Introduction to Geomatics - kau _ Lecture 5... · Principles of Photogrammetry Lecture 5:...

Geomatics Department

King AbdulAziz University

Faculty of Environmental Design

قسم الجیوماتكس

Introduction to Photogrammetry

Introduction to GeomaticsGEOM 101

Ahmad Baik, Ph.D.Email: [email protected]

Week 8


Summary

Lecture 5: Introduction to Photogrammetry

I. What is Photogrammetry

II. Principles of Human Vision

III. Branches of Photogrammetry

IV. Principles of Photogrammetry


What is PhotogrammetryEtymology

Etymologically, the term photogrammetry is composed of threeGreek roots : ‘Photo’, ‘Gram’ and ‘Metry’.

* Photos: which means ‘Light’.* Graphein : which means ‘Write’ (or ‘Draw’)* Metron : which means ‘Measure’

Hence, we can deduce the etymological meaning as ‘the science ofmeasuring from photographs ’



What is PhotogrammetryASPRS Definition

The American Society of Photogrammetry and Remote Sensing(ASPRS) defines photogrammetry as ‘the science, art andtechniques of obtaining reliable information about physicalobjects and the environment. This is done through a process ofrecording, measuring, and interpreting aerial and terrestrialphotographs ’.



What is PhotogrammetryPhotogrammetry Workflow


A standard workflow of Photogrammetry contains three mainphases which are: 1) Data Acquisition, 2) PhotogrammetricProcedures and 3) Photogrammetric Products.

Data Acquisition

Film Camera

Digital Camera

Photogrammetric Procedures

Rectification

Restitution

Aero-Triangulation

Photogrammetric Products

Orthophotos

Topographic Maps

Digital Elevation Model


Principles of Human Vision


The principles of Photogrammetry come from the understandingof how Human eyes work. In fact, the lens of the eyes act like aconvex lens that produces an image of the object on the retina.The produced image, which has an inversed orientation, is thentransmitted to the brain through the optic nerve in order to beinterpreted.

ObjectRetina

Eye’s Lens

Eye




The monoscopy is the process of vision that involves only a singleeye. Although the image formed on the retina contains a hugeamount of information, the monoscopy provides only a twodimensional representation of the scene (the perception doesn’tcontain any information about the depth of the scene).

Monoscopy

Left Eye




The Stereoscopy is the process of vision that involves the two eyesat the same time. The Stereoscopy allows perceiving the thirddimension of the scene, through the brain interpretation of the twoimages that are formed on the left and right retinas.

Stereoscopy

Left Eye Right Eye




The Human brain does not make any ‘graphical’ report of therays that come from the scene. It analyses the angle between thetwo light beams (that come from one object) which are perceived byeach eye. This angle is called ‘Parallactic Angle’.

Parallactic Angle

A point which is closer to thehuman eyes has a largeparallactic angle, and pointwhich is farther has a smallerparallactic angle.

Left Eye Right Eye


Branches of Photogrammetry


There are many methods used in photogrammetry in order toextract information from photos. However, Photogrammetry may bedivided into two main groups: 1) Aerial Photogrammetry and 2)Close range (or Terrestrial) Photogrammetry.

In addition, Aerial Photogrammetry may also be classified intothree categories:

1- Analog Photogrammetry,2- Analytical Photogrammetry,3- Digital Photogrammetry,




The development ofbranches ofPhotogrammetrydepends on theadvancement andinnovation related t0the used technologies(photography,airplanes, computersand electronics).




Analog Photogrammetry is the branch of Photogrammetry thatincludes all methods and techniques to extract information fromanalog photos based on mechanical and optical methods or theircombination.

The Principle of Analog Photogrammetry is to produce in thelaboratory, and on a smaller scale, the configuration of thecamera when taking pictures in two positions. Thisconfiguration is reconstructed by using optical and mechanicalinstruments.

Analog Photogrammetry




Example of an analog instrument for Photogrammetry

Analog Photogrammetry




Analytical Photogrammetry is also based on the reconstruction ofcamera’s positions during the flight mission. However, thereconstruction is not performed mechanically.

Although the used photos are analog, the principle of AnalyticalPhotogrammetry is to reconstruct mathematically theconfiguration of cameras during the flight using computers.

Analytical Photogrammetry




Example of an analytical instrument for Photogrammetry

Analytical Photogrammetry




Digital Photogrammetry uses the same mathematical principlesas Analytical Photogrammetry. However, DigitalPhotogrammetry (in contrast to Analytical Photogrammetry) usesDigital Photos.

Digital Photogrammetry

Digital Photos may come eitherfrom scanning existing AnalogPhotos, or directly acquired fromDigital camera (see picture below).




Example of an Digital instrument for Photogrammetry

Digital Photogrammetry

Leica Photogrammetric High Resolution Scanner




Close –range (Terrestrial) Photogrammetry

Close-range (or Terrestrial)Photogrammetry uses the sametheoretical basis as AerialPhotogrammetry. In the case,the photos are taken from a very-close distance from the objectto be photographed.


Principles of Photogrammetry


Characteristics aerial photographyMarginal data of aerial photography

Fiducial marks: small registrationmarks exposed on the edges of aphotograph. The distances betweenfiducial marks are preciselymeasured when a camera iscalibrated.Roll and Photo Numbers: eachaerial photo is assigned a uniqueindex number according to thephoto's roll and frame.Geographic location, time anddate, etc.




Focal and ScaleFocal length: the distance from themiddle of the camera lens to thefocal plane (i.e. the film). Thefocal length is preciselymeasured when the camera iscalibrated.

Scale: the ratio of the distancebetween two points on a photo tothe actual distance between thesame two points on the ground.

Characteristics aerial photography




Distortion on aerial photographyThe projection of a photography is a perspective (or central)projection, because all the rays should pass through a point calledthe center of perspective. This type of projection causes animportant distortions especially for taller object on the scene.

Characteristics aerial photography




Stereoscopic coverage

The concept of Stereoscopy inphotogrammetry is one of themost important notions. It usesthe same principle of humanvision in order to extract theelevation of an object in a scene. Toretrieve the elevation from a scene ithas to be necessaryphotographed from to differentperspectives (Overlap region).

Overlap Region




Stereoscopic coverage

Overlap: is the amount by whichone photograph includes thearea covered by anotherphotograph, and is expressed as apercentage. The photo survey isdesigned to acquire 60 per centforward overlap (betweenphotos along the same flightline) and 30 per cent lateraloverlap (between photos onadjacent flight lines).




Stereoscopic restitution

The Stereoscopic restitution consists of reconstructing astereoscopic model (which will be seen by the operator) from twoimages that were taken from different angles. To do so, each eyehas to see only the corresponding image (left or right), and thehuman brain will automatically perceive the three-dimension.

Left Eye Right Eye

Left Image Right Image





There many methods used to display the corresponding image foreach eye. The most used methods are: 1) Optical Stereoscope, 2)Anaglyph (with complementary colors) and 3) Polarization(polarized filters).

Example of Optical Stereoscope





To display the two images, we use aspecial glass with twocomplementary colors (cyan andRed for example). Hence, eacheye will see only one of the twoimages.

Example of Anaglyph





To display the two images, we use aspecial glass with two differentpolarization (Horizontal andVertical for example). Hence,each eye will see only one of thetwo images.

Example of Polarization





In order to construct a Stereo Model, it is necessary to reconfigurethe position of the two images as their initial positions duringthe flight mission.

The process of Stereoscopic restitution consists of three mainphases:

1- Interior orientation2- Relative orientation3- Absolute orientation

Sometimes, relative and absolute orientation may be combined inone step called Exterior orientation.





The aim of Interior orientation is to define a Photo coordinatesystem for each Photography. This is very important in order toreconstruct the Perspective Projection of each image. To do so, weuse the fiducial marks for each photography.

Interior Orientation





The aim of Relative orientation is to the relative position of twophotographs, or a relation to another. To do so, an image is fixedand we ‘drag and rotate’ the other until finding the relative positionas the flight mission. "Drag and rotate" means to move the imagearound the axis ω (Omega), φ (Phi) and K (Kappa),corresponding to X, Y and Z.

Relative Orientation





The Absolute orientation aimsto bring the relative stereo-model constructed in theprevious phase to the groundScale, Orientation and Level.When we complete this phase,the measurement on thestereo-model will be the sameas if we were on the real field.

Absolute Orientation


Introduction to GPS

Introduction to GeomaticsGEOM 101

Reda Yaagoubi, Ph.D.Email: [email protected]

Week 9

Introduction to Geomatics - kau _ Lecture 5... · Principles of Photogrammetry Lecture 5:...

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