetric methods.

The 3D co-ordinates define the locations of object points in the 3D space. The image co-ordinates define the locations of the object points' images on the film or an electronic imaging device. The exterior orientation of a camera defines its location in space and its view direction. The inner orientation defines the geometric parameters of the imaging process. This is primarily the focal length of the lens, but can also include the description of lens distortions. Further additional observations play an important role: With scale bars, basically a known distance of two points in space, or known fix points, the connection to the basic measuring units is created.

Each of the four main variables can be an input or an output of a photogrammetric method.

Photogrammetry has been defined by the American Society for Photogrammetry and Remote Sensing (ASPRS) as the art, science, and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring and interpreting photographic images and patterns of recorded radiant electromagnetic energy and other phenomena.[1]

Integration [edit]

Photogrammetric data with dense range data from scanners complement each other. Photogrammetry is more accurate in the x and y direction while range data are generally more accurate in the z direction. This range data can be supplied by techniques like LiDAR, laser scanners (using time of flight, triangulation or interferometry), white-light digitizers and any other technique that scans an area and returns x, y, z coordinates for multiple discrete points (commonly called "point clouds"). Photos can clearly define the edges of buildings when the point cloud footprint can not. It is beneficial to incorporate the advantages of both systems and integrate them to create a better product.

A 3D visualization can be created by georeferencing the aerial photos and LiDAR data in the same reference frame, orthorectifying the aerial photos, and then draping the orthorectified images on top of the LiDAR grid. It is also possible to create digital terrain models and thus 3D visualisations using pairs (or multiples) of aerial photographs or satellite (e.g. SPOT satellite imagery). Techniques such as adaptive least squares stereo matching are then used to produce a dense array of correspondences which are transformed through a camera model to produce a dense array of x, y, z data which can be used to produce digital terrain model and orthoimage products. Systems which use these techniques, e.g. the ITG system, were developed in the 1980s and 1990s but have since been supplanted by LiDAR and radar-based approaches, although these techniques may still be useful in deriving elevation models from old aerial photographs or satellite images.

Applications [edit]

Video of a 3d model of Horatio Nelson bust in Monmouth Museum, produced using photogrammetry.
Gibraltar 1 Neandertal skull 3d wireframe model, created with 123d Catch.

Photogrammetry is used in different fields, such as topographic mapping, architecture, engineering, manufacturing, quality control, police investigation, and geology, as well as by archaeologists to quickly produce plans of large or complex sites and by meteorologists as a way to determine the actual wind speed of a tornado where objective weather data cannot be obtained. It is also used to combine live action with computer-generated imagery in movie post-production; The Matrix is a good example of the use of photogrammetry in film (details are given in the DVD extras).

This method is commonly employed in collision engineering, especially with automobiles. When litigation for accidents occurs and engineers need to determine the exact deformation present in the vehicle, it is common for several years to have passed and the only evidence that remains is crime scene photographs taken by the police. Photogrammetry is used to determine how much the car in question was deformed, which relates to the amount of energy required to produce that deformation. The energy can then be used to determine important information about the crash (such as the velocity at time of impact).

Stereophotogrammetry [edit]

A more sophisticated technique, called stereophotogrammetry, involves estimating the three-dimensional coordinates of points on an object. These are determined by measurements made in two or more photographic images taken from different positions (see stereoscopy). Common points are identified on each image. A line of sight (or ray) can be constructed from the camera location to the point on the object. It is the intersection of these rays (triangulation) that determines the three-dimensional location of the point. More sophisticated algorithms can exploit other information about the scene that is known a priori, for example symmetries, in some cases allowing reconstructions of 3D coordinates from only one camera position.

Current suite of software [edit]

Platform Standalone / Plugin Automatic modelling Scalability Data source Inception Vendor / creator Guide price
VI3DIM Unknown Standalone Yes Yes, video video 2010 Vi3Dim $20–$395
SMART3DCAPTURE Unknown Standalone Yes Yes, multiple images Images 2011 ACUTE3D N/A
ARC3D Web-based Standalone Yes Yes, multiple images Images 2005 KU Leuven Free
Pixdim Unknown Plugin Yes Yes, 1, 2 and multiple images Images - Qualup SAS $1100
RhinoPhoto Unknown Plugin Yes Yes, multiple images Images - Qualup SAS $1100
PhotoSculpt Unknown Standalone Yes No, 2 images only Images - Hippolyte Mounier $99
PhotoModeler Unknown Standalone Yes Yes, multiple images Images 1994 Eos Systems $1145
4e Software Unknown Standalone Yes Yes, multiple images Images 2012 4e Software $1000
ImageModeler Unknown Standalone No Yes, multiple images Images 2009 Autodesk Subscription benefit
3D VIA Unknown Standalone No Yes Images
Match Photo See SketchUp Plugin/feature (SketchUp) No Yes, multiple images Images - Trimble Navigation
PhotoSketch Unknown - Unknown Unknown - - Brainstorm Technology LLC $350
3D pup-up Unknown Standalone No Single image Image 2005 Carnegie Mellon University non commercial
Yodel Unknown Standalone Limited Yes, multiple images Images 2011 Lidar Pacific Corporation $499
VideoTrace Unknown Tethered Beta No Yes, multiple images Images/Video 2011 Australian Center for Visual Technology (AVCT), PunchCard Beta Tester Only
123D Catch (Beta) Unknown Standalone Yes Yes, multiple images Images/Video 2011 Autodesk Free download
Hypr3D Web-based Standalone Yes Yes, multiple images Images/Video 2010 Viztu Technologies Free
ELCOVISION 10 Unknown Standalone/Plugin Yes Yes, multiple images Images 1986 PMS AG, Leica Geosystems 2000
PhotoScan Unknown Standalone/Plugin Semi-automatic Yes, multiple images Images 2010 Ocali, Inc. $999
PhotoScan Unknown Standalone Yes Yes, multiple images Images 2010 Agisoft $179/3499
DroneMapper Web-based Standalone Yes Yes, multiple images Aerial Images 2012 DroneMapper $20 per km2
StereoScan Unknown Standalone Yes 2 images only Images 2010 Agisoft Free
My3DScanner Web-based Standalone Yes Yes, multiple images Images 2010? My3DScanner Free
PHOV Web-based Standalone Yes Yes, multiple images Images 2010 XLAB Free
Enwaii Windows/Linux Standalone/Plugin (Maya) No Yes, multiple images Images/Video 2008 Banzai Pipeline Ltd N/A
Mementify iOS Standalone Yes Yes, multiple images Images 2012 Tretja dimenzija, XLAB Free
WebDLT Unknown Standalone No Yes, multiple images Images 2012 B. Molnar, BME FMT Free

See also [edit]

References [edit]

  1. ^ ASPRS online

External links [edit]

Look up photogrammetry in Wiktionary, the free dictionary.
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