I agree that these are highly speculative books and that some would share your opinion. Though the many good reviews and endorsements would not agree with you. Strictly in regards to the question asked by HDE, for the evidence the Egyptians knew about the spherical earth, it is like math and physics. The mathematical calculations of the ancients on "earth measures" are very accurate and require space satellites to match them today. Are you refusing to acknowledge the mathematics and the physical reasoning behind it?
The speculative references make for challenging, controversial and interesting reading; on the leading edge of discovery and that's why they were posted. They also include the answer to HDE's question and more traditional references to the controversial nature of this question. Would it be fair to exclude controversial references in responding to a controversial question, especially when they seem to have the most accurate answers?
More conservative references show the "Pythagoreans were the first ... to say the earth is round." - George Sarton (noted founder of the academic discipline of the History of Science) Ancient Science Through the Golden Age of Greece. Pythagoras was an Egyptian initiate and some of his knowledge was directly attributed to the Egyptians. Both Kepler and Newton were also privy to some of the secret oral tradition. Kepler acknowledged his debt to the Egyptians. Newton went to great lengths in a paper trying to figure out the Sacred Cubit.
Another "source": Ancient Wisdom Discovery that the Earth is spherical -
The first (official) measurement of the radius of the earth was made
by Erasthenes (b. 275 B.C.), who was the head of the great library of
Alexandria. He was born in Cyrene, now Libya. It seems likely that the
ancient Egyptians, much before Egypt's conquest by Alexander the
great, had already grasped the idea of a spherical Earth, and it was
from them that this doctrine was adopted by Pythagoras, who, as we
know, spent many years of study in Egypt.
Another conservative reference, authoritative, with additional considerations:
Corinna Rossi, Architecture and Mathematics in Ancient Egypt, Cambridge University Press, 2004.
OK ... a little math :-) ... The approximate diameter of the earth in miles: 7920 = 8 x 9 x 10 x 11. These numbers are encoded in the geometry of the Cosmological Circle. Michael Schneider, Constructing the Cosmological Circle:
The Cosmological Circle is a geometric diagram that has appeared in
the arts, crafts, architecture, religion and literature of cultures
around the world, and is associated with their golden ages. Because
it's the visual representation of the harmony naturally inherent in
the structure of the numbers 1 through 12, it encodes the ideal
patterns and proportions toward which nature's forms strive. ... Its
dimensions are described as the Heavenly City described in The Book of
Revelation, seen in the plan of the Buddhist Brobodur temple,
Stonehenge, Glastonbury, and described as Plato's ideal city Magnesia.
Also, 7920 = 55 x 144. Notice the Fibonacci numbers and that 144/55 is approximately equal to the Golden Number squared. Half the value of the the Golden Number squared is equal to the midradius of the dodecahedron. Schneider says the geometry is just a mask for the Number Canon. Now, the question is how did they discover the Number Canon?
The Number Canon removes the geometric mask and looks into the numbers
at the heart of the Cosmological Circle. The way the twelve numbers
combine and organize into an all-encompassing whole was the model for
most of the ancient world as a microcosmic representation of the
harmonious universe. It was used as a standard for defining
relationships among weights, measures, music and the proportions of
sacred art and architecture.
According to WolframAlpha, ... this answer requested by AnubhaV ... is mathematically correct.
Supporting references -- Thoth: Architect of the Universe, by Ralph Ellis, in a review by Elliot Malach he says:
The author ties the measurements and mathematics of the pyramids,
Stonehenge and Avebury with the myth of Thoth, who educated mankind in
math and the mysteries of the heavens, leaving repositories of
knowledge throughout the Earth. Those repositories may not be "inside"
these megalithic structures, but instead the fundamental mathematics
encoded in the architecture of these structures themselves.
From Wikipedia Thoth:
The Egyptians credited him as the author of all works of science,
religion, philosophy, and magic. The Greeks further declared him the
inventor of astronomy, astrology, the science of numbers, mathematics,
geometry, land surveying, medicine, botany, theology, civilized
government, the alphabet, reading, writing, and oratory. They further
claimed he was the true author of every work of every branch of
knowledge, human and divine.