1. A computer-readable, non-transitory storage medium storing a program for causing a computer to execute a 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 physical values in elements of the geometric model, which are included in a predetermined range of the voxel, based on a relation between the cross section and first vectors, wherein a first vector of the first vectors is set for one element of a plurality of elements included in the geometric model, the first vectors represent a direction of an inner structure of the object, 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.