TECNICHE DI RILIEVO E MODELLAZIONE 3D applicate ai Beni Culturali

TECNICHE DI RILIEVO E MODELLAZIONE 3D applicate ai Beni Culturali Fabio REMONDINO 3D Optical Metrology (3DOM) Bruno Kessler Foundation (FBK), Trento, Italy Email: remondino@fbk.eu http://3dom.fbk.eu

3D Surveying and Modeling Surveying: reality-based / metric recording of 3D data (point clouds) of existing structures real measurements on the field (photogrammetry, laser scanning, etc.) Modeling: generation of structured 3D data (mesh, TIN) from unstructured surveyed data 3D Modeling is a chain of lossy procedures and data transformations performed to derive new products 3D SURVEYING & MODELING Data collection Data processing 3D product visualization, analysis, interpretation, etc.

Traditional (3D) recording method E.g. Hand recording Tape measurement Close contact Small areas Subjective Allows detailed understanding May be attached to other forms of survey Time consuming Geomatics 3D recording methods (reality-based) Modern geomatics techniques are digital, objective, rapid, three-dimensional and cost effective Techniques rely on harnessing the electromagnetic spectrum Active (range) Passive (image)

Reality-based modeling Techniques for 3D Data Recording Image-based techniques (passive sensors) - photogrammetry, computer vision, shape from X, etc. dense or sparse 3D points (point cloud) Range-based techniques (optical active sensors) - laser scanners, stripe projection systems, radar, etc. TOF or triangulation measurement principle dense point clouds Surveying methods - GNSS, Total stations, maps, etc. sparse points, low density, low resolution model, time consuming Procedural modeling Computer graphics (3DStudioMax, Maya, Sketch-up, etc.) - no real measurements 4

Object / Scene Complexity [points/object] Techniques for 3D Data Recording 10 Mil Close-range 1 Mil 100 000 Satellite Aerial photogrammetry photogrammetry and terrestrial laser scanners Remote Sensing and LiDAR 10 000 1 000 100 GNSS Hand 10 1 Total stations Tactile / CMM measurements 0.1 m 1m 10 m 100 m 1 km Object / Scene Size 10 km 100 km 1000 km after (Boehler, 2001)

Reality-based techniques Photogrammetry Image-based techniques (passive sensors) Photogrammetry, computer vision, shape from X, etc. Satellite, aerial, UAV or terrestrial platforms Linear array or frame CCD / CMOS sensors Different geometric, radiometric and temporal (archives) resolutions Manual or automated measurements Dense or sparse point clouds Quite cheap technique but experience required Need of stereos and a mathematical model to derive 3D data

PHOTOGRAMMETRIC PRINCIPLE how does it work? - 2D images need a mathematical model to terrestrial example convert the image measurements into 3D data - At least 2 images to derive 3D information object - Collinearity principle - Camera calibration to correct systematic errors due to lens distortion Z Y X Reference system OA OB image A image B 7 7

EXAMPLE OF PHOTOGRAMMETRIC WORK 3D Reconstruction of the Big Buddha in Bamiyan, Afghanistan Before March 2001: - 53 m high - tallest representation of a standing Buddha - niche full of frescos After March 2001: - empty niche - no more frescos - risk of collapse 8

EXAMPLE OF PHOTOGRAMMETRIC WORK 3D Reconstruction of the Big Buddha in Bamiyan, Afghanistan 3D Modeling: Internet, Tourist and Metric images 9

EXAMPLE OF PHOTOGRAMMETRIC WORK 3D Reconstruction of archaeological areas and excavation artefacts

EXAMPLE OF PHOTOGRAMMETRIC WORK 3D Reconstruction of statues, bass-relief, small monuments

EXAMPLE OF PHOTOGRAMMETRIC WORK 3D surveying of the Façade / Portal of Saint-Trophime, Arles (France), ca 1250 Ca 12 m width and 20 m height 90 images Canon EOS 5D Mark II (21 megapixels) 24-85 mm lenses ½ day in the field, 3 days of processing 12

EXAMPLE OF PHOTOGRAMMETRIC WORK Façade / Portal of Saint-Trophime, Arles (France) POINT CLOUDs 45 mil pts 13

EXAMPLE OF PHOTOGRAMMETRIC WORK Façade / Portal of Saint-Trophime, Arles (France) POINT CLOUDs 14

EXAMPLE OF PHOTOGRAMMETRIC WORK Façade / Portal of Saint-Trophime, Arles (France) ORTHOIMAGEs 15

EXAMPLE OF PHOTOGRAMMETRIC WORK Paestum, Cerere Temple (ca 100 x 60 x 15 m), 250 images 16

Reality-based techniques Techniques for Data Capturing 3D Scanning Range-based techniques (active sensors) Laser scanning, structured light systems, radar, etc Aerial (LiDAR) or terrestrial range sensors Triangulation vs time-delay measurement principle Expensive and bulky sensors with no or low-res texture information Multiple returns or full waveform Each sensor is range-dependent & almost weather- and light-independent Provide directly 3D information in form of dense point clouds Fast acquisitions of the geometry & easy to use Lack of good texture information Long processing time

EXAMPLE OF LASER SCANNING WORK Vasari s Adorazione dei Magi (ca 1550) 84 scans @ 0.3 mm - ca 200 Mil. points 2.6 x 2 m Conservation reasons & study of paint detachment, 60 Mil polygons model textured 18

EXAMPLE OF LASER SCANNING WORK Tre Cime / Three Pick / Drei Zinnen, Lavaredo, Dolomiti UNESCO

EXAMPLE OF LASER SCANNING WORK

Techniques for Data Capturing Integration No panacea: techniques used in combination / integrated mode generate best results [Guidi, G., Remondino, F., Russo, M., Menna, F., Rizzi, A., Ercoli, S., 2009: A Multi-Resolution methodology for the 3D modeling of large and complex archaeological areas. International Journal of Architectural Computing, Vol. 7(1), pp. 39-55] [Remondino, F., El-Hakim, S., Girardi, S., Rizzi, A., Benedetti, S., Gonzo, L., 2009: 3D Virtual reconstruction and visualization of complex architectures - The 3D-ARCH project. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. 38(5/W1), Trento, Italy]

3D MODELING: IMAGE- VS RANGE-BASED Photogrammetry = passive method (passive sensors) = image-based method Laser scanner = active method (active sensors) = range-based method Image data acquisition Range data acquisition (3D point cloud) Image pre-processing Calibration and orientation Editing and alignment Measurements and & 3D point cloud generation Surface generation and Texture Mapping Surface generation and Texture Mapping Visualization, GIS products, replicas, inspection, virtual restoration, etc. Visualization, GIS products, replicas, inspection, virtual restoration, etc. 1:6 1:8

3D MODELING: and then?? Original object 3D model Segmentation results Segmentation for object classification, analyses, online access, etc. 23

3D MODELING: and then?? IR and UV mapping to retrieve metric information

3D MODELING: and then?? Ascent route in 3D Physical replicas 25

3D MODELING: and then?? 3D GIS in order to access to 3D geometric data linked to external information GE & ESRI

3D MODELING: and then?? Calcolo delle dispersioni termiche Tetto 25%-30% Serramenti 20%-25% Pavimenti 15%-20% Qualitativa Confronto di zone a differente dispersione termica attaverso un ispezione visiva Semi-quantitativa Calcolo delle zone isoterme all interno di una superficie unitaria Quantitativa Calcolo di dispersione termica sulla superficie attraversico una metrica 27

Conclusions Rilievo e modellazione 3D di beni culturali a scala diversa Fotogrammetria (immagini) e laser scanner Stessi risultati in termini geometrici Approcci tradizionali sono ormai obsoleti, il digitale consente di ottenere dati piu densi e accurati 3D utile per conservazione, restauro, visualizzazione, comunicazione, ecc. Per grandi siti, l integrazione delle tecniche e la soluzione migliore Importanza dei metadata per conservare i dati Mancanza di standard (terminologia, best practices, ecc.) e numeri corretti dal mercato Piu dialogo tra le varie comunita coinvolte nel settore dei beni culturali

GRAZIE Fabio Remondino FBK Trento, Italy Email: remondino@fbk.eu Web: http://3dom.fbk.eu 29