Photogrammetry

Photogrammetry is a simple technique that uses photographs for surveying and mapmaking. It is the science that helps in obtaining important information about the physical objects and environment through the process of recording, interpreting, and measuring the photographic images. It is a simple science of making measurements from photographs. 

In the year 1851, a French inventor by the name of Aimé Laussedat had a theoretical idea of the camera that could help in mapping but he wasn’t able to invent it. Fifty years later, in the middle of the nineteenth century, photogrammetry was invented and appeared simultaneously with the appearance of photography. A french surveyor by the name of Dominique F. Arago proposed the use of photographs to create a topographic map in the year 1840. The Prussian architect by the name of Albrecht Meydenbauer first coined the term photogrammetry in his 1867 article "Die Photometrographie."

For many centuries photogrammetry has helped us in understanding the faraway objects and the surfaces of the earth. Due to its application, its uses have been expanded over the years and have led to the birth of powerful techniques that help many industries such as engineering, medicine, construction, and many more. Imagine you want to analyze an object, photogrammetry helps in gathering the data and the measurements of the object by only analyzing the changes in the position of that object by viewing two different images. Photo is analyzed and advanced processing software is used to do the photogrammetric job. In this article, the method of photogrammetry, the science involved behind the technique, the different types of photogrammetry will be explained.

Basics of Photogrammetry 

If we break down the word photogrammetry, we can clearly understand what the word means. Photo means light, ‘gram’ means drawing and ‘metry’ means measurement. Photogrammetry could be described as the 3-dimensional coordinate measuring technique that uses the photographs as the fundamental object for measurements. Photogrammetry generally revolves around the idea of gathering information from the photos which are collections of the object. 

The fundamental concept of photogrammetry is triangulation in which multiple photos are taken(At least two) to create a line of sight that will point on the object. The photos are taken from different angles and locations which helps in making accurate calculations that will help gather the data a person is looking for. The line of sight that was created because of the data that was collected can now be mathematically inserted to produce the 3-dimensional coordinates of the points of interest. Photogrammetry helps in creating 3 d models and maps of the real world. During World War II, the use of photogrammetry increased. During World War II, special aircraft were built that were designed to carry powerful cameras which were designed for aerial photography and better camera positioning. Photogrammetry during that time was extensively used to monitor the enemy countries territory. During the Apollo mission,  photogrammetry also helped in mapping the surface of the moon.

Types of Photogrammetry

Photogramteert can be classified into two types based on the splitting the field on which the camera is located during photography. On the basis of this approach, we have Aerial photogrammetry and Close range or terrestrial photogrammetry. 

What is Aerial Photogrammetry? 

For mapping, a particular area, the most commonly used photogrammetric method is aerial photogrammetry. In aerial photogrammetry, the camera is mounted in an aircraft and is pointed vertically towards the ground. When the plan follows a flight path and by mounting the camera vertically towards the ground the camera then takes multiple overlapping photos of the ground. The multiple photos which were taken were traditionally monitored by a stereo plotter. A stereo plotter is an instrument that helps the operator or the user see two photos at once in a stereo view. The stereo plotter also helps in determining the elevation by comparing the two different photos and also helps in conducting the necessary calculations. Stereo plotters were extensively used a decade ago but now all the photos taken during aerial photogrammetry are processed by automated desktop systems. 

What is Terrestrial Photogrammetry?

In terrestrial photogrammetry or close range photogrammetry, the camera is located on the ground which is either handheld or fixed and images are taken from the fixed position on the ground in the axis of the camera is parallel to the Earth surface. The coordinates and other data of the camera are collected at the time in which the photo is taken.  Theodolites are the instruments that are used for terrestrial photogrammetry or close range photogrammetry. Terrestrial photogrammetry is non-topographic which means it is not related to the arrangement of the physical features of the area. The output of the terrestrial photogrammetry are drawings, 3D models, and measurements. cameras can also be used to measure and model buildings,  help in engineering structures, stock-piles, film sets, etc. terrestrial photogrammetry is also called as Image-Based Modeling in the computer-based community. 

What is Stereo Photogrammetry? 

Stereo photogrammetry is a technique that involves the estimation of 3D coordinates of points on an object by considering the measurements made of two or more images taken from different positions. By collecting the points obtained from the x,y, and z coordinate the image is calculated. The principles on which Stereo photogrammetry is based is stereoscopic principles which allow the user to create or enhance the illusions of the image by the means of stereopsis for binocular vision. The binocular vision follows a simple principle that says that a user can present two different images separately by the right and the left eye and then the images are combined by the viewer’s brain to give a perception of 3D vision. There are many ways such as polarization, chroma depth, stereoscopic technique, etc that help in presenting the stereoscopic pictures. Stereophotogrammetry is turning out to be one of the emerging non-contacting techniques that helps in determining the characteristics and mode shapes of both rotating and nonrotating structures.

Applications of Photogrammetry 

Photogrammetry has been used in various fields such as medicine, engineering, mapping, architecture, manufacturing, police investigation, cultural heritage, and geology.

One of the most common uses of photogrammetry is creating maps out of aerial photos. It has proven to be accurate and cost-effective. Photogrammetry allows many government construction workers and architects to take clear pictures that help them to make clear and informed decisions about the projects without spending months working on the landscape. The photogrammetry technique is very detailed as a result of which it provides an exceptional level of information about the area. 

Many archaeologists use photogrammetry to quickly make plans of large sites which are very large and complex whereas meteorologists use photogrammetry to determine the wind speed of the tornadoes when they don't have access to the weather data. 

Due to its precision, photogrammetry has made a mark in many industries such as engineering, film industries, etc. Here is the list of few places where photogrammetry has been used. 

• Engineering

  As photogrammetry is nothing but accurate measurements of images. The first industry to adapt or use this technology in engineering. While building a complex structure it is very important to have accurate measurements of everything. The planning and the execution should be perfect and because of this reason, photogrammetry is used. By using the images from drones, engineers can evaluate the sites of construction properly which ensures that everything runs smoothly without any hurdle. If a client needs to see the progress of the work, Photogrammetry is used to create perspective images and 3D renderings which helps in analyzing the current work. 

• Film and Entertainment 

Photogrammetry plays an important role in film and entertainment. Throughout many years the filmmakers have started to heavily rely on photogrammetry for 3D modelling and accurate measurements that are required for world-building for games and movies. photogrammetry has started to play a big role in various CGI movies. The 3D modelling of photogrammetry can help in bringing the planned virtual worlds like cities and other historical places with accurate measurements.  Movies such as fight club, the matrix, and games such as the battlefield have utilized the technique of photogrammetry. 

• Forensics 

Knowing all the details while solving a case is very important and photogrammetry plates an important role in the crime investigation. photogrammetry helps in documenting the precise measurements of the scenes of crime when presenting the case in front of the court. Photogrammetric lawyers are experts who are also present that are skilled at intre[retting the photo models and can also help in solving the case both inside and outside the courtroom. 

• Land Surveying 

Land surveying is a method that uses science, measurements, and technologies to determine the surface of the earth. Land surveying uses photogrammetry to take accurate images of things such as landmasses. Land surveying also uses photogrammetry to get accurate measurements of a particular object. 

• Real Estate 

We live in a society where we can get everything online. From renting a book to renting or owning a house everything is dealt with online. As a result of this many buyers are depending on an online listing to find new homes and many real estates have to create a striking visual about the various properties which they want to sell. Instead of spending thousands of rupees on an advertisement, Modern drones and the technique of photogrammetry have been used by many real estate agents to create an accurate image of the house that they want to sell or rent. The viewers or the buyers can see the 3D image of the house from all the angles and can get a clear idea of what they are looking at. 

We have learned what is photogrammetry and the applications of it. Let's see some of the related questions as well: