The 3D scanning works can be of great help when thinking about a reconstruction of this piece of art, particularly the work of Andrew Tallon. Former art professor at the University of Vassar in the United States, he digitized the entire cathedral in 2013.
"I wanted to know what the builders of the time were thinking, to understand how these buildings were built, how they are structurally located."
.Andrew Tallon para National Geographic, 2015
To "see through" the walls of the monument, Andrew Tallon used a laser and a spherical camera, which allowed to create an ultra-precise 3D map. This map will compare the state of the cathedral before and after the fire. You can also use the 3D scan provided by companies like Iconem. Work to analyze the damage and then accompany the restoration if possible. For its part, Iconem uses drones to take photos and photogrammetry that allows to locate each of the shots in space. Of course, the reconstruction work will not consist of rebuilding the Arrow with plastic to appear again in the Parisian sky as soon as possible. For these classified buildings, it is a complete work of careful restoration and respect that will have to be done, but for some elements not visible or less essential, 3D printing can be useful. The technique has already been used previously in some reconstructions for the replica of some too damaged sculptures.
The point cloud is the first three-dimensional result obtained from a laser survey and constitutes an impressive tool for the 3D handling and viewing of a structure. The plots can contain billions of points and enable a survey accuracy of up to 1 mm, thus surpassing surveys performed in a more conventional manner.
The experts in the field of surveying create their point clouds using high-end laser-scanner technology, combining performance, accuracy and rapidity. The virtual model created from this database provides the commissioner with all of the building’s dimensions, whether linear, surface or indeed volume measurements. It is also possible to create a video film from the point cloud.
The three primary components of laser surveying are acquisition, assembly, and sectioning.
Acquisition
There are two primary means to measure distance with a laser.- a) Calculating the flight time for a laser pulse to be sent, reflected from a surface and returned; and b) Calculating the phase shift induced in a sinusoidally encoded beam after travel, reflection, and return. In a typical scanner the laser beam is distributed over a range of 360 degrees horizontally and 270 degrees vertically by a rotating mirror, and acquires the distance between itself and every surface that it can see at a rate that can approach one million measurements per second. The result is what is called a point cloud.
The scanning resolution is a key consideration. Scanning with lower point density will take less time, but with too few points the details of the building will be impossible to reconstruct from the data. While an individual cloud will supply a great deal of information, it is but a single viewpoint; to produce a survey of sufficient density and to minimize occlusions it is necessary to displace the scanner.
Assembly
Once the desired stations and requisite control points are acquired the data must be registered — that is, assembled by computer. The software undertakes a series of interpolations to create a match among the various control points, or constraints, with the least error. It is often necessary to suppress certain constraints.
Sectioning
Once the data is recorded, sections, plans and views can be created by limiting the visible points. It graduates in color according to the elevation. Because the scanner generates points, not planes, all surfaces are transparent.
In a similar way, a section made with these methods can reveal information about the building with far greater clarity than could be had with the conventional tools of steel tape, plumb bob, or total station, for which multiple measurements of this density would be laborious at best. Such a section — a representation as visually explicit as it is precise — makes it possible to quantify, with a level of detail on the order of five millimeters, the vault-induced outward deformation of the building.
Analysis
Any such subset of the cloud data can be imported into computer-aided design software such as AutoCAD, for the iteration of potential proportional schemes, using the robust shape generation and mensuration tools proper to such programs.
