Heritage Documentation at Hue Imperial Citadel: 3D Laser Scanning at Ngọ Môn

Documenting a historic monument accurately is the first step of any conservation project. It is also one of the hardest, because the structure itself cannot be touched, moved or subjected to destructive measurement. This case study describes how VMT Solutions surveyed Ngọ Môn, the principal gate of the Hue Imperial Citadel in Vietnam, using 3D laser scanning, drone photogrammetry and photography, and what that approach delivered for the conservation team.

Project overview

The challenge: documenting a monument that cannot be touched

Ngọ Môn is the main southern gate of the Hue Imperial Citadel, part of the UNESCO-listed Complex of Hue Monuments. Like most heritage structures of its age and status, its current condition has to be recorded precisely before any conservation or restoration work can be scoped, but the survey itself must be entirely non-invasive: no physical measurement on the fabric, no fixings, no contact that could affect the original substance.

The gate also combines fine architectural detail at ground level with a large tiled roof structure and upper pavilions that are difficult to reach and to measure from the ground. A single capture method would leave gaps.

The approach: terrestrial scanning, drone and photography combined

VMT Solutions surveyed Ngọ Môn with a combination of three techniques, each chosen for what it captures best:

• Terrestrial 3D laser scanning for the accessible facades, openings, columns and decorative stonework at and near ground level
• Drone photogrammetry for the roof structure, ridge details and upper pavilions that cannot be reached or measured safely from the ground
• High-resolution photography for colour, surface condition and material documentation across the whole structure

The work was carried out by the VMTS team of survey engineers and heritage-survey specialists. None of the methods requires physical contact with the monument, so the entire condition record was produced without touching the original fabric.

A second project in the citadel: Kiến Trung Palace

VMT Solutions has since carried out further scanning inside the citadel complex, including a laser-scanning survey of Kiến Trung Palace ahead of Festival Huế 2024. For that project the client needed a high-accuracy point cloud and mesh model of the palace facade as the basis for a 3D projection-mapping light show. The on-site survey was completed in a single day and the data processed within two days, so the design team could start work on schedule.

The same survey data that supports a projection-mapping design can also serve conservation documentation, virtual tours and, where a project calls for it, a BIM model. The capture is done once; the deliverables follow the use case.

The result

The Ngọ Môn survey produced a detailed, accurate record of the gate’s current condition, giving the conservation team a dependable geometric reference for restoration planning, with no physical contact with the heritage structure at any point. Combined with the later work on Kiến Trung Palace, it is part of a growing VMTS record of 3D documentation inside one of Vietnam’s most significant heritage sites.

VMTS heritage documentation: Vietnam and beyond

Heritage documentation is a long-standing part of the VMTS portfolio. Alongside the projects in Hue, VMTS has surveyed and modelled heritage buildings in Europe, including Schloss Laufen in Switzerland, the Staatsbibliothek zu Berlin in Germany, the Ronchamp Chapel by Le Corbusier in France, and the Elders Wool Stores heritage complex in Australia. Where a project requires a native BIM model of a historic building rather than survey documentation alone, that is delivered in Archicad, Revit or Allplan; see our overview of scan-to-BIM for heritage buildings and our guide to Point Cloud to Archicad for historic buildings.

Frequently asked questions