To give an illustration of the physical phenomenon, three typical movies of the
floating spheres seen from top are available in mpg format, with a projection
speed multiplied by ten. First one ('movie1.avi') corresponds to 328 particles
and a change of the area fraction from 0.20 to 0.63, second one to 688 particles
and a change of area fraction from 0.33 to 0.65 and then third one to 1139
particles and a change of area fraction from 0.46 to 0.71. Moreover
complementary information are presented in the file 'suppl.pdf'. First to
justify the homogeneity of compression, we provide a figure plotting the mean
number of particles per unit area as a function of radial distance from the
center axis of the funnel. Then we give a complementary analysis of system
heterogeneity by plotting the distribution of shape factor of Voronoi cells.
Finally we present a pore size analysis.