Circumstellar disks (CS) are ubiquitous around stars with intermediate ages around a few 
millions years. They are the natural outcome of the star formation process because of the 
angular momentum conservation during the collapse of the initial molecular core.  As the 
system evolves, the gas phase dissipates and properties of the dust dramatically change from 
small interstellar grains to eventually coagulate into constitutive building blocks 
(planetsimals) of planetary systems.  Dust grains sizes are modified by dust settling in
CS disks also as chemical composition, going from amorphous to crystalline phase probably 
because of annealing processes.  Herbig Ae stars represent a particularly interesting 
laboratory for studying disks evolution and planet formation. They are the more massive 
(2-10 solar masses) analogues of T Tauri stars. They are the progenitors of the debris disks 
around A stars (like Beta Pictoris) and were comprehensively studied by the infrared 
spectrometer (ISO-SWS) on board of the ISO telescope.  
                     
Although large progress have been made in modelling the disks structure using radiative 
transfer models (Chiang & Goldreich, 1997, Natta et al., 2001, Dullemond & Dominik, 2001), 
the structure of these disks is not uniquely constrained by their source energy distribution 
(SED) which is in most of the cases, the only observational constraint available up to now.  
Spatially resolved observations are then essential to bring strong contraints on the disk
geometry.  
                     
The VISIR instrument is the recently installed mid-infrared imager and spectrometer 
instrument, attached to the telescope Melipal at VLT observatory (Paranal, Chile). Using 
this instrument, we have conducted a key program of observations dedicated to the study of 
such HAe disks, using high angular observations (0.3 arcsec at 10 microns) in imaging and 
spectrometry . Thanks to these observations, we could spatially resolve a significant 
fraction of these disks and replace the results in the framework of group I and II disks as 
defined by Meuus, 2001.  A spectacular flaring disk was found around HD97048, detected up to 
angular distances of more than 3 arcsec (about 500 AU). Its nicely resolved image allows for 
the first time to constraint directly the disk geometry. Results of the modeling of this
disk such as inclination, disk mass, surface density, flaring index; will be presented.