PAST, PRESENT & FUTURE: Using Digital Technologies to Support Conservation (photogrammetry vs. laser scanning) Dr Eujin Pei and Anthony Eland School of Design, De Montfort University Introduction Project aims: To demonstrate the use and application of relevant digital techniques (photogrammetry vs. laser scanning) for local and national heritage groups concerned with buildings and their artefacts 1
The geophysics team at English Heritage recently hired a JCB utility vehicle to help undertake a detailed survey of the ground surrounding Stonehenge. This ground penetrating radar (GPR) analysis has resulted in highly accurate 3D mapping of the fine detail of objects down to a depth of 2m. http://www.executivehirenews.co.uk/latest news/2010/12/17/jcb aids stonehenge survey/ Makerbot Fused Deposition Machine via Additive Manufacture http://store.makerbot.com/replicator 404.html 2
Full colour 3D printing via Zcorp Z Printer 450 Material loading, set up and powder extraction are all handled by the machine within its confines. http://www.zcorp.com/en/products/3d Printers/138/spage.aspx 3
Detailed metric laser survey for part of the UNESCO world heritage site at Durham Cathedral using a Faro Photon120 phased based laser scanner. All the scans were carried out a very high point density and colour photography was also taken at each scanner setup. http://www.digitalsurveys.co.uk/durham cathedral metric survey/ 4
The application of such technologies can be generally classed as: Scanning devices (such as surveying and recording of historic buildings and structures, etc.) Modelling systems (such as 3D digital modelling, printing of scaled models of buildings and artefacts, etc.) Visualisation i techniques (such as Augmented Reality (AR), Virtual Reality (VR), interactive and animated displays, and mobile and locative systems, etc.) Object Based Conservation : The study and preservation of ancient artefacts Location Based Heritage : The study and dissemination of information concerning ancient monuments and buildings For thispresentation, i we will look at object based b conservation. 5
Object Based Scanning Techniques : 1. Contact Scanning (Probe scan) 2. Optical Scanning (Photogrammetry) 3. Laser Scanning (Infra red scan) Object based Case Study Solid plaster cast replica of a statue of a cat utilising Photogrammetry Anglo Saxon object made from crystal utilising Laser Scanning 6
Contact Scanning Scanning probes provide a continuous deflection output combined with the machine position to derive the location of the surface. The probe stylus tip is brought into contact with the feature and then moved along the surface, gathering data as it moves. http://www.laserdesign.com/products/scanners_and_software/portable_laser_scanners/surveyor_fa series/ http://www.renishaw.com/en/scanning probes 6656 Optical Scanning Photogrammetry systems employ triangulation, whereby intersecting lines in space compute the location of points and surfaces in all three dimensions and where objects are measured without being touched. http://www.imetric.com/index.php?id=30 7
Laser Scanning A laser dot or line is projected onto an object and a sensor measures the distance to the surface. Data is collected in relation to an internal coordinate system to map the surface geometry. http://www.imetric.com/index.php?id=30 1. Optical Scanning via Photogrammetry 8
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2. Infra red Laser Scanning 12
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Discussion Photogrammetry vs. Laser Scanning 14
Photogrammetry 1. Indoor / outdoor lighting can give different results depending on the weather. Solution: Take photos in a more controlled environment. 2. Singular colours and fine textures (e.g. such as hair) are difficult to triangulate. Solution: Use colour reference points 3. Having overlapping images can help achieve greater accuracy, but problematic to simultaneously computelarge number of images. 4. Choosing automatically produced geometry sometimes resulted in distorted models. Solution: Manually triangulating points through having several images. Laser scanning 1. Bottom of the surface not detected. Solution: Raise the object. 2. Issue of transparency and reflectivity of crystal. Solution: dust an inert coating of powder and increase the scan resolution. 3. Post processing was time consuming. Solution: requires greater familiarity with Materialise Magics software. 15
Next Steps: Immersive viewing / hologram / augmented reality / 3D stereographic displays, etc. Produce physical artefact via additive manufacture, etc. Conclusion Over view of emerging technologies Photogrammetry vs. Laser Scanning Visual output / physical object 16
School of Design, De Montfort University Anthony Eland: AEland@dmu.ac.uk Dr Eujin Pei: Epei@dmu.ac.uk 17