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What is 3D scanning? LiDAR vs Photogrammetry

27/09/2021 thomas leclair

The creation of 3D models is booming. Indeed, it is interesting to all types of users and trades, starting with the States and the military, who have always been among the first to carry out precise maps of the territory. This database holds a considerable level of information and is used for the aviation, navy, land transport, agriculture, security, trade, territorial engineers, landscapers, architects, and even the world of simulation (video games, e-learning, etc.).

 

Today the reference remains Google Earth which has made a satellite map of the entire territory accessible to all and annually updates it. However, this 2D/3D mapping has a limited accuracy and definition (accuracy: about 5 to 10 m and resolution about 1m/px), which can be insufficient for some studies that require more finesse. Moreover, this accuracy varies according to the regions of the world. Moreover, these data are not downloadable and therefore their exploitation remains limited. There are other databases such as the IGN or Geoportal in France that are very well referenced and are accessible to all. However, this data remains in 2D and yet there is no way to get it in 3D. Moreover, the accuracy remains insufficient for the survey, inspection, engineering and architecture professions, which is why we always call on professional surveyors to have the highest level of accuracy and certification. Another problem is that the frequency of surveys does not necessarily allow a fairly fast update of the data.

Googleearth image satellite data 3d 2dphotogrammétrie photogrammetry datamodeling barcelone
Google Earth 3D, cf. Google Earth

The purpose of this article is to differentiate 3D scanning technologies and the other types of tools we currently have. There are two distinct types of technologies: LiDAR and photogrammetry.

 

LiDAR consists of a remote sensing and ranging method similar to radar, but which emits pulses of infrared light, then by measuring the return time after being reflected off nearby objects, allows millions of points to be placed correctly in 3D in space. “This detailed 3D mapping can provide information about the position, shape and behavior of objects. This technology is becoming so popular that Apple has integrated this technology into the latest Iphone 12 pro and Ipad pro. However, to guarantee a professional result, there are pro scanners such as Faro or Leica which remain the reference in the field.

 

Photogrammetry is a different technique because it consists of making measurements from photos, using the parallax obtained between images acquired from different viewpoints. “This technique relies entirely on rigorous modeling of the geometry of the images and their acquisition in order to reconstitute an exact 3D copy of reality.

drone scan 3d photogrammétrie
Captation drone, DJI Mini, Cotentin, France
Picture by Lowell Zima

A simple camera and processing software allow the reconstruction of 3D models. The drone is a very powerful tool because it can embark sensors of all kinds: LiDAR, infrared, high definition photography, etc… It allows to capture very large areas, to have freedom for aerial photography and access to areas sometimes difficult. In addition, it is geo-located with an accuracy of about 1 meter, which makes it possible to directly integrate the real position of 3D models. DJI and Parrot in France are at the forefront of this field and are revolutionizing the way we scan every year.  

As with LiDAR, this makes it possible to create clouds of millions of points that can then be meshed in 3D to reconstitute a triangulated surface (3D mesh). Photogrammetry software such as Pix4D, PhotoScan or Reality Capture allow this treatment as well as the plating of the photographic texture on the 3D model in high resolution.  These techniques are amazing and allow (depending on the sensors and software used) a millimetric reconstruction of objects, buildings or even territories while projecting their texture in ultra high resolution. 

The explosion of these new tools and processing technologies has created new jobs, such as the remote pilot who is equipped with a drone and is authorized to make administrative requests or the “data modeler”, who deals with the processing and modeling of the data captured by the drone.

nuage de points points cloud scan 3D drone photogrammétrie photogrammetry
Nuage de points, cf. Shenron Studio

 

mesh 3d maillage scan 3D drone photogrammétrie photogrammetry
Maillage 3D, cf. Shenron Studio
mesh 3d maillage scan 3D drone photogrammétrie photogrammetry texture
Maillage 3D + ortho-texture, cf. Shenron Studio

With these high-precision 3D digital models, it becomes possible for all trades to store them, work on them, exploit them and collaborate in real time.

Architects and engineers can directly take 2D/3D measurements and quickly visualize the current state of a building, calculate cubatures and position surveys for construction sites, fine-tune topography studies and simulations for the inspection, heritage and scientific professions, as well as the world of video games, which directly integrates “maps” (3D cartography).

 

 

 

Finally, it is possible to upload (load online) the models on GIS software as well as Google Earth in order to increase the level of global 3D data.

 

Sources:

Précision GG Earth:
https://fr.geofumadas.com/google-earth-will-have-more-images-avec-pixel-of-50-cms/

 

https://qastack.fr/gis/11395/spatial-resolution-of-google-earth-imagery

 

Lidar:

https://leddartech.com/fr/pourquoi-lidar/

 

Data modeling:

https://fr.wikipedia.org/wiki/Photogramm%C3%A9trie

 

https://numerisation3d.construction/fonctionnement-photogrammetrie/?v=04c19fa1e772