Frans, You can answer your own question. Photograph a drawing of a vertical sundial and compare the drawing with the corrected photo.
Kind regards. Willy "Frans W. MAES" wrote: > Hi All, > > John Carmichael wrote: > > > But I discovered that by using digital editing, you can stretch or > > compress a photo so that it appears that camara was directly over the > > dial! I discovered this while using the "perspective" and "distort" > > features of Adobe Photo Delux. > > I sometimes apply the same trick, using Paint Shop Pro. Starting > with a picture of a rectangular dial face taken at an arbitrary angle, > this involves 4 steps: the horizontal and vertical perspective tools are > used to make the sides parallel, then the horizontal and vertical > skewing tools are used to make them parallel to the picture frame. > > My question, however, is: does this procedure guarantee to yield the > correct result? That is: is the resulting height/width ratio equal to that > of the original? If not, angles between hour lines would be distorted. > As a consequence, it would be impossible to check the correctness > of the hour line layout, or to calculate the latitude for which the dial > was designed. > > Kind regards, > Frans > > ===================================== > Frans W. Maes > Peize, The Netherlands > 53.1 N, 6.5 E > www.biol.rug.nl/maes/sundials/ > =====================================
