3D Scanning

Different machines and methods exist to 3D scan objects. You might not know it, but there are different ways possible to create a digital version of a real object. There are a lot of different 3D scanning methods, but today, we will focus on three of them, that we can consider as the main ones: Laser 3D scanning, photogrammetry, and structured light scanning. The choice of the 3D scanning technique will be made regarding your project or its context.

 

Laser 3D scanning

Laser 3D scanning is certainly the most common and used 3D scanning technique. Digitally capturing the shape of the object using laser light to get a digital representation of the real object. These 3D scanners are able to measure really fine details and capture free-form shapes to generate highly accurate point clouds.

 

This laser scanning technique is perfect for measurement and inspection of complex geometries. It allows getting measurements and data from where it is impractical with traditional methods!

A scanner using laser light is a little bit like a camera: it can only capture what is in its field of view. With this process, a laser dot or line is projected on an object from the device and a sensor measures the distance to the surface of this object.

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By processing this data, it can be converted into a triangulated mesh, and then a CAD model.

 

Structured Light Scanning

With this Structured Light Scanning method, one of the camera positions used in previous scanning methods is actually replaced by a projector that projects different light patterns on the surface of an object. The way the objects distorts these patterns is recorded, allowing to create the 3D scan.

The structured light scanning process is used in facial or environment recognition technologies.

 

How to use 3D scanning?

3D scanning can be a faster and easier technique to create a 3D model for 3D printing if you just want to recreate an existing object. Once you have your 3D model, you can add the modifications to it, it can actually be a great basis to start your project.  

 

What are the applications of these 3D scans? The medical sector is really making the most of this scanning technology. It is also helping to create made to measure prosthesis for patients, from 3D scans. The use of 3D scans is already quite popular in the dental sector, for example, to observe, simulate options, or even create some dental devices, like braces, implants, and dentures. Using 3D scanning and 3D printing is perfect to avoid all the disadvantages of molds and the whole process of creating these molds.

Using 3D Scanners In Archaeology
In English-speaking areas laser scanners are used in the field of preservation of cultural heritage and archaeology in an almost standardized manner. Well-structured recommendations offer an accurate guide both to the customer and business sides. The case studies and analyses on this subject appear in almost unfathomable amounts. We attempt to concisely review, what the SziMe3D project has achieved by now in order to provide the experts with an impression on the potentials of the technologies that are already available in this country, too.

 

This technology offers advantages:

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• The detailed survey is conducted without direct contact, at a distance with equal or better results than those by direct physical measurement, and no damage is done to the measured object;

• Scanning is particularly suitable for surveying objects with irregular surfaces, such as carved stones, built structures, archaeological features, and they are easy to be identified in the scanned data;

• Surveying is possible even under poor visibility and low illumination;

• The data are available and can be analysed by the experts in an unchanged but scalable and searchable form at any time;

• 3D models or even complete reconstructions may be created, which can be walked around, rotated and measured in the virtual space. 

 

Terrestrial laser scanners are suitable to documenting archaeological sites and features, ruins as a whole,while the structured light scanners are fit to create models of smaller objects, artefacts with replica level details.

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Scanning of buildings, archaeological features

The top-of-art terrestrial laser scanners can scan up to 1 million points in a single second. In practice this capacity is only worth using when surveying the details, because the resulting file’s size will be extraordinary large. The density of the recorded points, their measured distance from each other, can vary depending on the task. In our experience we found that for surveying archaeological features the optimal setting is the one, when the points are 3 millimetres away from each other at the distance of 10 meters measured from the scanner in the point cloud generated by the scanner. In this case the optimal distance of the object is about 20 m (the scanner we used had a range of 0.3 m to 187 m). If higher quality is required, it is possible to set the resolution up to 0.6 mm measured also at 10 m from the scanner. However, in such cases it has to be considered that measurement time leaps to hours, the recorded file’s size increases drastically, almost to uncontrollable measure.

 

In most cases the camera built in the scanner does not provide images with sufficient quality and resolution, therefore to create correctly coloured textures we have to take photographs with high quality photographic camera and lens placed exactly matching with the scanner’s position. The coupling of terrestrial laser scanner survey data with the National Unified Projection system (EOV) is solved using a GNSS (Global Navigation Satellite System) receiver. The terrestrial laser scanner we use employs a Class I laser unit that does not pose a threat to human health.

 

Scanning of objects, archaeological artefacts 

We usually use devices implementing structured light to survey objects in 3D. These devices are able to scan the items with several tens of microns resolution and with the precision of the one third-quarter of the resolution value. The proper selection of the task-dependent work space (i.e. deciding how big area we can survey at the same time) can be completed with the replacement of lens system.

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Surveying and processing procedure

It is evident that the terrestrial and object scanners are able to survey only what they ‘see’. When selecting the appropriate number and location of the measuring positions we do as if we surveyed the measured features with our own eyes. We are searching for point of view from where every detail, every obscured surface is visible. Careful design of the measurement may seem a lengthy procedure but can prove itself to be quite rewarding in the processing phase.

 

Any thorough the planning and execution can be, it is impossible to avoid having non-surveyed areas. These ‘holes’ can be completed then with processing program assisted solutions, tailored to the environment and the available photo shots, and, in most cases, in satisfactory manner. We use target points for terrestrial scanners to join the files recorded from different measuring positions. Previously it was necessary to use such targets for the object scanners as well. The state of the art, colour object scanners we use are able to search themselves reference points based on the shape and texture of the objects and combine the scanned data on their basis. Although surveying from one measurement position may take only a few tens of minutes, the survey of a several hundred square meters large excavation area definitely requires a full day. However, it still takes a lot less time than surveying the excavation with the traditional methods and owing to the fixation of control points for measuring with a total station. Data processing takes twenty times longer than surveying. We can calculate the same way in case of objects as well.
 

The Yields of the work

It is important that before doing the survey, archaeologists and survey processing technology experts together determine the goals and scope of the survey, the expected point density and accuracy, the features, tolerances of the drawings to be produced, the requirements for the photographs, the forms of displaying, publishing, the format of the data to be transferred and the deliverables. Today, in the ‘learning phase’, when the frameworks of these requirements are just taking shape, for the time being we are not quite exactly working that way as described. We generate a data file with maximum accuracy including every possible detail, and from that file we can produce virtually anything the experts of various fields may want.

 

Clarifying the purpose and intended audience of the survey is essential. Scientific documentation, cultural and educational presentation or publication on the web all demand entirely different solutions. The snapshot-like recording of the exact status of an archaeological feature or as detailed as possible 3D presentation of an object require surveying with the best measurement parameters. The resulting files that way are manageable only by the latest and fastest computers, with dedicated software. On the contrary, displaying in the web requires sufficiently small-sized, ‘dumbed-down’ files. It is impossible to equally well serve the two extremes with the same tools. Nowadays we have to resign ourselves to the fact that the hardware used in the survey is a major step ahead of the software available for processing and visualization.

 

Many people fear that the electronically recorded data may be lost, and because of the frequently-changing data formats, over time they will not be possible to read. The lack of standards, the countless formats used by the manufacturers is also a problem. Nevertheless, there are basic formats, which are not affected by the passage of time, and will be able to be processed at any time (e.g. the ASCII). Besides the possibilities presented so far there are innumerable other applications worthy of mention, which are available only owing to 3D laser technology. From among them, we would single out the 3D printing, with which close to reality replicas of the artefacts can be produced, and thus they can even be ‘taken home’ with us.

 

Based on international experience now we can confidently state that the technology we have presented hereby greatly contributes to the accurate documenting, better presentation and generating interest towards our cultural values. However the more accurate and detailed documentation than ever before may not serve as an excuse to dismantle, destroy our cultural values, it is rather a new instrument to preserve and save them.