  We present Mesh2NeRF, an approach to derive ground-truth radiance fields from
textured meshes for 3D generation tasks. Many 3D generative approaches
represent 3D scenes as radiance fields for training. Their ground-truth
radiance fields are usually fitted from multi-view renderings from a
large-scale synthetic 3D dataset, which often results in artifacts due to
occlusions or under-fitting issues. In Mesh2NeRF, we propose an analytic
solution to directly obtain ground-truth radiance fields from 3D meshes,
characterizing the density field with an occupancy function featuring a defined
surface thickness, and determining view-dependent color through a reflection
function considering both the mesh and environment lighting. Mesh2NeRF extracts
accurate radiance fields which provides direct supervision for training
generative NeRFs and single scene representation. We validate the effectiveness
of Mesh2NeRF across various tasks, achieving a noteworthy 3.12dB improvement in
PSNR for view synthesis in single scene representation on the ABO dataset, a
0.69 PSNR enhancement in the single-view conditional generation of ShapeNet
Cars, and notably improved mesh extraction from NeRF in the unconditional
generation of Objaverse Mugs.
