Proceedings of the CIPA WG 6 International Workshop on Scanning for Cultural Heritage Recording

Böhler, Wolfgang

Bibliographic data

Monograph

Persistent identifier:: 830281592

Title:: Proceedings of the CIPA WG 6 International Workshop on Scanning for Cultural Heritage Recording

Sub title:: September, 1 - 2, 2002, Corfu, Greece

Scope:: 159 Seiten

Year of publication:: 2002

Place of publication:: Thessaloniki

Publisher of the original:: Publ. ZITI

Identifier (digital):: 830281592

Illustration:: Illustrationen

Signature of the source:: T 15 B 1303

Language:: English

Additional Notes:: Literaturangaben

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: Böhler, Wolfgang

Corporations:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Adapter:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Founder of work:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Other corporate:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2015

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: 5. PROJECTS AND EXPERIENCES

Document type:: Monograph

Structure type:: Chapter

Chapter

Title:: LASER SCANNING AND TRADITIONAL SURVEY INTEGRATION TO BUILD A COMPLETE 3D DIGITAL MODEL OF "SAGRESTIA DELL'ARCHIVIO DI STATO A MANTOVA". Roberto Cantoni, Giorgio Vassena, Carlo Lanzi

Document type:: Monograph

Structure type:: Chapter

- 106 - scanning parameters (occlusion detection, accuracy, time optimisation...) All these reasons underline how is important to use digital instruments during the survey that allow to verify on the field, in real time, the data transferred on a portable PC and evaluating the best position of the point of view for the next scan or intensity image acquisition. Figure 1. Scan field of view on sacresty plan. The distance, between the center of the sensor and the points on the surfaces, has remains between 10 and 15 meters, so considering that the laser mesh was composed from 1000x1000 points with an aperture of 40°x40°, the distance between the points, in the cloud that describes the 3D model, result included between 1cm and 1,5cm. The whole process of evaluation to create a 3D model took about 7 days, fairly divided between geometrical mesh construction and textures application. A reconstruction algorithm based on polygonal meshes was used to produce a triangulated model. Figure 2. Triangulated model of a scan. To map the texture upon the surface covered from a single scan, has been necessary two photographic images taked from a position close to the laser scanner viewpoint. The digital camera adopted is CANON Powershot PRO 90 IS with CCD 3,34 Mpixel sensor. One possible solution for determining the relationship between range and color images is through calibration using the calibration board and fixtures. However, this method requires that the range and color sensors be fixed on the fixture once the relationship is calibrated. But usually a color camera is much handier than a range sensor so is better to take color images freely without having to transport a heavy and fragile range sensor. As side product of range images, range sensor often provide reflectance images that represent a collection of the strenght of returned laser energy at each pixel. This image is aligned with the range image because both images are obtained through the Figure 3. Reflectance image of a scan. same receiving optical device, in other words reflectance and range data are fully registered, considering they both originate with the same echoed laser. The returned timing provides a depth measurement, while the returned strength provides a reflectance measurement. A reflectance image is itself an image of the scene and can be matched to any other image such as photographic images. Our range sensor Cyrax provide reflectance image, so we decided to employ this image as a vehicle for the alignment of range images with intensity images. Reflectance images are similar to intensity images in that both images are somehow related by surface roughness. Since the reflectance image is aligned with the range image, so to align the reflectance image with the intensity image is much easer task than that aligning the range image with the intensity image. Corrispondences between the reflectance and the digital images are computed using a semi-automatic system, that align extracted features (edges or points) from reflectance images with those in intensity images. It is possible to guide the system by adding extra points and find further corrispondences. These edges are easy to find in the intensity images, since they are generates from a boundary between two different colors or materials that generates a discontinuity of reflectance. Thus, this method allows to align 3D points on range surfaces with 2D points in the intensity images. This is very flexible in that it allows the model to be texture-mapped using an image taken with any camera, at any time (even historic images can be uesed), from any location. The software used to process the laser scanner data is RECONSTRUCTOR realized by 3Dveritas.

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