Ludovico Cardi said "il Cigoli". Practical treaty of perspective: innovative aspects and intuitions.

The practical treatise of perspective (1628) is undoubtedly one of the less studied treatise, although there are some innovative aspects that are much earlier than the actual coding of perspective science. Filippo Camerota published and commented the Cigoli's treatise in his “Linear Perspective in the age of Galileo. Ludovico Cigoli's Prospettiva Pratica” and filled an empty space concerning Cigoli's contribution to the development of perspective. Camerota has highlighted many innovative aspects of the treaty, the profound knowledge of the perspective science of the treatise expressed in the first two rules, and confirmed by the third rule that, through the analysis, study and construction of a perspective machine, has allowed to confirm and endorse the first two. Already in other treatises we find the use, as an aid to the drawing, of some particular points, and even Albrecht Dürer himself uses the points of distance, without however having a full awareness of them and of the "punctum concursum". Cigoli was perfectly aware of the significance of these points and of the points of distance that he uses in an innovative way compared to the time. In the first case study, analyzed by reinterpreting the Cigoli text, the first conditions described by the author for the realization of a duly graduated theater scene were analyzed with a three-dimensional model. Through the comparison between the perspective representation of a stage with real dimensions and the reduced one, it is noted that traces and "punctum concursum" of the respective lines that divide the stage are inverted: in the first case the vanishing point is unique and in O0 (main point), while the traces they are on the geometrical trace, according to the distances indicated by Cigoli; in the duly graduated scene, there is only one trace right in O0, but as many "punctum concursum" as the lines that divide the stage (plane α), on the vanishing line (f'β) of an inclined plane β and parallel to the stage itself. In practice, with this configuration, the representation on the picture plane of one or the other lines is absolutely coincident. Unexpected is the use of the point of distance in the reduced scene: Cigoli uses it to subdivide the stage, in its depth, into portions apparently equal to the observer's eye. Also in this case the real line has a trace on the horizon and "punctum concursum" on the vanishing line of the β plane and belongs to the scenic plane, whose deduction of belonging is not really intuitive, having an angle of inclination different from the maximum slope of the α plane. Even more, the use of that line, and the derivatives by intersection with the edge lines of the stage, for the division into apparent squares, reveals a deep and conscious knowledge of Cigoli. The subsequent outline of the treaty show the use of distance and concourse points for the realization of the whole scene, even in elevation, whose reconstruction I hope will conceal new and further spatial analysis. The importance of Cigoli's precepts is explained by the ability he has, through only the first two rules, to create highly complex perspective illusions, also in reference to set designs and solid perspectives with the help of refined systems to project shadows too.