1. A computer-readable, non-transitory storage medium storing a program for causing a computer to execute a process, the process comprising: performing a processing for adjusting positions of voxel data for an object and data of a geometric model for the object; calculating, for each voxel included in a range defined by a cross section among a plurality of voxels that are included in the voxel data, a voxel value of the voxel from weighted physical values that are obtained by weighting, for each of elements of the geometric model, a physical value that is set in the element, according to a length of a first vector obtained when projecting a second vector that is set for the element and represents a direction of an inner structure of the object onto the cross section, wherein the elements are included in a predetermined range of the voxel, and the cross section is set for the voxel data and the geometric model data; and rendering an image by using the voxel value calculated for each voxel.