A clean, robust 3D medial axis

Computing the medial axis of a 3D surface mesh is challenging. Points on the discrete medial axis can be defined as interior Voronoï vertices of the surface mesh, but the resulting medial structure rarely has clean connectivity and consistent geometry. In this paper, we provide a medial axis computation based on the Voronoï diagram able to generate manifold medial sheets with coherent topology and geometry, generating consistent geometric structures similar to those in the continuous setting. Because of the correspondences between the surface mesh and resulting medial mesh, we also provide an efficient way to separate the shape into coherent regions associated to medial structures. This correspondence allows for a medial-axis-based filtration of surface structures to generate a Hausdorff ε-approximation of the surface points based on a simplified medial axis, thereby providing a robust medial representation with guaranteed surface approximation

One-step compact skeletonization

International audienceComputing a skeleton for a discretized boundary typically produces a noisy output, with a skeletal branch produced for each boundary pixel. A simplification step often follows to reduce these noisy branches. As a result, generating a clean skeleton is usually a 2-step process. In this article, we propose a skeletonization process that produces a clean skeleton in the first step, avoiding the creation of branches due to noise. The resulting skeleton compares favorably with the most common pruning methods on a large database of shapes. Our process also reduces execution time and requires only one parameter, ε, that designates the desired boundary precision in the Hausdorff distance

A Salience Measure for 3D Shape Decomposition and Sub-parts Classification

International audienceThis paper introduces a measure of significance on a curve skeleton of a 3D piecewise linear shape mesh, allowing the computation of both the shape's parts and their saliency. We begin by reformulating three existing pruning measures into a non-linear PCA along the skeleton. From this PCA, we then derive a volume-based salience measure, the 3D WEDF, that determines the relative importance to the global shape of the shape part associated to a point of the skeleton. First, we provide robust algorithms for computing the 3D WEDF on a curve skeleton, independent on the number of skeleton branches. Then, we cluster the WEDF values to partition the curve skeleton, and coherently map the decomposition to the associated surface mesh. Thus, we develop an unsupervised hierarchical decomposition of the mesh faces into visually meaningful shape regions that are ordered according to their degree of perceptual salience. The shape analysis tools introduced in this paper are important for many applications including shape comparison, editing, and compression

Research in Shape Analysis: WiSH2, Sirince, Turkey, June 2016

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Perinatal specimens of <i>Saurolophus angustirostris</i> (MPC-D100/764).

<p>Calcified cartilage (close-up of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138806#pone.0138806.g010" target="_blank">Fig 10</a>). Calcified cartilage preserved as small transparent and translucent globules with sizes in the order of a few tens of micrometers. Orange-brown matter is hematite dispersed within the cones of calcified cartilage, but especially concentrated at the contact surface between the calcified cartilage and the bone tissue. Inset: location of the close-up within the bone.</p

Perinatal Specimens of <i>Saurolophus angustirostris</i> (Dinosauria: Hadrosauridae), from the Upper Cretaceous of Mongolia

<div><p>Background</p><p>The Late Cretaceous Nemegt Formation, Gobi Desert, Mongolia has already yielded abundant and complete skeletons of the hadrosaur <i>Saurolophus angustirostris</i>, from half-grown to adult individuals.</p><p>Methodology/Principal Findings</p><p>Herein we describe perinatal specimens of <i>Saurolophus angustirostris</i>, associated with fragmentary eggshell fragments. The skull length of these babies is around 5% that of the largest known <i>S</i>. <i>angustirostris</i> specimens, so these specimens document the earliest development stages of this giant hadrosaur and bridge a large hiatus in our knowledge of the ontogeny of <i>S</i>. <i>angustirostris</i>.</p><p>Conclusions/Significance</p><p>The studied specimens are likely part of a nest originally located on a riverbank point bar. The perinatal specimens were buried by sediment carried by the river current presumably during the wet summer season. Perinatal bones already displayed diagnostic characters for <i>Saurolophus angustirostris</i>, including premaxillae with a strongly reflected oral margin and upturned premaxillary body in lateral aspect. The absence of a supracranial crest and unfused halves of the cervical neural arches characterize the earliest stages in the ontogeny of <i>S</i>. <i>angustirostris</i>. The eggshell fragments associated with the perinatal individuals can be referred to the <i>Spheroolithus</i> oogenus and closely resemble those found in older formations (e.g. Barun Goyot Fm in Mongolia) or associated with more basal hadrosauroids (<i>Bactrosaurus</i>-<i>Gilmoreosaurus</i> in the Iren Dabasu Fm, Inner Mongolia, China). This observation suggests that the egg microstructure was similar in basal hadrosauroids and more advanced saurolophines.</p><p>Competing Interests</p><p>One of the authors (FE) is employed by the commercial organization Eldonia. Eldonia provided support in the form of a salary for FE, but did not have any additional role or influence in the study design, data collection and analysis, decision to publish, or preparation of the manuscript and it does not alter the authors’ adherence to all the PLoS ONE policies on sharing data and materials.</p></div

Perinatal specimens of <i>Saurolophus angustirostris</i> (MPC-D100/764).

<p>Articulated skull in right lateral view, partial braincase in left lateral view and cervical vertebrae. (A) without and (B) with bone identification. Color labels in (B) indicate: premaxilla (azure blue), maxilla and teeth (drab pink), nasal (navy blue), lacrimal (brown), jugal (white), prefrontal-supraorbital (olivine), postorbital (lilac), predentary (blue), dentary (green), frontal (orange); parietal (purple), laterosphenoid (drab yellow), prootic (apricot orange), exoccipital (moss green), occiput and cervical vertebrae (red), humerus (yellow), indeterminate material or skeletal debris (black). Cranial nerves V and VIII are indicated on (B).</p

Sediments surrounding the <i>Saurolophus angustirostris</i> perinatal specimens MPC-D100/764.

<p>Intraformational pebbles set apart from matrix by differences in color and relief of sawing plane. Intraformational pebbles indicated by white arrows.</p

Cranial ontogenetical changes in <i>Saurolophus angustirostris</i>, as listed by Maryanska and Osmolska [11], with incorporation of observations on the hatchling specimens.

<p>Additional changes that occured early in ontogeny and could not be observed in later development stages concern the development of the supracranial crest and the fusion of the left and right halves of the neural arches.</p><p>Cranial ontogenetical changes in <i>Saurolophus angustirostris</i>, as listed by Maryanska and Osmolska [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138806#pone.0138806.ref001" target="_blank">1</a><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138806#pone.0138806.ref001" target="_blank">1</a>], with incorporation of observations on the hatchling specimens.</p