Those drawings are simplified. The only reason that the "new" definition of the minute of latitude being arc disance subtended by one minute from the center of curvature is that satellite mapping has made it possible to accurately map the real Earth Surface. For surface navigation, one common center of the Earth is possible. Few folks navigating are at the S or N pole, and those who do use GPS.
Hello again Bob, Thanks for your reply. The point that has grabbed my attention now is you refer to the "NEW" definition of the minute of latitude. Things are slowly falling into place at this end. Do you happen to know when the "NEW" definition of latitude was introduced?
It couln't be done until we knew the shape of the Earth with some precision, in particular the semimajor and semiminor axis. WGS 84 is the system that defined these lengths with some precision. With that, the point of curvature could be determined, and thence the distance subtended.
By the way, the international standard for a nautical mile is fixed as the average distance. All this is somewhat like mom's favorite apple pie recipe, it depends on who is eating, when, and what ingredients were available at cooking.
Hello Bob, love your analogy about mom's apple pie recipe.
Allow me to enter the NM debate at this point.
Do you happen to have a good explanation re the origin of the k in knots for "nautical miles per hour"?
This is as I learned it many years ago as a seaman.
That makes sense.
BTW, interesting thread.