Years ago, reading the book of Andrè Pochan The enigm de la grand piramid, I've read about the irregular unflatting of the side faces. Each face is really consisting of two, then each face is concave, with a little indentation of about 1 meter (evaluation of the author).
I've not read nothing more about this characteristic.
Seeing a beautiful photo of the Giza pyramids from the sky, I see that this strange construction there is in Cheops and in menkaura pyramid, but not in Kephren pyramids that exhibits flat faces.
Andrè Pochan speaks only of Cheops pyramid.
Can someone give to me more references where can I read about it?
thanks

The reason you haven't found any further references to this phenomenon is that it isn't true. Look carefully at the photo you posted & you'll notice that the apparent curvature of the base & sides is a combination of sand having piled up around the pyramid base & an optical illusion created by the, not quite, vertical angle at which the photo was taken (enhanced by the effects of light & shadow in a black & white photo).

Not surprising that the author only speaks of Khufu's pyramid, as it has attracted more baseless theories than just about any other structure on earth, none of which has any basis in the realities of either the monument itself or the site of Giza.

Sorry to disappoint you.

Glen

Thanks for your answer.
It may be so, but look this photos for Cheops and Kephen pyramids (parts of the big original) and note the difference.
Let me know.
Greatings
Giuseppe

This photo (below), at least to my eye, doesn't appear to show the same anomaly that you describe. However, lens aberrations can certainly account for and probably do contribute to this myth. The only real way to get the precise angles is with surveying equipment, take precise measurements and calculate the angles and deviations. This is exactly what was done in the 1880s by William Matthew Flinders Petrie. His work has become the defacto standard of Giza surveys. More recently, Jean-Pierre Houdin modeled the Great Pyramid to test various construction theories. As far as I know, neither of these scholarly works describe such anomalies.

Quote from Peter Tompkins’ “Secrets of the Great Pyramid”:
Sir Flinders Petrie noted a distinct hollowing of the core masonry in the central portion of each face of the Pyramid. Though the hollowing amounts to as much as 37 inches on the north face, it is not directly observable unless special lines of sight are taken. Petrie found no evidence of hollowing along the lower-level casing stones, running along the base of the Pyramid, which have now been completely uncovered.
A recent survey by two Italian scholars, Maragioglio and Rinaldi, indicates the casing stones above the base line may have been slightly sloped toward a central line.


There is no doubt that the faces of the Great Pyramid are concave. André Pochan only noted the flash phenomenon.
The fact that the angle of hollowing approximately equals the diameter of the sun and moon, probably indicates a method devised to signal the exact moment that the center of the sun was located on the plane of the Pyramid’s side.

Nothing of the sort. Any hollowing of the faces of the Great Pyramid are due to the efforts of stone robbers & do not reflect the original appearance of the monument.

Petrie's observation, "Petrie found no evidence of hollowing along the lower-level casing stones, running along the base of the Pyramid, which have now been completely uncovered." which you cite in your quote from Tomkins demonstrates this.

There are some other theories here (but they aren't technically supported, in my modest opinion it could only help imagination: until they don't prove what they say, I won't believe it).