What is Photogrammetry?

Photogrammetry is a technology of taking measurements of physical objects present in the environment, using photographs. It includes the process of recording and analyzing a three-dimension image in the two-dimension form. Photogrammetry was invented around 150 years ago in 1851 by Aimé Laussedat, he was also known as the father of photogrammetry, but this method was not in use until 50 years after its invention. This method was first used in Germany by Dr. Albrecht Meydenbauer in 1893 who was the director of the Royal Prussian Photogrammetric institute founded by him.

Types of Photogrammetry

Photogrammetry collects accurate measurements and data of the object so that one can study all the important properties and aspects of the object through photographs. With the collected data, mapping and 3D modeling of the object can be done. Photogrammetry is of three types:

• Aerial photogrammetry – In aerial photogrammetry, photos are taken with a camera mounted on an aircraft and it is lowered towards the ground so that the high-resolution pictures can be taken from the top of it. This is the most common way to map an area. It helps to find out the elevations of the ground by setting the camera positions with other objects and developing a terrain model with necessary calculations.
• Terrestrial photogrammetry- It is also called close-range photogrammetry, in this photogrammetry, the camera axis is parallel to the ground, and photos are taken from the instruments such as a theodolite, which remains fixed to the ground. The coordinate system of an object is calculated through this photogrammetry and is often performed by a skilled technician who follows the procedure of a survey.
• Space photogrammetry- This is the same as ariel photogrammetry, but it is done on a wide-angle or a larger scale. In this method, the camera is fixed either on earth’s ground or a satellite or moon. In space photogrammetry, accurate photos are taken of earth’s topography, cloud patterns, and even images of far planets by using their space-based stations.

Types of Photos

Aerial photogrammetry is the most common method used in photogrammetry. The photos captured can be classified in two forms:

• Vertical photograph- In this photograph, the camera axis is vertical as the camera is mounted on the aircraft and pointed towards the ground giving a bird’s eye view.
• Tilted photograph- In this photograph, the camera axis is somewhat vertical but a tilt occurs due to the inclination of the aircraft, which gives oblique images. In some images horizon lines are visible and in some, they are not. 

The camera lenses offer a wide-angle image in which a large area can be covered. When aerial photos are clicked, overlapping of images is done. Here, the photogrammetry software stitches them and provides the full image with accurate points and details.

Uses of Photogrammetry

Photogrammetry is an open-source method of collecting high-quality and accurate data, using the most cost-effective way for construction, industrial use, local government, architects, and so on.

Photogrammetry plays an important role in civil surveying through which one can find out the required safety measures that should be taken for the execution of a project. Photos are taken from the different locations by drone mapping, and then measurements are calculated.

In the military, photogrammetry plays a significant role in gathering the geo-locations and for a better landscape understanding by using aerial photogrammetry. Accurate three-dimensional maps are created with less human effort.

In films and entertainment, photogrammetry is widely used for reality capture. Even in virtual games, cityscapes are required which can be easily obtained by photogrammetry.

In agriculture, photogrammetry helps farmers to keep a check on crop growth, soil quality in various regions, and irrigation requirements. They can also check crop damage after a flood and storms.

This technique is used by all engineers, architects, and geoscientists and this procedure takes about 20 to 40 min to complete post-processing of the image. After that, bundle adjustments are done by aligning overlapped photographs, and then scale bars are set accordingly.

Photogrammetry Software

Photogrammetry has developed in earlier years due to the use of computers, resulting in computational photogrammetry. It has been made easier by software, which is easily accessible to a wider audience. It enables photogrammetric measurements and the production of accurate diagrams and models through the photos. General photogrammetry software are reality capture, recap, pix4D, photo modeler, context capture, and acute 3D; these are widely used terrestrial drone software. Photogrammetry software finds the intersection of light rays and calculates the point existing in 3D space.

Best Photogrammetry Software

While choosing the best software, one should first analyze what are the requirements of a project as if it can be used for 3D mapping, Aerial photos, or focus on several images, and so on. Some of the best photogrammetry software are:

• Agisoft Metashape –This software is used for various features such as triangulation, point cloud data,3D model generation, texture, and many more. It is one of the most important and used software of photogrammetry.
• Meshroom –It is open-source software that offers a complete textured 3D reconstruction of a pipeline. Here, just put an image, and the work is done.
• Dronedeploy- It is cloud-based software that captures structure-from-motion and is widely used for industrial use. It comprises two units in which one is a drone that does aerial photography by fiving multi-view of the location, and the other one unit remains on the ground that creates 3D models from the images captured by the drone. 
• Trimble lnpho- It is professional software that is widely used for geospatial or geo modeling projects. It converts aerial images to a precise point cloud and gives a wide range of modules.
• Pix4Dmapper-This software works on drone-based mapping and works best for both aerial as well as close-range images. It gives really precise 3D and 2D models and allows to render any texture or feature.

Context and Applications

Photogrammetry is basically a relation between geometrical and mathematical regeneration of rays of light that are captured in an exposure. The major usage of photogrammetry in today's world is maps. All maps are made by photogrammetry and aerial photography. Photogrammetry is studied in graduation course such as:

• Bachelors in Technology (Civil engineering)
• Masters in Technology (Civil Engineering)

Practice Problems

Q1) Which photogrammetry software is best?

1. Photosynth
2. SOCET SET
3. Agisoft metashape 
4. IMAGINE Photogrammetry

Ans. (c) Agisoft metashape, as all the other options are semi-automatic, where only agisoft metashape is fully automatic software, consequently, it is the best software.

Q2) How long does photogrammetry take?

1. 5 hours
2. 20 to 40 minutes
3. 20 to 24 hours 
4. 8 to 6 minutes

Ans. (b) 20 to 40 minutes, photogrammetry takes around 20 to 40 minutes by using a reality capture.

Q3) What are the advantages of photogrammetry?

1. Civil surveying
2. Remote sensing
3. GPS
4. GIS

Ans. (a) Civil surveying, photogrammetry is used to survey a land area by taking photographs of it.

Q4) What does photogrammetry mean?

1. Grammar correction
2. Photo editing 
3. Measurements through photographs
4. Tachometry 

Ans. (c) Measurement through photographs, photogrammetry is the measurement of coordinates in a photograph that gives the coordinates and details of a land area.

Q5) What is photogrammetry used for?

1. Remote sensing
2. Directions
3. SBC of soil 
4. Aerial survey

Ans. (d) Aerial survey, photogrammetry is used in surveying through aircraft to get the top view of the objects on the ground.

Related Concepts

• Aerial photogrammetry
• Mapping
• Drone photography
• Civil surveys
• Geoinformatics