quadibloc wrote:I am sorry that my posting was unclear.
Not to worry, because I think my posting was unclear, too!
Of course I got that you know that, my main point was that anybody who ever had a German school atlas in his hands (at least since the 1970ies) should know that there are other projections. But yes, of course it’s quite possible that you don’t pay attention in the geography lessons at school and still get a job at a popular science TV program.
Atarimaster wrote:But yes, of course it’s quite possible that you don’t pay attention in the geography lessons at school and still get a job at a popular science TV program.
The situation is worse than that. For my web page, I was looking for an illustration of the Azimuthal, Conical, and Cylindrical aspects of a projection. I thought this was so common I would be able to find it in a 19th-century book in the public domain, but after trying a few, it seemed like that was not the right direction to search.
So I figured I might find something in a U.S. government publication. Indeed I did find artwork I could use.
It was in Grids and Grid References, Department of the Army Technical Bulletin TM 5-241-1, dated June 1967.
However, in the artwork for the Cylindrical aspect, it was stated that the Mercator projection was a perspective cylindrical projection with the projection point 3/4 of the Earth's diameter below the ground. Unlike the more common misconception that it's projected from the Earth's center, this is actually a fairly good approximation... but nowhere in the text was it stated that it was an approximation.
So you can even have a job telling the country's soldiers how to read topographic maps, and not know that the Mercator is not a perspective projection.
EDIT: I may have been unfair. I went back to the text and checked more carefully, and I found "The origins of the projection lines are about three-quarters of the way back along the diameter"; this, of course, does not make it clear that the Mercator is not a perspective projection, as it could mean that the projection point has a distance of 0.7502 radii. However, since the fact that the poles are at infinity was also cited, requiring 0.5 radii, it might be possible for someone to eventually figure out that it couldn't be a perspective projection.
As I noted, I found this in the immediate vicinity of images which described the azimuthal, conic, and cylindrical aspects of projection. So it's easier to link points on the globe to points on the map if you use straight lines, literally "projected" from a point. I think that was the pedagogical aim. But seeing an apparent claim that the Mercator was a perspective projection in the immediate vicinity of a discussion of the ellipsoid and other advanced topics was indeed jarring.
I have now found a use for the three-quarters perspective projection,
Since it's a close imitation of the Mercator, although without the property of conformality, and it was easier to draw back in the days when computers weren't available, and since the Miller Cylindrical Projection, which is derived from the Mercator, doesn't have any particular properties either, why not apply the procedure used to obtain the Miller Cylindrical Projection from the Mercator to the three-quarters perspective cylindrical instead, and get a nice-looking conventional cylindrical projection that can be drawn by geometric pencil-and-paper means?
Although this is ever so slightly more compressed towards the poles, it's hard to tell from the real thing.
Last edited by quadibloc on Mon Apr 20, 2020 10:25 pm, edited 1 time in total.
Here's another example of someone being wrong, this time on the Internet.
A Google search on map projections led me to https://www.usna.edu/Users/oceano/pguth ... ctions.htm which displays illustrations of a number of map projections for the benefit of students at the U. S. Naval Academy. One of the example illustrations is wrong, though; the Miller Cylindrical projection is illustrated by a central perspective cylindrical projection. I couldn't find a link with which to notify the site administrator of the error.
