In dentistry, 3D IOS (intra-oral scanners) are gaining an increasing popularity essentially for the production of dental prostheses. Until now, there is no normalized procedure to determine the resolution of IOS. Such a procedure could be a positive parameter for the IOS market and a first step in their normalization. The aim of this study is to present a reproducible methodology to estimate the noise and resolution of any type of IOS. For the noise, we used the IOS Trios 2 (3Shape) and the Carestream 3500 (Carestream) for noise and resolution. As reference, we used an ultra-flat and ultra-smooth alumina. Being perfectly flat, any record of roughness should be interpreted as noise. In this study, the root mean square (RMS) values obtained are ranged between 5.29 and 12.58 micrometers. Significant differences have been found between the central part and the whole mesh. This is due to edge effect: deviation from a flat surface is more important on the edge of meshes than the internal part. To evaluate the resolution, a ceramic tip, well-polished was recorded with the IOS’s and compared to the mesh obtained with micro tomography (5 micrometer resolution). We measured the distance between the two plans of the tip, considered as the small detail recorded. We found a distance from 89 to 121 micrometers with IOS studied and 25 micrometers with micro CT. Those methods, simple and reproducible, could be perfectly suitable to evaluate and compare commercial all types of IOS’s.
Nowadays, most of the manufactured objects are designed using CAD (Computer-Aided Design) software. Nevertheless,
for visualization, data exchange or manufacturing applications, the geometric model has to be discretized
into a 3D mesh composed of a finite number of vertices and edges. But, in some cases, the initial model may be
lost or unavailable. In other cases, the 3D discrete representation may be modified, for example after a numerical
simulation, and does not correspond anymore to the initial model. A reverse engineering method is then required
to reconstruct a 3D continuous representation from the discrete one.
In previous work, we have presented a new approach for 3D geometric primitive extraction. In this paper, to
complete our automatic and comprehensive reverse engineering process, we propose a method to construct the
topology of the retrieved object. To reconstruct a B-Rep model, a new formalism is now introduced to define the
adjacency relations. Then a new process is used to construct the boundaries of the object. The whole process is
tested on 3D industrial meshes and bring a solution to recover B-Rep models.
KEYWORDS: Digital watermarking, Steganography, Data hiding, Multimedia, Symmetric-key encryption, 3D applications, Lawrencium, Multimedia encryption, 3D displays, Televisions
Multimedia protection is one of the main research challenges in computer sciences. We can encrypt the media
in order to make the content unreadable without a secret key of decryption, protect the file with Digital Right
Management (DRM), or embed an hidden message in the file (watermarking and steganography). We are
interested in data hiding applications for 3D mesh. In this domain, there are various problems, of which the
synchronization of the message in the support host. The synchronization is the operation that allows to scan a
mesh with a unique path and by selecting the same areas (vertices, triangles, quadrangles, for example) before
and after the embedding even if the mesh has been noised. In this paper, we propose a new synchronization
approach based on feature point selection in a low resolution of the 3D object. The building of the low resolution
is made by decimation and the feature point selection is based on the discrete curvature computing. We evaluate
the robustness of the synchronization in the low resolution and in the high resolution.
KEYWORDS: 3D modeling, Digital watermarking, Data hiding, Multimedia, 3D image processing, Space reconnaissance, Data modeling, 3D metrology, Lead, Video
Synchronization in 3D data hiding is one of the main problems. We need to know where we can embed information,
and be able to find this space in order to extract the message. Various algorithms propose synchronization
techniques by triangle or vertex path in a 3D mesh. In this paper, we proposed a new synchronization technique
based on Euclidean minimum spanning tree computing (EMST) and the analysis of the displacement of
the vertices without moving the connections in the tree. Based on the analysis of the vertices, we select the
most robust vertices and synchronize these areas by computing a new EMST called "robust EMST". Then, we
analyze the robustness of the technique, i.e. the stability of the most robust vertices selection; and demonstrate
the consistence of the criterion selection with the vertex displacement.
In an industrial context, recovering a continuous model is necessary to make modifications or to exchange
data with a format including continuous representation of objects like STEP. But for many reasons, the initial
continuous object can be lost after a display or an exchange with a discretized format. The mesh can also be
deformed after a numerical computation. It is then important to have a method to create a new continuous
model of the object from a mesh. In case of CAD object, the first step is to detect simple primitives like: plane,
sphere, cone and cylinder from a 3D CAD mesh. This paper is focused on this step. This method of detection
use curvature features to recover each primitive type. Segmentation is based on the curvature feature computed
for each vertex. It permits to extract sub-meshes. Each one corresponds to a primitive. Parameters of these
primitives are found with a fitting process according to the curvature features.
KEYWORDS: Visualization, Digital watermarking, Steganography, Electroluminescence, Data hiding, 3D image processing, Databases, Internet, Multimedia, Clouds
In 3D steganography and watermarking, the synchronization of the hidden data is a major problem. We need
to know where the message is embedded in order to extract the correct information. Various algorithms have
been proposed for the last couple of years and we focused on a method based on Euclidean minimum spanning
tree (EMST) for the mesh vertices. In this paper we analyze the sensitivity of the EMST structure in order
to propose a new method more robust. We present a new theoretical analysis and we propose to visualize the
robustness of the EMST. Moreover, we can apply this analysis to various applications that can be useful in 3D
steganography such fragile area detection and prediction of the 3D object robustness during transmission on a
noisy channel.
The design of representative models of the human body is of great interest to medical doctors. Qualitative information about the characteristics of the brain is widely available, but due to the volume of information that needs to be analyzed and the complexity of its structure, rarely is there quantification according to a standard model. To address this problem, we propose in this paper an automatic method to retrieve corresponding structures from a database of medical images. This procedure being local and fast, will permit navigation through large databases in a practical amount of time. We present as examples of applications the building of an average volume of interest and preliminary results of classification according to morphology.
We present a craniofacial surgery simulation testbed that makes extensive use of virtual reality techniques. The skull, skin and fat tissues are represented with simplex meshes, that are characterized with a constant vertex to vertex connectivity. Surfaces and volumes are respectively described as three and four connected meshes. This representation is well suited for the implementation of surface deformations such as those exerted on the face skin under the action of fat tissues. Furthermore, cutting surface regions may be easily achieved due to the local nature of simplex meshes. The user proceeds by cutting skull fragments and reorganizing them with the help of a virtual hand. Fat tissue attached to both skin and skull adjusts the face shape to the reconstructed skull.
This paper presents a general scheme for the building of anatomical atlases. We propose to use specific and stable features, the crest lines (or ridge lines) which are automatically extracted from 3D images by differential geometry operators. We have developed non-rigid registration techniques based on polynomial transformations to find correspondences between lines. We got encouraging results for the building of atlases of the crest lines of the skull and of the brain based on several CT-Scan and MRI images of different patients.
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