Survey of façades and sections: south transept of the Basilica of St Denis

Context

The Basilica of St Denis is recognised as the earliest masterpiece of monumental Gothic art. It is imprinted in the genes of the city of St Denis which developed around it. A classified historic monument, it is one of the leading heritage sites of the Paris region.

The problem

Inspection of the rose window of the south transept revealed significant deformation. For the regional organisation responsible for heritage matters, the DRAC Ile-de-France, it was important to act fast. A conservation and renovation programme was set up for the south transept as a whole. Numerous surveys were required before work could begin.

The project setting

• Historic monument
• Restoration of the rose window of the south transept
• 4400 m2 of façade to survey and plot

Objectives

• Survey of existing situation
• Base on which the architect in charge (ACMH) can plan the work

Requirements

• 4 sectional elevations (including detail beyond the section) at 1:50 scale
• 1 topographic plan
• 3 cross sections (without background detail)
• Plots including the detail of every stone
• Deformation analysis for the rose window

Constraints

• Limited clearance in which to work in front of most of the façades
• Building open to the public during the work

Our response

The deformation analysis was performed using a point cloud of the rose window. The high density of data captured (one point every 5 mm) enabled us to map the departures from the correct plane of the window extremely graphically. Thanks to this method of portrayal, we rapidly identified the sources of the various distortions present

This analysis was carried out using our own CloudSurfer software.

For the production of the plots we used a method combining laser scanning and photogrammetry:

• The geometry of the elevations and sections was extracted mainly from point clouds using AutoCAD and CloudWorx.
• The finer details including the stonework were plotted on orthophotos computed using our own ImgSurveyor software.

Deliverables

• 8 sections and elevations in .dwg and .pdf formats.
• 1 deformation analysis for the south transept rose window in .dwg and .pdf formats.
• Plots in .dwg and .pdf formats.