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3D Digitizer Applications
Measuring Instruments
3D Digitizer Applications
Reshaping Colosseum
Reshaping Colosseum
Gaiani, Balzani,Uccelli
University of Ferrara, Polytechnic of Milan
The following editorial is an abstract from the journal article 'Reshaping the colosseum in Rome: an integrated capture and modelling method at heritage sites' by Gaiani, Balzani & Uccelli, Eurographics Association and Blackwell Publishers, Vol 19 (2000) No. 3 and was presented at the Eurographics 2000 Association Meeting in Interlaaken, Switzerland. Reprinted with kind permission of Blackwell Publishers, UK.
Reshaping the Colosseum in Rome (University of Ferrara, Polytechnic of Milan)
Abstract
This paper describes the process of building Internet-transmittable, 3-D digital virtual models of ancient heritage monuments from on-site data, focusing especially on 3-D dimensional acquisition techniques and colour processing methods.
Introduction
As a large ordered database of spatial information, a 3-D model can be added to and altered over time, provide a more accurate representation of the real life of the monuments than a 2D drawing and can also be a powerful tool for complementary analyses.
Recent improvements in digital technology in the fields of 3-D imaging, 3-D data capture and colour images, in addition to methods developed at Nub-lab University of Ferrara for combining 3-D vector files and colour images, can now reliably and accurately digitise the external shape and reflectance of parts, ornaments or whole architectural complexes. The resultant restitution as a 3-D digital photorealistic model is suitable for use as a working tool for restoration planning.
Survey of iconic column base, location north-west facade (size ca. 130x80x50 cm). Distance to object 100 cm, zoom step 4, resolution x,y=1.25 mm, res. X=0.61 mm. Field of view ca. 25x25 cm, total number of scans=38, each shot max. 10.000 3-D points. Accuracy <1mm
The Konica Minolta VIVID 700
A Konica Minolta VIVID 700 range camera using technology based on optical triangulation was adopted to survey architectural elements and the frieze. The Konica Minolta VIVID 700 is best suited for close range study of smaller objects (1x1x1m). The system is portable and designed to work in difficult environments, making it particularly suitable for architectural applications.
Survey of iconic capital base, location north-west facade (size ca. 130x80x50 cm). Distance to object 100 cm, zoom step 4, resolution x,y=1.25 mm, res. X=0.61 mm. Field of view ca. 25x25 cm, total number of scans=41, each shot max. 10.000 3-D points. Accuracy <1mm
Range Processing Pipeline
Given the sensors' limited field of view, complex environments might require a large number of views. Each 3-D sensor view provides an ordered set of 3-D points in a camera centered Cartesian coordinate system. Model reconstruction is obtained by systematic application of this Cartesian coordinate system to every view taken. This process is known as registration and aligns the scans.
The Konica Minolta VIVID 700 laser scanner allows multiple scan registration from the digital colour pictures saved with the range image using homologous points on pairs of views of the same subject. The intensity values measured by the range sensor are used to constrain the matching of sensors between views. The labeling of points is then used to identify common portions of surfaces between images to allow for registration. Finally the algorithm is applied globally to merge multiple scans into a single point cloud, without overlapping or discontinuities.
Colour Processing Pipeline (Texture mapping)
Proper geometric fit of the image from the photometric camera onto the 3-D geometric model is essential. We used commercial software from Alias|Wavefront Studio Version 9. to apply the orthographs from the digital images taken with a Konica Minolta RD175 camera and a Konica Minolta 800 si. as projection textures over the model like planar projection. The final visual results, even when several images are collated into a mosaic, are excellent, even by time consuming criteria.
Survey of decorative frieze. An engraved frieze, located in the hypogeum (size ca. 80x90x10 cm). Distance to object 100 cm, zoom step 4, resolution x,y=1.25 mm, res. X=0.61 mm. Field of view ca. 25x25 cm, total number of scans=34, each shot max. 10.000 3-D points. Accuracy <1 mm.
Conclusion
Emerging 3-D survey and measurement technologies, from close range scanners to large lidar systems in addition to new reflectance acquisition techniques, enable significantly faster, cheaper and more accurate documentation of monument conditions.
Equally important, emerging data collection technologies also allow the detailed, accurate digital archiving of current dimensional conditions for future generation and may help obviate the need for the many well-intentioned but inaccurate and destructive physical reconstruction and restoration taking place at heritage sites.
Marco Gaiani (Polytechnic of Milan), Marcello Balzani (University of Ferrara), Federico Uccelli (University of Ferrara)
