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All 3D images are created or rendered in a virtual space of coordinates and planes. Any objects that are digitally designed within the 3D coordinates can be fully edited in the virtual space, before being manufactured. The coordinate system is a method of assigning numbers to points. In three dimensions, three numbers are required to specify a point. Plain 2D images have numbers related to only two coordinates (x and y). The coordinate that represents the third dimension is usually an axis called z. The z‐axis is perpendicular to both the x‐axis and the y‐axis (Figure 1.2).

The coordinates and the respective planes provide references for the location, size, and volume of the 3D images. All 3D objects have their coordinates fixed in a virtual plane of the imaging software. It is important to make sure that multiple 3D objects to be manipulated or aligned are positioned in the same spatial coordinates, which can be used as spatial references. Therefore, 3D files from different imaging methods should be in the same 3D coordinates in order to be superimposed or combined with the aim of creating a virtual patient, as explained further in this chapter.

Figure 1.2 A 3D object (reconstructed model of a maxillary CBCT scan) is positioned in the 3D space of a software (Ultimaker Cura) to be 3D printed. Note the three axes depicted by the software in different colors (x‐axis in red, y‐axis in green, z‐axis in blue).