Seminars of LAMA
Four regular seminars take place at LAMA, in the seminar room, first floor of the building Le Chablais, (see How to come ?).
Weekly seminars:
- Seminar of the EDPs2 team, usually on Fridays, at 3pm.
- Seminar of the Geometry team, usually on Thursdays, at 4pm.
- Seminar of the LIMD team, usually on Thursdays, at 10:15, common with the Plume team (ENS Lyon).
Others seminars
- Department’s seminar
- Seminar of phd students
- The CMI seminar: It welcomes a researcher presenting its work to student following the Master Ingenior Cursus (CMI).
- Seminars of the labs members of the MARA federation:
Next seminars:
LIMDThursday 7th July 2022 at 10h
Jacques-Olivier Lachaud
(LAMA),
An alternative definition for digital convexity
Abstract: (Hide abstracts)
This talk proposes full convexity as an alternative definition of digital convexity, which is valid in arbitrary dimension. It solves many problems related to its usual definitions, like possible non connectedness or non simple connectedness, while encompassing its desirable features. Fully convex sets are digitally convex, but are also connected and simply connected. They have a morphological characterisation, which induces a simple convexity test algorithm. Arithmetic planes are fully convex too. Full convexity implies local full convexity, hence it enables local shape analysis, with an unambiguous definition of convex, concave and planar points. We propose also a natural definition of tangent subsets to a digital set. It gives rise to the tangential cover in 2D, and to consistent extensions in arbitrary dimension. We present two applications of tangency: the first one is a simple algorithm for building a polygonal mesh from a set of digital points, with reversibility property, the second one is the definition and computation of shortest paths within digital sets. In a second part of the talk, we study the problem of building a fully convex hull. We propose an iterative operator for this purpose, which computes a fully convex enveloppe in finite time. We can even build a fully convex enveloppe within another fully convex set (a kind of relative convex hull). We show how it induces several natural digital polyhedral models, whose cells of different dimensions are all fully convex sets. As perspective to this work, we study the problem of fully convex set intersection, which is the last step toward a full digital analogue of continuous convexity.