Kreon portable measuring arm in heritage preservation

The Bangkok Mahadthai Uthit Bridge (Thailand), more usually known as the Weeping Bridge, its sculptures and stucco, were recently part of an ambitious heritage preservation program using 3D scanning.

In order to completely inspect the details of sculptures and stuccos, to anticipate the potential needs of duplication and to save the whole heritage, a big part of the bridge has been scanned in 3D. Heritage experts chose not to use molding (the traditional reproduction process) but non-contact scanning to acquire data without deteriorating the surfaces of the bridge.

Three different solutions were confronted in real conditions: white light 3D scanner, handheld 3D scanner and scanning arm. Kreon’s solution (measuring arm and 3D scanner), proposed by its official partner in Thailand, GeoWorks, was selected after testing due to its ease of use, fastness, reliability and large measuring volume. Unlike white light 3D scanner, a scanning arm is able to scan large surfaces without having shadows. Unlike handheld 3D scanner, a scanning arm is able to locate itself in space.

A 3D laser scanner Zephyr II, integrated with a 7 axis 3,5 m Ace measuring arm, put on a telescopic tripod, were used for this study.

The arm is temperature regulated so as it runs outside and keeps measurement accuracy regardless of temperature or humidity conditions.

Due to the telescopic tripod and its mobility, the process was achieved in record time. The device succeeded scanning 20 meters of the bridge and height starting from 1 m (bas-relief) to 2,50 m (pillars) in a single evening.

Zephyr II high speed scanning (250 000 points /s) and wide laser line (100 mm) also provided process fastness. Zephyr II keeps a 15 µ accuracy independent from ambient light, and its resolution ensures a high level of precision for every sculpture restitution.

Performed for heritage purposes, this study was useful for artistic purposes, used to reproduce and carve stuccos and pillars in polystyrene.