Thursday, October 6, 2011

Digital Photogrammetry - A Brief Overview

Digital Photogrammetry
Photogrammetry is the study of overhead images to determine topographical properties.  Digital Photogrammetry is the use of computers to ascertain the measurements of objects in these overhead images.  The images are carried out primarily from airplanes that can take overlapping photographs or videos of a given area to get full coverage of what is required.  Satellites can also be used to produce the images.

What is Digital Photogrammetry?

Digital Photogrammetry is used with photogrammetric software to calculate spatial relationships.  Most commonly used for the creation of topographical maps, it is also used in architecture, plastic surgery, manufacturing, forensic investigation and by the military forces.  The military make great use of digital photogrammetry to plan missions, track fugitives and direct missiles.

Important Variables to Digital Photogrammetry

In digital photogrammetry there are several variables that are of importance.  The first point is the necessity of the photogrammetrist to have a full working knowledge of the camera or video involved.  This is important as the type of camera, the focal length of the lens and/or the distance from the camera to the point of interest is critical.  Often a special type of camera, called a metric camera is used to take these photographs as it is calibrated to be able to take images with very minimal lens distortion.

The second point to note well when working with digital photogrammetry is the desired result that is required of the images.  Two dimensional (2D) measurements such as the height of a mountain or the width of estuary may be all that is required many projects and can be determined from single images.  However, if a three dimensional (3D) measurement is required such as the width, length and height of a building, then the process becomes a lot more detailed as it requires information from a lot more photographs.

Stereophotogrammetry - 3d Modeling

The procedure of creating 3D models is another field again, known as stereophotogrammetry.   Stereophotogrammatetrists are able to analyze several photographs taken of the same object from a variety of angles.  Common points of reference shared by the photographs or where they overlap allow them to create a digital 3D model.  These images can then be mapped together, megapixel by megapixel to create an image of measurable space in each of the three dimensions.

The third critical variable to take into account is the type of photographs used.  These are usually video or still digital camera photographs.  Videos need to be uploaded into computers to allow them to be used in digital photogrammetry.

Types of Photographs Used in Digital Photogrammetry

3d laser modeling
Two main types of photographs used are aerial and close- range photography.  Obviously aerial images are taken from a fixed video or digital camera mounted underneath an airplane.  Topographical mapping is done by using this technique.  The airplane flies over a given area of coordinates on a meandering flight path so as to enable the images to be overlapped.

Close- range or terrestrial digital photogrammetry uses images taken from closer proximity with hand held or tripod mounted cameras.  This is what allows the third dimension to be utilized- giving the means whereby 3D laser modeling of items such as buildings can be used portraying designs in development proposals.  This method is also used on movie sets when creating scenes.

In general, digital photogrammetry is a very important field to determine many factors in varied areas of applications.  Without it, it would be very difficult to create architectural images, create accurate maps, create movie scenes, direct armed warfare and to observe global changes as they occur.

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