Homologous points on the 3D model (left) and the photogram (right) 

Contexts in source publication

Context 1

... obtain texture models with high quality levels for geometry, morphology and colour, that takes advantage of the strictness of 3D models produced from laser scanner surveys, and of the quality of textures derived from sets of photograms oriented with dedicated SfM software. The basic concept is to use laser scanner surveys as the geometric foundation. Regarding the texture, a campaign of dedicated photographs is completed and, rather than orienting and projecting each one individually, SfM software is used not so much for the model that it generates, as for its ability to automatically detect numerous sets of homologous points and to solve the problem of calculating the orientation parameters (camera features). Finally, the model generated by the laser survey is imported in the same SfM software used for camera orientation and the images are projected on it. As a case study for this methodology a frescoed vault under restoration has been chosen. The frescoed surface object of the survey area is a vaulted structure in a room on the ground floor of Palazzo Roncioni in Pisa, one of the finest examples of mannerist architecture of the city (Fig. 1). In addition to architectural merit, the building retains a rich array of decorative painting by Giovan Battista Tempesti, active in Tuscany and especially in Pisa in the second half of the eighteenth century, the author of important frescoes among which we can mention those in the music room at Palazzo Pitti in Florence, and the depiction of the Last Supper in the cathedral of Pisa. The root of the geometric construction of the vault in question relates to the type of italian “a schifo” vaults, set on a rectangular plan of about nine by five meters, although not quite regular. The height from the floor of the top of the vault is about 6m. The fresco is largely preserved, save for obvious, recent gaps due to environmental degradation. The vault also shows widespread injury due to a failure of structural nature. The survey of the vault was required to allow for the documentation of the fresco in view of the restoration work taking place in some portions of the building. LeicaGeosystems’ C10 ScanStation has been used at two spots, located approximately 1/4 and 3/4 lengthwise and both along the centre across the room (Fig. 2 left). The resolution of the survey was set at 4mm at 10m, resulting in a very 2 dense cloud (on average 70pts/cm ). The point cloud is in true colours due to the laser scanner’s built-in camera. After scans have been aligned by means of a support traverse, aided by the cloud constraint tool in the Cyclone software environment, the cloud point was processed by a reverse modelling software (Inus Technology Rapidform XOR3). In order to simplify the model where surfaces were smooth, a decimation of the points was performed, anyway preserving geometrical information that, however small, are valuable for restorers (local deformation, cracks, ...); finally, a mesh was generated. The model is constituted by about four million points and ten million triangles and is the geometric and morphological reference of the final model (Fig. 2 right). The photographic survey was performed with a Nikon D700 SLR camera equipped with a focal lenght 20mm Nikkor lens. ISO sensitivity set to 400 enabled shooting at 1/25 second with 5.6 aperture, also thanks to the lighting provided by a set of two 2000 W halogen lamps with colour temperature of 5600K. The shooting distance was on average of 4.5m, that allowed single pixel coverage of about 2 mm. The camera and its lens have been previously calibrated. Table 1 shows the features of the camera and the results of the calibration. A methodology to provide models with colour maps consisting of photo-realistic textures is based on the projection of the individual photographs on the mesh. Upon completion of the photo campaign, the steps to follow include the collimation of tie points in a reverse modelling software, the collimation of the same points to orient the images using photogrammetric software and finally the definition of the texture through a software for entertainment. In the photographic take draft the surface of the vault has been divided in areas, characterized by almost constant curvature, in each of which photographic images have been acquired, keeping the optical axis close to the direction of the radius of curvature of the centroid of each area. The photograms must ensure full coverage of the object taking into account that only the central portion of each photogram is used in order to avoid residual radial distortion at the edges. The processing procedure is the same for each photogram to be projected. Considering the part in common between the photogram and the 3-D model obtained from the laser scanner, a set of tie points has been chosen with a distribution as uniform as possible. These are exported as coordinates in DXF format, using a point cloud management software of the laser model (eg. Rapidform XOR3, Fig. 3 left). These coordinates constitute the Control Points (CP) which the photogrammetric software (eg. PhotoModeler) uses to orient the photogram. Photogrammetric software is used to derive the image coordinates of the chosen tie points (Fig. 3 right); it is also possible to calculate the camera features along with the precision with which the various parameters were determined. Repeating this process for all the photograms yields the orientation parameters of the cameras, each of which is exported in a format compatible with the entertainment software used for texturing (eg. Luxology Modo - format * .fbx). In order to texturize the model, once it has been imported into the entertainment software, the so-called subdivision surfaces model must be created (Fantini, 2012), and the related UV map is defined (Fig. ...

Context 2

... with dedicated SfM software. The basic concept is to use laser scanner surveys as the geometric foundation. Regarding the texture, a campaign of dedicated photographs is completed and, rather than orienting and projecting each one individually, SfM software is used not so much for the model that it generates, as for its ability to automatically detect numerous sets of homologous points and to solve the problem of calculating the orientation parameters (camera features). Finally, the model generated by the laser survey is imported in the same SfM software used for camera orientation and the images are projected on it. As a case study for this methodology a frescoed vault under restoration has been chosen. The frescoed surface object of the survey area is a vaulted structure in a room on the ground floor of Palazzo Roncioni in Pisa, one of the finest examples of mannerist architecture of the city (Fig. 1). In addition to architectural merit, the building retains a rich array of decorative painting by Giovan Battista Tempesti, active in Tuscany and especially in Pisa in the second half of the eighteenth century, the author of important frescoes among which we can mention those in the music room at Palazzo Pitti in Florence, and the depiction of the Last Supper in the cathedral of Pisa. The root of the geometric construction of the vault in question relates to the type of italian “a schifo” vaults, set on a rectangular plan of about nine by five meters, although not quite regular. The height from the floor of the top of the vault is about 6m. The fresco is largely preserved, save for obvious, recent gaps due to environmental degradation. The vault also shows widespread injury due to a failure of structural nature. The survey of the vault was required to allow for the documentation of the fresco in view of the restoration work taking place in some portions of the building. LeicaGeosystems’ C10 ScanStation has been used at two spots, located approximately 1/4 and 3/4 lengthwise and both along the centre across the room (Fig. 2 left). The resolution of the survey was set at 4mm at 10m, resulting in a very 2 dense cloud (on average 70pts/cm ). The point cloud is in true colours due to the laser scanner’s built-in camera. After scans have been aligned by means of a support traverse, aided by the cloud constraint tool in the Cyclone software environment, the cloud point was processed by a reverse modelling software (Inus Technology Rapidform XOR3). In order to simplify the model where surfaces were smooth, a decimation of the points was performed, anyway preserving geometrical information that, however small, are valuable for restorers (local deformation, cracks, ...); finally, a mesh was generated. The model is constituted by about four million points and ten million triangles and is the geometric and morphological reference of the final model (Fig. 2 right). The photographic survey was performed with a Nikon D700 SLR camera equipped with a focal lenght 20mm Nikkor lens. ISO sensitivity set to 400 enabled shooting at 1/25 second with 5.6 aperture, also thanks to the lighting provided by a set of two 2000 W halogen lamps with colour temperature of 5600K. The shooting distance was on average of 4.5m, that allowed single pixel coverage of about 2 mm. The camera and its lens have been previously calibrated. Table 1 shows the features of the camera and the results of the calibration. A methodology to provide models with colour maps consisting of photo-realistic textures is based on the projection of the individual photographs on the mesh. Upon completion of the photo campaign, the steps to follow include the collimation of tie points in a reverse modelling software, the collimation of the same points to orient the images using photogrammetric software and finally the definition of the texture through a software for entertainment. In the photographic take draft the surface of the vault has been divided in areas, characterized by almost constant curvature, in each of which photographic images have been acquired, keeping the optical axis close to the direction of the radius of curvature of the centroid of each area. The photograms must ensure full coverage of the object taking into account that only the central portion of each photogram is used in order to avoid residual radial distortion at the edges. The processing procedure is the same for each photogram to be projected. Considering the part in common between the photogram and the 3-D model obtained from the laser scanner, a set of tie points has been chosen with a distribution as uniform as possible. These are exported as coordinates in DXF format, using a point cloud management software of the laser model (eg. Rapidform XOR3, Fig. 3 left). These coordinates constitute the Control Points (CP) which the photogrammetric software (eg. PhotoModeler) uses to orient the photogram. Photogrammetric software is used to derive the image coordinates of the chosen tie points (Fig. 3 right); it is also possible to calculate the camera features along with the precision with which the various parameters were determined. Repeating this process for all the photograms yields the orientation parameters of the cameras, each of which is exported in a format compatible with the entertainment software used for texturing (eg. Luxology Modo - format * .fbx). In order to texturize the model, once it has been imported into the entertainment software, the so-called subdivision surfaces model must be created (Fantini, 2012), and the related UV map is defined (Fig. ...