CathInfo.com

Below is the basis for the argument. Seems pretty sound to me. Don't be troubled. Explain how this is mischaracterizing the optical phenomenon. Again, I don't care too much but let me know how I'm being duped by this article. Don't really want to argue. Unlike my enemies in this subforum, I'm not dogmatic about this so I'm not using too much brain power on it.


The Vanishing Point
The vanishing point of an object is when the object is so far away from you it seems to disappear. Objects will disappear at different distances from you depending upon their size, your vision, and potentially atmospheric conditions. But the smaller the object, the closer to you it will reach it's vanishing point, and the contrary is true as well; the larger an object, the further away from you it will seem to vanish.

Versus over the Horizon
...When you get a large object, such as the container ship in the video below, you'll see that part or all of the ship is obscured by the horizon before it reaches it's vanishing point. The portion obscured by the horizon, it can be easily seen, cannot be zoomed back in with the zoom lens, and the rest of the boat is obviously visible, so it is clearly not an issue of the bottom being too small to see. It's simply obscured by the curvature of the earth!
...
In this case, many have realized that these objects simply cannot be brought back with a telescope, so they now claim that objects disappearing by 'perspective' just disappear bottom first, when it's clear to anyone who has watched small objects disappear into the distance, like these batteries on colored paper prove, this is simply not true. We can still see the furthest away colored paper on the floor, just as we'd expect to see.

.
This reference to "the vanishing point" is slightly off the mark strictly speaking. 
But it's well intended, perhaps an attempt to keep the description simple.
.
The vanishing point of an object has the SIDE EFFECT of it seeming to disappear. But that isn't the essence of what constitutes the vanishing point.
.
In simple perspective, a straight row of same-sized objects gets smaller in the distance, when the lines of their extremities converge, and it is this convergence of the lines of perspective when merging into one point that is the vanishing point.
.
Applying this to the horizon, flat-earthers are wont to confuse a level line of sight with the horizon.
.
Without any sure means to establish where the level line of sight goes as it approaches the horizon, it's far too easy to presume that they are one and the same, thus their erroneous claim that the horizon "rises to eye level," when in fact the horizon doesn't rise anywhere, nor does it fall. The horizon stays right where it is.
.
Rather it is the eye of the viewer without any device or guide to indicate where level is, that drifts down to meet the horizon, and so it is the eye that descends to the horizon and not the horizon rising to eye level.
.
Some of the links that I posted above demonstrate this, the first of which does so very well using mathematics, where the formula used by flat-earthers is derived and the consequences of mistaken application are described in detail by the derivation of the formula.
.
Walter Bislin's blog - http://walter.bislins.ch/bloge/index.asp?blog=list&tag=FlatEarth
.
Walter Bislin apparently speaks primarily German so that might explain why he spells "blog" as "bloge."
.
But his mathematical derivation is very impressive. There is no higher math there, just algebra and Euclidean geometry. 
.
Other forums have pointed out that flat-earthers in the past 6 months have backed away from claiming "perspective" as the explanation of why objects such as large ships recede downward over the horizon with the hull disappearing first, then the deck line, and finally the superstructure as they move further away from the viewer.
.
There are numerous diagrams available online that demonstrate why perspective is no good for explaining away this effect of earth's curvature.
.

.
Take a row of telephone poles or electrical power towers as an example.
.
Presuming that they are lined up on a flat plane, it would be true that a level line of sight somewhere near their bottom (such poles are a lot taller than the man standing next to them) would merge along with the perspective lines of the poles (or towers) to become one at the vanishing point in the distance.
.
But it is a mistake to superimpose this presumption onto an unknown situation, in an attempt to "prove" there is no curvature on the earth.
.
If the curvature is not known, nor is the levelness of the plane known, a level-finding instrument is required to determine where the level line of sight is. 
.
Consider the row of poles (or towers) could be on an inclined pane, either rising or falling in the distance. If the plane is flat but inclined upwards as it proceeds away from you, your line of sight could merge at the vanishing point all right, but it would be an INCLINED line of sight, since you have no reliable device to inform you otherwise.
.
Similarly, if the row of poles (or towers) recedes downhill in the distance, your line of sight would also recede along with them, and you would be unable to say with certainty whether the horizon line where the vanishing point is, is at the same level as your eye observing it.
.
Anyone with surveying experience knows this intuitively, since working with a dumpy level or theodolite gives innumerable situations where there is utterly no way to know where "level" is on a Philadelphia rod unless you have an instrument to look through and it is calibrated, adjusted, and verified for shooting a level line. Calibration is done in the factory. Adjustment is done in the field and verification is simply a process of leveling the instrument and reversing it 180 degrees to see that the gauges indicating level read the same way in both directions. A verified instrument reads "0" in all directions, and this must be done before any readings are taken.
.

.
Your emotionally charged outbursts discredit everything you say, Ladislaus.

While I certainly get irritated about various theological subjects, when errors are being promoted, I have been decidedly UNemotional about this particular issue.  You're the one who constantly goes into 10-paragraph emotional jags and insults and mockery.  And the evidence you have posted so far (once I have found it having had to wade through your posts) is mostly unconvincing.  I have not had the time to study some of the mathematical things you've posted, but you keep posting the visual stuff about the bottoms of ships disappearing at a distance, and that's not convincing to me.