LO1: Describe key elements of photogrammetry and its applications
Discuss the key developments in Photogrammetry.
The origin of Photogrammetry goes back as far as1480, when Leonardo da Vinci developed, the concept of perspective and projective geometry
Pinhole image or camera obscura
The first use of Photogrammetry was by the French geodesist Arago using a process called Daguerreotype
Frenchman Laussedat referred to as the father of photogrammetry" was the first person to use terrestrial photographs for topographic map compilation
Airplane invented by Wright Brothers
Compare the methods of traditional and digital Photogrammetry.
• Image acquisition/recording
• Image orientation and stereo-model generation
• Stereo-plotting that is object measurement inside the generated stereo-mode
• Eventual orthoimage generation.
• the digital all functions are gathered within a computer where they are expressed through software.
• This transformation requires a certain level of complexity of the software itself and hardware's improved count skills, both for processing and visualization.
• Sensor: CCD AND CMOS
Explain five Photogrammetry applications used in different fields
1 . Mapping
All kind of maps whether Large, small scale can be created by photogrammetric techniques. Most common use is to produce hardcopy topographic map.
2 . Earthwork Calculations
Earthwork calculations with help of design map or directly from absolutely oriented models on stereo plotting instruments.
3. Medical sciences
» Alignment of MRI scans over time.
» Determination of root canal curvatures before and after canal preparation.
5 . Robotic Technology
Describe the 2 types of photographs based on orientation of the camera.
LO2: Explain the requirements and geometry for vertical aerial photographs.
Illustrate the geometric principle of vertical aerial photography with a labelled diagram.
Explain all of the terms used in the above diagram.
• Exposure station (o)The point in the atmosphere occupied by Centre of camera lenses at instance of photography.
• Focal length: The distance between the lens and the image sensor.
• Fiducial marks: efference marks rigidly connected with camera lens through camera body.
• Camera axis: Line perpendicular to focal plane and passing through perspective center
Explain why the purpose of photography is an essential element of a flight plan.
» first stage is requiring planning of aerial photography. The output for a successful photography mission is to obtain an excellent quality aerial photograph. Therefore, the detailed specifications of the aerial photography mission are very important for mapping.
Describe the factors that can affect the quality of aerial photographs during a flight.
LO3: Describe the types of aerial camera used in photogrammetry.
1. Lens Assembly
; 3.5, 6, 8.25 and 12 inches are typical focal lengths. The lenses of aerial systems have the focus fixed at infinity.
2. Focal Plane;
this is a perfectly perpendicular plate aligned with the axis of the lens, a vacuum system is used to fix the film to the plate so the focal plane is perfectly flat during exposure.
3. Lens Cone:
this holds the lens and filter, and covers the front part of the camera preventing light from leaking into the camera body.
encloses the camera, the mounting bolts and stabilization mechanism.
5. Drive Assembly;
the guts of the camera, the winding mechanism, shutter trigger, the vacuum pressure system and motion compensation.
6. Film Magazine;
holds the roll of unexposed film, advances the film between exposures, holds the film in place and winds up the exposed film.
Describe the components of a frame aerial camera.
Explain three ways in which a digital aerial camera differs from a frame aerial camera. DIGITAL AERIAL CAMERA
Faster turnaround time.
Greatly improved radiometric resolution.
Increased accuracy of photogrammetry measurements.
FRAME AERIAL CAMERA
Aerial camera systems also have a mounting bracket, power supply, vacuum lines, heating jackets, filters, forward motion compensation (FMC) and an Inertial Motion Unit (IMU).
Also, part of the system is a viewfinder for targeting the camera, an interval meter that determines the rate at which exposures are taken (the amount of overlap) as the plane flies along the flight path, a navigation control system and an exposure control system.
Computers have assumed many of these tasks which were once manual/mechanical. Global Positioning Systems (GPS) are now integrated into the camera system to provide very precise in- flight positional control
Explain terms of Ground Sampling Distance (GSD), pixel, Charge Couple Device (CCD)
- GROUND SAMPLING DISTANCE: The Ground Sampling Distance (GSD) is the distance between two consecutive pixel centres measured on the ground. The Ground Sampling Distance is the distance, mostly in centimetre units, between the centres of two neighbouring pixel in the image on the ground. As bigger the number of the image GSD, the lower the spatial resolution of the image and the less visible details. The GSD is related to the altitude of flight: the higher the flight altitude, the bigger the GSD number.
- PIXEL: A pixel is the smallest unit of a digital image or graphic that can be displayed and represented on a digital display device. A pixel is the basic logical unit in digital graphics. Pixels are combined to form a complete image, video, text, or any visible thing on a computer display. A pixel is also known as a picture element (pix = picture, el = element).
- CHARGE COUPLE DEVICE (CCD): AERIAL CAMERAS A Charge-Coupled Device (CCD) is a sensor of recording images in digital cameras the number usually ranges from 0 (no light) to 65,535 (very intense light) It consist an integrated circuit containing an array of linked, or coupled, capacitors acting as many small pixels. The light falling on a pixel is converted in to a charge pulse which is then measured by the CCD electronics and represented by a number.
Describe three types of image formats used for digital aerial photographs.
1. JPEG (or JPG) - Joint Photographic Experts Group
2. BMP - Bitmap Image File
3. PNG - Portable Network Graphics
LO4: Explain the different orientation methods performed for aerial photographs
Define the terms "interior orientation" and "exterior orientation". Interior orientation
Matching the camera geometry with the image geometry (Camera internal coordinate system and the image coordinate system). Camera calibration data can be used relate camera setting with the image file.
The process establishing the relationship between image coordinate system and ground coordinate system (Real world or Exterior).
All the photographs are somewhat tilted and this tilt has to be calculated in the model to be able to derive useful measurements from aerial photos.
There are six elements of EO that express the spatial location and angular orientation of the tilted photograph.
1) X,Y,Z - the three dimensional coordinate of the aircraft (camera) at the moment of exposure.
2) Omega, phi, and kappa of the camera at the moment of exposure.
Compare absolute orientation with relative orientation.
The purpose of Relative Orientation is to recreate the stereo model of the terrain in a smaller scale such that parallax is minimised.Chose six readily discernible image points approximately in the positions shown below:
• The process of scaling and leveling of the model using available ground control points is known as Absolute Orientation.
• The purpose is to bring the model to the desired scale and introduce the ground control information.
• It is necessary that interior and relative orientation of the model must be free from errors and model deformations/distortions.
• Seven parameters, 3 shifts, 3 rotations and one scale are involved in AO.
Explain direct and indirect orientation. direct orientation.
Direct orientation uses a high-grade Inertial Measurement Unit (IMU) and an optional Global Navigation Satellite System (GNSS) receiver.
It provides an absolute orientation to a continuous ground reference with a high level of accuracy.
Indirect orientation uses traditional photogrammetric orientation methods.
Well distributed Ground Control Points (GCP) and applying geometric constraints such as collinearity equations between the images points and object points.