Saint-Laurent Catholic Church, Montreal
Client / Collaborator
Nadeau Blondin Lortie Architectes
Sector
Architecture, Patrimoine
Location
Montreal
Services
Relevé LiDAR, Relevé par drone, Photogrammetrie
Mandate
As part of ongoing renovation work, the right bell tower of Saint-Laurent Catholic Church is currently partially inaccessible due to scaffolding. The architecture team needed complete documentation of the left bell tower to use as a mirror reference to guide decisions, validate geometry, and support planning for work on the right bell tower.
The objective was simple yet demanding: to see, document, measure, and be able to draw each stone. This required very high-density 3D scanning, high accuracy, and complete coverage of architectural details in order to produce reliable data for drawing, coordination, and monitoring the condition of the materials.
Mandate
As part of ongoing renovation work, the right bell tower of Saint-Laurent Catholic Church is currently partially inaccessible due to scaffolding. The architecture team needed complete documentation of the left bell tower to use as a mirror reference to guide decisions, validate geometry, and support planning for work on the right bell tower.
The objective was simple yet demanding: to see, document, measure, and be able to draw each stone. This required very high-density 3D scanning, high accuracy, and complete coverage of architectural details in order to produce reliable data for drawing, coordination, and monitoring the condition of the materials.
Proposition
In order to obtain a defensible geometric basis and coverage without missing areas, we proposed a hybrid methodology combining a network of control points, high-precision LiDAR surveying, and a very high-resolution drone photogrammetry mission.
Network of control points at the total station
Establishment of a network of control points measured at the total station to structure the project, ensure metric stability, and guarantee the alignment of data sets.
LiDAR scanning
The LiDAR survey provided the geometric basis for the project, establishing the exact scale, shape, and spatial context. It served as a reliable geometric reference, the scale and truth of the project.
Photogrammetry
A planned drone mission was carried out to capture the entire left bell tower from multiple angles, with dense coverage of cornices, moldings, supports, and decorative elements. The images were linked to the primary network to produce a detailed, consistent, and usable 3D reconstruction.
In total, approximately 3,600 images were produced and aligned with the LiDAR point cloud, combining the accuracy of the survey with the level of detail provided by close-up shots.
Deliverables
The final deliverable combines the best of both datasets to produce a single, comprehensive, and usable database for design and analysis.
High-density, high-precision, high-accuracy color point cloud
Delivery of a very high-density color point cloud, derived mainly from photogrammetric processing and constrained by the control network and LiDAR reference to ensure reliable geometry. This format is particularly effective for 3D documentation of heritage buildings in Montreal and Quebec.
Facade orthophotos at 1 mm per pixel
Facade orthophotos at 1 mm per pixel accompany the survey and allow for clear visualization of cracks, defects, joints, and stone details.
3 mm per pixel “X-Ray” orthogonal images
Generation of 3 mm per pixel black and white orthogonal images, designed to speed up the production of elevations in AutoCAD and Revit. These images can be placed to scale, serving as a quick basis for tracing, checking alignments, and documenting geometries.
This hybrid methodology provides 3D documentation that is particularly well suited to heritage buildings and facade restoration projects in Montreal and Quebec. It offers a precise working medium for inventory, measurement, drawing preparation, and monitoring the condition of materials.
