Notre-Dame de Bonsecours Church
Client / Collaborator
Municipality of Montebello
Sector
Architecture, Patrimoine, Religieux, Culturel
Location
Montebello
Services
Relevé LiDAR, Relevé par drone, Photogrammetrie, Visite Virtuelle
Mandate
As part of a digital preservation initiative for built heritage, DGTL conducted a complete 3D scan of the Notre-Dame-de-Bonsecours Church in Montebello, including the interior spaces, facades, roof, and hard-to-reach areas.
The goal was to create a comprehensive, quantifiable, and durable digital archive of the building’s current condition, capable of serving as a common reference for future restoration, maintenance, and conservation work. The survey was intended to document not only the church’s overall geometry but also its architectural details, masonry, and heritage elements, so that various professionals and craftsmen could observe, measure, analyze, and plan their work based on a single representation of the existing structure.
Mandate
As part of a digital preservation initiative for built heritage, DGTL conducted a complete 3D scan of the Notre-Dame-de-Bonsecours Church in Montebello, including the interior spaces, facades, roof, and hard-to-reach areas.
The goal was to create a comprehensive, quantifiable, and durable digital archive of the building’s current condition, capable of serving as a common reference for future restoration, maintenance, and conservation work. The survey was intended to document not only the church’s overall geometry but also its architectural details, masonry, and heritage elements, so that various professionals and craftsmen could observe, measure, analyze, and plan their work based on a single representation of the existing structure.
Proposition
A case study from our annual pro bono initiative
As part of its annual pro bono initiative, DGTL used the digitization of the Notre-Dame-de-Bonsecours Church as a case study to compare different 3D capture approaches under real-world conditions. The goal was to evaluate not only the speed and density of the data produced, but above all its completeness, precision, accuracy, and ability to be validated transparently..
A single control network as a reference
A high-precision primary control network was first established and georeferenced to create a common geometric basis for the entire project. This allowed all technologies to be tied to the same reference frame and then compared directly with one another without positioning differences skewing the analysis. The resulting network has a positional accuracy of less than 3 mm over typical distances of 100 m.
A Comparison of Three Digitization Approaches
The building was then documented using mobile LiDAR, terrestrial LiDAR, and a hybrid approach combining several complementary technologies, including drone-based photogrammetry. This approach combines the geometric accuracy of LiDAR, the speed of mobile scanning, and the very high level of visual detail provided by photogrammetry.
All of the datasets were ultimately compared, verified, and integrated to produce a representation of the building that was as comprehensive, precise, accurate, and verifiable as possible. This methodology also makes it possible to transparently document the strengths and limitations of each technology, rather than treating 3D scanning as a one-size-fits-all method.
Deliverables
High-precision point clouds
Several point clouds were generated using different capture technologies and then tied to the same control network to enable their comparison and integration. The terrestrial LiDAR survey achieved an average assembly error of 1.0 mm indoors and 2.3 mm outdoors, with an average error of 0.9 mm when attached to the control network. The mobile LiDAR survey, meanwhile, had an average assembly error of 2.2 mm.
Point Clouds and Photogrammetric Data
Drone imagery was used to complete the facades, the roof, and hard-to-reach areas. More than 6,000 georeferenced images were acquired and tied to the control network. The photogrammetric point cloud has an overall accuracy of between 3 and 5 mm, with an error of 3 mm measured at the control points.
High-resolution orthophotos
High-resolution orthophotos of facades and exterior elements allow for direct observation of materials, joints, cracks, and architectural details. The imagery achieves a ground resolution of approximately 1.16 mm per pixel, providing visual documentation detailed enough to support inspection, restoration, and the planning of interventions.
Textured 3D mesh
Using thousands of images captured by drone, a high-resolution textured 3D mesh was generated to combine the building’s geometry with a detailed photographic representation of its materials and heritage features. It provides an intuitive view of the building while allowing users to virtually examine areas that are difficult or dangerous to access..
Quality Report
A detailed quality report accompanies the data to document the methodologies used, the control network, the assembly parameters, and the precision and accuracy statistics specific to each technology. This documentation provides insight into how the data was generated, allows for an objective comparison of the different methods, and demonstrates the geometric reliability of the deliverables.
Virtual Tour
A virtual tour also complements the building’s documentation and provides professionals with remote access to the digitized spaces. It serves as a visual supplement to the metric data and makes it easier to explore the building when contextual information is needed. The virtual tour is, in fact, already listed as one of the services associated with this project on the DGTL page.
X-RAY STYLE PLANS
These drawings are quick to create and scale, so they can be imported into Revit or AutoCAD for drafting purposes.
COMPARING TECHNOLOGIES
As part of this project, three digitization approaches were compared : Mobile LiDAR scanning, terrestrial LiDAR scanning, and a hybrid approach combining terrestrial LiDAR and drone-based photogrammetry.
Each method has its own strengths in terms of speed, accuracy, density, and coverage. In the hybrid approach, the terrestrial LiDAR survey, tied to the high-precision control network, serves as the geometric reference base.
The photogrammetric data collected by drone is then integrated into the model to complete the facades, roofs, and areas that are difficult to see from the ground.
The result is therefore not simply a superimposition of multiple surveys, but a single, coherent, and continuous dataset that combines the geometric accuracy of LiDAR with the coverage and level of detail provided by photogrammetry..
The bell tower highlights the limitations of surveys conducted solely from the ground: certain elevated, recessed, or obscured areas remain difficult to access or invisible. DGTL’s True Hybrid approach combines ground-based LiDAR, used as a geometric foundation alongside the control network, with drone-based photogrammetry to fill in these areas and produce a single, continuous, accurate, and comprehensive survey.
Détail capturé avec une technologie LiDAR dynamique Détail capturé avec une technologie LiDAR terrestre Détail capturé avec l'approche « True Hybrid » de DGTL.
Skylights and their wooden louvers illustrate the importance of having a visual view of high-up components, which are often impossible to inspect from the ground. DGTL’s True Hybrid approach allows for a close-up examination of the condition of the slats, joints, and finishes, while precisely integrating them into the roof’s overall geometry.
Lucarne capturée à l'aide de la technologie LiDAR dynamique. Lucarne capturée à l'aide de la technologie LiDAR terrestre. Lucarne capturée avec l''approche « True Hybrid » de DGTL.
The details of the windows and facade bands reveal another significant limitation of surveys conducted from the ground: their upper surfaces remain virtually invisible. DGTL’s True Hybrid approach makes it possible to document these overhanging areas, capture the complete geometry of the frames, and assess the condition of horizontal surfaces—where water, debris, and deterioration can accumulate.
Détail d'une fenêtre capturé avec la technologie LiDAR dynamique. Détail d'une fenêtre capturé avec la technologie LiDAR terrestre. Détail d'une fenêtre capturé avec l'approche « True Hybrid » de DGTL.
DGTL's True Hybrid approach provides a clear view of the masonry layout and mortar joints, even on upper floors that are difficult to observe from the ground. It also reveals the details of the connections between the window arches and the facing, providing much more precise documentation of the joints and their condition.
Détail du mur du deuxième étage capturé à l'aide de la technologie LiDAR dynamique. Détail du mur du deuxième étage capturé à l'aide de la technologie LiDAR terrestre. Détail du mur du deuxième étage capturé avec l'approche « True Hybrid » de DGTL.
Masonry that protrudes significantly creates areas of occlusion for terrestrial LiDAR: from the ground, the upper surfaces of certain stones remain invisible, resulting in gaps in the point cloud. DGTL’s True Hybrid approach fills in these areas using aerial viewpoints, making it possible to reconstruct the complete geometry of the stones, joints, and relief surfaces.
Couverture partielle de la maçonnerie lors de l'utilisation de la technologie de numérisation LiDAR Couverture partielle de la maçonnerie lors de l'utilisation de la technologie de numérisation LiDAR Couverture complète de la maçonnerie grâce à l'approche « True Hybrid » de DGTL.
This comparison simply illustrates the difference in level of detail achieved depending on the technology used. As we move from mobile LiDAR to ground-based LiDAR, and then to DGTL’s True Hybrid approach, the geometry of the stone and the joints becomes progressively more defined, continuous, and true to reality.
Niveau de détail de près avec la technologie de numérisation LiDAR mobile. Niveau de détail de près avec la technologie de numérisation LiDAR terrestre.. Niveau de détail de près avec l'approche « True Hybrid » de DGTL.
Virtual Visit
Explore the Notre-Dame-de-Bonsecours Church through a comprehensive virtual tour—both interior and exterior—that allows you to virtually revisit the building, examine its architectural details, and take approximate measurements. This digital archive serves as a reference tool for coordinating, preserving, and monitoring the building’s condition over time.