The study illustrates the solution of the three point space resection problem, treated by Gaspard Monge in Section V of Leçons de Geometrie Descriptive. The problem entails the construction of the intersection curves of three tori. To solve this problem, Monge introduces several simplifications but, nevertheless, makes a mistake; this mistake has already been pointed out by Gino Loria regarding the number of solutions allowed by the problem. The mathematical representation, thanks to its high level of accuracy, today permits not only an efficacious solution of the general case, it also highlights without difficulty the right number of solutions. We applied this theory to a case of photogrammetric rendering, difficult to carry out by means of the tools offered by commercial software. Case in question concerns the reconstruction of the architectural volumes, now lost, which were located along the road that crosses a village, near Rome. As is known, the reconstruction of points in space from two images is possible if these images are projective and we have at least two projective orientated stars. The first image is a vintage photograph (1892), the second image is a surveyed plan of the masonry still present at the site. Therefore, one of the two projective stars is assimilated to a class of vertical straight lines. With regard to photography, the problem is articulated in two typical phases of photogrammetric processes: internal orientation and absolute orientation. For the absolute orientation we used the pyramid vertex method, in use since the Eighteenth Century, which consists in determining the projection center from three given points of which the positions in space are known. The solution to the problem posed by the case study can be considered as a useful result. More interesting, however, is the result of the intersection of the three tori with the incident axes. It is, in fact, a graphic process that Gaspard Monge had already proposed in 1798 as a suitable alternative to a system of equations that he considered difficult to solve. In particular, Monge explains how the descriptive geometrical procedure, involving the vision of the represented forms, allows you to exclude in a simple and direct manner the solutions that resolve the problem from theoretical point of view, but do not solve it in the real case because they lead to unrealistic placements of the projection center. Thus, the symbiosis between calculation and analog description, Monge had predicted in these words: «[…] la géométrie descriptive porteroit dans les opérations analytiques le plus compliquées l'évidence qui est son caractère, et, à son tour, l'analyse porteroit dans la géométrie la generalité qui lui est propre […]»

The Monge three point space resection problem / F., Fallavollita; Migliari, Riccardo; Salvatore, Marta. - STAMPA. - (2014), pp. 809-819. (Intervento presentato al convegno 16th International Conference on Geometry and Graphics tenutosi a Innsbruck nel 4-8 agosto 2014).

### The Monge three point space resection problem

#### Abstract

The study illustrates the solution of the three point space resection problem, treated by Gaspard Monge in Section V of Leçons de Geometrie Descriptive. The problem entails the construction of the intersection curves of three tori. To solve this problem, Monge introduces several simplifications but, nevertheless, makes a mistake; this mistake has already been pointed out by Gino Loria regarding the number of solutions allowed by the problem. The mathematical representation, thanks to its high level of accuracy, today permits not only an efficacious solution of the general case, it also highlights without difficulty the right number of solutions. We applied this theory to a case of photogrammetric rendering, difficult to carry out by means of the tools offered by commercial software. Case in question concerns the reconstruction of the architectural volumes, now lost, which were located along the road that crosses a village, near Rome. As is known, the reconstruction of points in space from two images is possible if these images are projective and we have at least two projective orientated stars. The first image is a vintage photograph (1892), the second image is a surveyed plan of the masonry still present at the site. Therefore, one of the two projective stars is assimilated to a class of vertical straight lines. With regard to photography, the problem is articulated in two typical phases of photogrammetric processes: internal orientation and absolute orientation. For the absolute orientation we used the pyramid vertex method, in use since the Eighteenth Century, which consists in determining the projection center from three given points of which the positions in space are known. The solution to the problem posed by the case study can be considered as a useful result. More interesting, however, is the result of the intersection of the three tori with the incident axes. It is, in fact, a graphic process that Gaspard Monge had already proposed in 1798 as a suitable alternative to a system of equations that he considered difficult to solve. In particular, Monge explains how the descriptive geometrical procedure, involving the vision of the represented forms, allows you to exclude in a simple and direct manner the solutions that resolve the problem from theoretical point of view, but do not solve it in the real case because they lead to unrealistic placements of the projection center. Thus, the symbiosis between calculation and analog description, Monge had predicted in these words: «[…] la géométrie descriptive porteroit dans les opérations analytiques le plus compliquées l'évidence qui est son caractère, et, à son tour, l'analyse porteroit dans la géométrie la generalité qui lui est propre […]»
##### Scheda breve Scheda completa
2014
16th International Conference on Geometry and Graphics
Descriptive geometry; three point resection problem; Gaspard Monge; photogrammetry
04 Pubblicazione in atti di convegno::04b Atto di convegno in volume
The Monge three point space resection problem / F., Fallavollita; Migliari, Riccardo; Salvatore, Marta. - STAMPA. - (2014), pp. 809-819. (Intervento presentato al convegno 16th International Conference on Geometry and Graphics tenutosi a Innsbruck nel 4-8 agosto 2014).
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Utilizza questo identificativo per citare o creare un link a questo documento: `https://hdl.handle.net/11573/607985`