Section: New Results
Computer Graphics (in collaboration with LIAMA)
As planned in 2008, activities in Computer Graphics in this term shows significant topic changes. LoD model developments are nearly closed while activities related to 3D reconstructions do increase as well as studies involving GPU and Web visualisation. Specific new trends are also explored, involving high level structural and on functionnal data. Scientific animation is also developping, a networking project VLS-LRC has gained supports of Agropolis fondation and INRIA, to develop a regional network (from Barcelona to Montpellier) involving key players on Virtual Landscape visualisation and their applications.
Simple plant LOD models and real time plant rendering (with LIAMA)
Level of Detail single plant models, based on simulator Line Tree output has shown few new developments in the last period. Both Digiplante and associate team (Dr. Xiaopeng Zhang and his students in LIAMA) do consider that this subject is mature and entering in a valorization process. Focus was thus given on common tool specification and writting, especially on tools generating tree structures. French and Chinese plant growth simulator 3D ouput (line trees) were normalized. A graphical tool "LIGDRAW" dedicated to single tree visualisation and graphical material property definitions was designed by M. Jaeger. This tool also aims to host wrappers between several representation, allowing conversions of line-trees to LOD models (branches only so far). The tool is already used at ECP and LIAMA. This engineering work (Qt based) is still ongoing.
Real time visualisation involving strongly GPU techniques (with LIAMA and BJFU)
GPU techniques are more and more explored with the help of Yang Gang specialist of BJFU (Image and Graphics lab, Beijing). This year, two main threads were explored: use of GPU for simple shape rendering and Use of GPU for real time shadow computations On this last subject, the work is a simple extension on past results gained last year on foliage and instanciations. The approach uses the classical depth map; the contribution lies on the computation of the appropriate LOD Model constrained by two views (camera and light) Concerning basic shapes. The idea is to send to the GPU the 3D skeleton of the plant and not the 3D geometry mesh. Up to know, we could defined tools generating 2D 1/2 shapes (ellipsoids and branch pieces) from single skeletons. The results are promissing, and will go on (no publication so far)
3D reconstruction from images and laser scans (with LIAMA)
This topic has shown significant progress at LIAMA. In the collaboration with DigiPlante, the work mainly adresses reconstruction from 3D laser scans. On tree crown shapes, PhD of Zhu Chao made progress on crown shape reconstruction (alpha shapes). The 3D point cloud of the full tree is segmented in different clusters, based on distance to trunk and main branch identification. This preprocess speeds up the 3D crown reconstruction (since not linear) and gives better results, extracting a colony of crowns instead a single one. Nice progress were also gain on point cloud segmentation, using combinaisons of three different criteria: distance, local normals, local curvatures. Depending on the target of the reconstruction, those criteria are combined differently in order to cluster and then segment objects in the point range scene. Two specific cases where detailled: building and vegetation extractions from large scenes, and foliage/branch classification on single trees. This area led to several publications at PMA09, ICGVR and VRCAI conferences.
Exploring new ways of single plant visualisation (with AMAP)
With the development of new simulators packages, new internal structures and disk output are available. Especially data allowing stop and go actions, representing the simulated plant with a flat metamer graph and its functional properties (leaf volume, metamere volume, pith volume) can be used to generate the plant geometry. First tries were hold on this point, defining metamere lengths and diameters from production.With simple angle rules, and allometry rules, we show that we could easily generate 3D outputs from this very compact internal data structure. This preliminary study is promising.
There is still some work hold in this area, mainiy valorizing past experiences. The team and associated team was invited to publish an extended paper on tree structure extractions form voxel shapes, on the basis of the publication to VRCAI conference (an is related journal IJVR)  . This collaborative work hold on voxel image tree data hierachical segmentation should be edited soon as book chapter in Pattern Recognition (Springer Ed).