  Pre-transitional disks are protoplanetary disks with a gapped disk structure,
potentially indicating the presence of young planets in these systems. In order
to explore the structure of these objects and their gap-opening mechanism, we
observed the pre-transitional disk V1247 Orionis using the Very Large Telescope
Interferometer, the Keck Interferometer, Keck-II, Gemini South, and IRTF. This
allows us spatially resolve the AU-scale disk structure from near- to
mid-infrared wavelengths (1.5 to 13 {\mu}m), tracing material at different
temperatures and over a wide range of stellocentric radii. Our observations
reveal a narrow, optically-thick inner-disk component (located at 0.18 AU from
the star) that is separated from the optically thick outer disk (radii >46 AU),
providing unambiguous evidence for the existence of a gap in this
pre-transitional disk. Surprisingly, we find that the gap region is filled with
significant amounts of optically thin material with a carbon-dominated dust
mineralogy. The presence of this optically thin gap material cannot be deduced
solely from the spectral energy distribution, yet it is the dominant
contributor at mid-infrared wavelengths. Furthermore, using Keck/NIRC2 aperture
masking observations in the H, K', and L' band, we detect asymmetries in the
brightness distribution on scales of about 15-40 AU, i.e. within the gap
region. The detected asymmetries are highly significant, yet their amplitude
and direction changes with wavelength, which is not consistent with a companion
interpretation but indicates an inhomogeneous distribution of the gap material.
We interpret this as strong evidence for the presence of complex density
structures, possibly reflecting the dynamical interaction of the disk material
with sub-stellar mass bodies that are responsible for the gap clearing.
