THE ROLE OF TECHNOLOGY IN THE RECONSTRUCTION OF NOTRE-DAME IN PARIS

由专筑网亚森君，王雪纯编译

巴黎圣母院在经历可怕的火灾之后，重建的问题随之而生。政府尚未制定重建方针，人们都在思考我们能利用何种技术来帮助重建这座历史悠久的法国首都纪念碑。根据圣母院劳工基金会主任Eric Fischer的说法，重建被大火摧毁的圣母院需要几年的时间。如果必须耐心等待，以下几种技术可以帮助建筑师和工程师师恢复这一哥特式建筑杰​​作。

After the terrible fire that affected the cathedral of Notre-Dame de Paris ten days ago, the question of reconstruction arises. If the roadmap has not yet been established by the government, we wonder how technologies could help rebuild this historic monument of the capital. According to the director of the Notre-Dame Labor Foundation, Eric Fischer, it will take several years to rebuild what was devastated by the flames. If it were necessary to be patient, several technologies could help builders and architects restore this masterpiece of Gothic architecture.



在考虑重建这件艺术品时，3D扫描工作可能会有很大的帮助，尤其是Andrew Tallon所做的工作。他曾在美国瓦萨大学担任艺术教授，并于2013年将整个大教堂进行了数字化拷贝。

“我想知道当时的建设者在想什么，了解这些建筑是如何建造的，以及了解它们结构的位置。”——Andrew Tallon para National Geographic, 2015

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



为了“透视”纪念碑的墙壁，Andrew Tallon使用了激光和球形相机，这可以创建一个超精确的3D地图。这张地图可以描绘出火灾前后大教堂的状态。人们还可以使用Iconem等公司提供的3D扫描，分析其损害，然后再试着修复大教堂。就其方式而言，Iconem使用无人机拍照，并通过摄影测量技术在太空中定位每一张照片。当然，重建工作不会用塑料重建箭头，也不会很快让其再次出现在巴黎的天空中。对于这些机密建筑来说，这是一项需要仔细修复的完整工作，但对于一些不可见或不那么重要的元素，3D打印是有用的。该技术之前已经在一些重建中用于修复一些受损严重的雕塑的复制品。

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.



点云是从激光测量中获得的第一个三维结果，并且形成了可用3D处理和观察结构的令人印象深刻的工具。这些图可以包含数十亿个点，并且可以实现高达1 mm的测量精度，超越了传统的测量调查方式。

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.



测量领域的专家使用高端激光扫描仪技术创造了点云，这项技术性能、准确性和快速性都大幅提升。该数据库创建的虚拟模型为专员们提供了建筑物的所有尺寸，包括线、面、体。还可以用点云制作视频。

激光测量的三个主要组成部分是数据采集，汇总和剖切。

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.



点云数据的采集

测量激光距离有两种主要方法：- a）计算激光脉冲发射、从表面反射和返回的飞行时间；- b)计算正弦编码光束经过行进、反射和返回后的相移。在典型的扫描仪中，激光束通过旋转镜在水平360度和垂直270度的范围内分布，并且以每秒接近一百万次测量的速率获取其自身与其可以看到的每个表面之间的距离。其测量结果就是所谓的点云。

扫描分辨率是一个关键因素。使用较低点密度扫描将花费较少的时间，但由于点数太少，建筑物的细节将无法透过数据重建。虽然单个云将提供大量信息，但它只是一个单一的点;为了产生足够密度的测量并最小面积的遮挡，必须移动扫描仪。

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.





汇总

一旦获得了所需的站点和必要的控制点，就必须对数据进行登记，也就是说，用计算机进行汇编。该软件进行一系列插值，以在具有最小误差的各种控制点或约束之间创建匹配。通常需要抑制某些约束。

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.



剖切

记录数据后，可以通过限制可见点来创建剖面、平面图和视图。它的颜色根据海拔的高低而变化。因为扫描仪生成的是点，而不是平面，所以所有的表面都是透明的。

同样，用这些方法制作的剖面可以比传统的钢卷尺、铅锤或全站仪等工具更清晰地显示建筑物的信息，对于传统测量工具，要取得这种密度的数据是非常费力的。这样的剖面——一种视觉上清晰而又精确的表现形式——使得用5毫米级量化拱顶引起的建筑向外变形成为可能。

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.



分析

可以将任何这样的云数据子集导入计算机辅助设计软件（例如AutoCAD）中，使用适合于此类程序的形状生成器和测量工具来迭代潜在的比例方案。

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.