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Point Cloud Data from Photogrammetry Techniques

Unlike the earlier periods engineers and architects do not use the conventional 2D drawings rather they use the 3D models in default. The need for advancement in the way we constructed was catered by the rapid growth in technology. One such technological advancement that has revolutionized the way we construct is the technique of Building Information Modeling (BIM). BIM can, in short, be defined as a data-rich 3D model of a subject.

This article will give you a broad outline on what point cloud and photogrammetry are and why are they so important to the AEC industry.

What is a Point cloud in the construction industry?

A collection of data points defined by a given coordinates system is called a Point cloud. In a 3D coordinate system, a point cloud may define the as-built shape of a real or created system. When it comes to the AEC industry most 3D modelling techniques require 3D CAD data. Often the subjects of modelling are real objects for which no 3D CAD data exists. This is where the advantage of point cloud kicks in. Point cloud data is used in the AEC industry to create 3D meshes and other models which are to be integrated with the data-rich 3D BIM model. A point cloud data can be obtained from

  1. 3Dscan method
  2. Laser scanning
  3. Structured light scanning
  4. Photogrammetric method

In the 3D scan method, the point cloud data is obtained by moving the moving the laser head or the structured light cameras relative to the object to be scanned for point clouds of the object. Though 3D scans have higher resolution compared to photogrammetric methods, photogrammetric methods are preferred owing to the less cost incurred, easy handling of the point cloud data and less processing time to align point clouds compared to 3D scan methods.

Now that you know why photogrammetric methods are widely used so let’s emphasize more on photogrammetric methods in this article.

What is the Photogrammetric method?

Photogrammetry can be defined as the method of using two or more photographs taken from different locations for obtaining 3D spatial dimensions. The basic principle of working of photogrammetry is the parallax theory. The parallax obtained images taken from different points of view is used to record complex 2D and 3D fields in photogrammetry method. This process collects the details regarding the shape, the volume, and the depth of the subject being scanned.

How is a point cloud is obtained from 2D photographs?

There are a few steps involved in the process of extracting point cloud data from a series of photographs.

  1. Feature recognition: Individual photographs are analyzed and features which are invariant to scale and rotation are used to align the photos.
  2. Feature matching: Using the various algorithm available, photographs are searched for feature matching.
  3. Aligning of cameras: By minimizing the error between distances on images and expected distances for cameras, the coordinates of the cameras with respect to each other are calculated.
  4. Point cloud construction: Point cloud construction is done after cameras are aligned.

The prominent photogrammetric software packages:

It is not an easy task to choose the right photogrammetric software. The software has to be chosen based on

  • How many images need to be uploaded?
  • Are you focusing on aerial images?
  • How experienced you are?

Once you have found answers to these questions you can choose the right from the following list of software packages.

  1. Agisoft Photoscan: A stand-alone software with many interesting features like photogrammetric triangulation, point cloud data, measurements for distances, volumes and areas, 3D model generation and textures. Users can choose between a professional version or standard version.
  2. Autodesk 123D Catch: A mobile application specifically for beginners. It has an easy interface to turn the 2D photographs into a 3D You can opt for this application depending on how complex your project is.
  3. Visual SFM: A easily usable 3D reconstruction tool, you will just have to add your images, match them and make the automatic reconstruction. Much of the process is automated so this software can be the apt one for beginners.
  4. Colmap: This software is for professional. It has a GUI and a command line interface you can use the convenient one for you. You can find out more about this software at https://www.youtube.com/watch?v=P-EC0DzeVEU&feature=youtu.be. 

These are the less complex software for a photogrammetric method for developing a point cloud. The other major software package includes 3DF ZEPHYR, AutoDesk ReCap Pro, Context capture, Reality capture, Inpho, Pix4Dmapper and Photomodeler Pro 5.

Photogrammetry method compared to 3D scan is quick and efficient in extracting 3D point cloud data used to create CAD models. Being cost effective and fast apart from having matured and robust algorithms to extract data are the reasons for its wide acceptance. 

Author Bio: K. Shakti Prasad is a budding content writer working with Advenser engineering services. He has more than 5 years of experience in working as a freelance writer for various blogs and websites. Apart from writing he is a travel enthusiast and has a keen interest in music.