Documentation of objects has always been the foundation of material culture research and conservation. Replacing and amending traditional methods, 3D documentation is increasingly being used as it more fully captures the original nature of the object. Although it is possible to simply draw objects in 3D by hand in the same way as we would make drawings on paper, automated scanning techniques offer much more accuracy and precision. There are many different techniques used for capturing 3D data.1 For capturing objects of cultural value, none-invasive techniques are preferred. Three techniques are commonly used in archaeology and related fields today:
- Laser scanning
- Structured light scanning
- Image based modelling
Laser scanners measure distance by measuring the time a laser beam takes to get back to the scanning device.2 In 1960s this technique was developed to measure the distance to the moon.3 Today, airborne laser scanners are used to measure the surface of the earth in detail, while land based laser scanners can be used to scan objects of a range of sizes.
The main advantage over structured light scanners is that laser scanners are much faster in capturing large areas or objects such as building exteriors or interiors. Structured light scanners however are able to acquire higher precision.
Structured light scanners scan a surface by projecting a light pattern over an object. The pattern deforms on the surface of the object, which is registered by one or more cameras. Software is used to accurately calculate the 3D shape of an object based on these deformations.
Structured light scanners are able to reach great precision because they sample the same surface several times. A drawback is that fixed position structured light scanners are bound to the size of the projected pattern, making it impractical to scan large objects. More recent scanners allow more free movement and object size is less of a limitation. They also do not work well in strong exterior light conditions as the projected light might not contrast enough with the surroundings. Hence, structured light scanners are best suited to record small to mid-sized objects under controlled conditions inside.
Image based modeling4 is the technique of generating 3D models from a set of 2D images. A photocamera is used to capture a multitude of images from an object, which are fed into software that uses advanced image analysis algorithms to reconstruct camera position and distance. The technique can be used in combination with any kind of camera, even smart phones are effectively used today as 3D scanners. However, lense type, camera resolution and setup determine the quality of the final model.
As photocamera's are used as scanning device, the technique is very flexible and scalable. One popular application nowadays is capturing drone footage, allowing for fast scanning of large areas. This way we are able to document buildings, excavations, and landcapes.
Scanning facilities at the 4DRL
The 4D Research Lab has the facilities to document cultural objects such as art works, artefacts, and architecture. We can also scan archaeological excavations. We have two structured light 3D scanners at our disposal, and expertise in structure-from-motion or image based modelling with regular cameras and drones. Our techniques and approaches are selected based on your research questions and tailored to suit your desired end uses and outputs.
- See Wikipedia
- Some laser scanners work however with triangulation, in which case it must be teamed up with a camera. Yet others work with measuring phase differences between the outgoing and incoming beam
- In the Lunar Laser Ranging experiment: Wikipedia
- Also referred to as the related concepts Structure from motion or photogrammetry