## 4 Discussion
When considering the case of significant decompensation of scoliosis, the obtained X-ray image could show the patient's body's asymmetrical alignment to the \(y\)-axis. The projection of the patient's center of gravity on the \(x\)-axis may not be approximately at the center of the coordinate system but some distance from it. Therefore, after performing the translation \(T\Big{(}P_{IC(x)}\Big{)}\), the cloud of points will be shifted concerning the image. In the worst scenario, the patient's positioning during the X-ray is significantly different from the positioning during the 3D ST measurement. In this case, even manual adjustment of the data will be impossible, and the method will fail. The small difference in the patient's body's slope in the _xy_ plane between X-ray and 3D ST measurements will slightly deform the calculated line's shape. Small gradients characterize the curvature of the back in humans. Therefore, a slight shift of the computed points' position on the dorsum's surface causes deformation in the shape of the line in the order of a few millimeters. Smaller rotations of the patient's body of less than 45\({}^{\circ}\) in the _xz_ plane are acceptable and can be compensated by rotation \(R_{(y)}\left(-\theta_{(y)}\right)\). More extensive rotations are unacceptable because the simplified approach used to calculate the best-fit plane fails. The inclination of the patient's body in the _yz_ plane can be compensated by rotation \(R_{(x)}\left(-\theta_{(x)}\right)\). It is unlikely that the inclination angle will be greater than 45\({}^{\circ}\) when the patient stands freely without any support. The position of the center of the mass of the cloud of points \(P_{\text{MC}}\) depends on the shape of the cloud. The cloud of points should represent only the patient's trunk, as the head and legs, and any asymmetrical areas without points, can change the position of \(P_{\text{MC}}\) and influence the result of the best-fit plane calculation. The average difference of 5 mm makes the method unsuitable for surgery planning. In this field, spatial radiological imaging methods, such as computed tomography, will probably remain unrivaled for a long time. The study aimed to develop a method that will visualize the vertebrae's spinous processes with a good approximation based on a single radiological image, thus supporting the diagnosis. The spine line's orthogonal projection from the X-ray image onto a point cloud was used in the proposed method. There are several limitations to this study. First, it uses a single anteroposterior X-ray view of the spine. Therefore, the effectiveness of reducing exposure to X-rays is not entirely convincing. The effectiveness may be 50% only when biplanar radiograms are needed. Second, the study analyses were based on the cases with a relatively small Cobb angle. The authors do not discuss the method's final effectiveness in patients with greater curvatures who are eligible for surgery. Similarly, the study results were not compared to patients with a high BMI, nor was scoliosis classification made in accordance with Lenke [83] (main thoracic, double thoracic, double major, triple major, single structural, or thoracolumbar/lumbar-main thoracic double curves). Third, accurate geometric data on the X-ray examination performance should be known and taken into account, such as the X-ray lamp's position in relation to the detector and the X-ray radiation course during exposure. The exact design parameters of the X-ray apparatus would have to be known. Moreover, it should be ensured that the examined person adopts the same body position during the 3D scanning as during the X-ray examination. Regardless of this, during the 3D measurement, one can palpate characteristic points, such as those clearly visible on X-rays and easily palpable, such as the shoulder process, the C7 spinous process, the lower angles of the scapula, and the L4 spinous process. It is possible to register images accurately using well-marked characteristic points.