Application of our bubble-finding procedure to a 3D simulation. Left: 2D slices through the ionization field. Ionized/neutral regions are shown in white/black. The brightest galaxies in this 1.5 cMpc slice are denoted with stars, colored according to their UV magnitudes. The line-of-sight direction used to compute the IGM opacity for each observed galaxy is indicated with the arrow. The 20×20×20 cMpc subvolume used for the mock survey is denoted with the red square. Right: Zoom-in of the mock survey. A random subsample (to avoid overcrowding) of the observed galaxies is shown with stars. Ionized voxels are shown in gray. Our maximum likelihood solution for the central HII bubble is overlaid with the blue sphere. The reasonable overlap of the central gray blob with the blue sphere shows that our framework is reliable.