Abzal, A.,
Saadatseresht, M.,
Varshosaz m., M. Photogrammetric Record (14779730)34(165)pp. 63-84
This paper proposes a new fringe projection scanner that uses a dual pattern to prevent phase retrieval errors or complications. The pattern comprises two horizontal and vertical patterns, however, just one of them is involved in computing the coordinates of an object point. To define the pattern, a photometric stereo component is used to extract the geometric properties of the object. The extracted data is employed to form a decision mask, each pixel of which defines the best pattern (horizontal, vertical or both) related to one of the object points. In this way, the scanner determines which pattern to use to obtain the most accurate results. Experiments suggest not only the avoidance of phase retrieval problems, but also an increase in the accuracy of the measurements (by 56% in this test). © 2019 The Authors. The Photogrammetric Record © 2019 The Remote Sensing and Photogrammetry Society and John Wiley & Sons Ltd
Abzal, A.,
Saadatseresht, M.,
Varshosaz m., M. CTIT workshop proceedings series (16821750)42(4/W18)pp. 7-12
Geometric documentation is one of the most important parts of a documentary report. Despite the advances made in the field of line drawing of ancient relief surfaces, in most cases, human operator interaction is unavoidable. In this paper, an algorithm for the semiautomatic line drawing of relief surfaces has been developed. In the proposed method, photometric stereo normals are used as a highresolution and low-noise data for the automatic extraction of surface edges. The normals are computed in 2D image space and also the fringe projection scanner is used for geometric correction of 2D image based drawings. Therefore, the drawings are converted to a metric map for geometric documentation reports. The results show that the efficiency of the proposed method, which has managed to correctly draw about more than 99% of the edge lines of an ancient relief. Also all of the drawn lines are completely coincided to the relief edges on its orthophoto image. © 2019 A. Abzal et al.
Abzal, A.,
Saadatseresht, M.,
Varshosaz m., M. ISPRS Journal of Photogrammetry and Remote Sensing (09242716)142pp. 12-20
Most optical scanners work based on a fix resolution and, thus, produce a huge number of points, many of which are usually redundant. Therefore, an intensive post-processing step is required to simplify the resulting point cloud. In this paper, a novel technique is proposed that does not require the post-measurement calculations; instead, it reduces the scanned points at the data-acquisition phase. For this, the surface curvatures of object points are determined using the photometric stereo. Then, the curvature values are classified based on an adaptive sampling interval which is defined through an innovative calibration process. Once the curvature ranges are identified as such, a simplification mask is created. The mask is a binary image that is used to show points in the image space the optical scanner requires to decide if the 3D coordinates of an object point need to be computed. Having evaluated the proposed method using a fringe scanner, we observed that, although the data acquisition time is slightly increased, the number of redundant points is notably reduced. Therefore, not only the production of unnecessary data is prevented by 71–90% (depending on the surface complexity), but also carrying out the intensive post-processing simplification step is totally avoided. © 2018
Advanced Materials Research (discontinued) (16628985)301pp. 388-396
Cyclic axial loads in steel tubular might lead to local buckling, wrinkling and accumulation of plastic strains in the tube. During their life time steel tubes may also experience different types of material loss such as corrosion or thinning. This paper deals with the effects of corrosion defects on the strain ratcheting response of steel tubes. Small scale un-corroded and corroded tubular specimens have been tested under monotonic and cyclic axial loads. Optical system ATOS has been used for 3D surface acquisition and reconstruction of the tested specimen and to evaluate their strain ratcheting and wrinkling response. This is a camera-based triangulation system. A processing unit employs optical transform equations to automatically and with a great accuracy calculate 3D coordinates for every pixel of camera. Depending on camera resolution as an effect of such a scan a cloud of up to 4 million points has been obtained for every single measurement. From the results, it has been noticed that the possibility of ratcheting or progressive plastic failure substantially increases by the presence of the corrosion defects. With the corroded specimens, the strain ratcheting behaviour in the defected zone has been distinctively different from that in the perfect zones.
Abzal, A.,
Varshosaz m., M.,
Saadatseresht, M. Photogrammetric Record (14779730)26(135)pp. 293-306
In this paper a new triangulation-based laser scanner is presented which has a simple, yet strong, flexible and low-cost structure. A digital camera and three laser line projectors are the main components of the system. One of the laser projectors is positioned vertically, while the other two are horizontal. The former scans the object, whereas the latter two establish an optical frame which is used, in part, to define the plane containing the vertical laser projector at each step of scanning. At each step, an image is taken which includes the object along with the projected laser lines. By intersecting the vertical and horizontal lines a couple of points are formed which, along with the calibration information of the system, enable the extraction of the object coordinates. Results of the tests carried out show that by using an optical frame of this nature, the process of scanning is greatly facilitated. That is, the scanner can easily be used to scan objects of different size and dimensions. Within the current configuration, the system enables measurements with an accuracy of 1/1600. Also, as the system has a rigorous basis, its accuracy can be increased if improved hardware is provided. © 2011 The Authors. The Photogrammetric Record © 2011 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd.
