Is The Earth A Flat Round Disc or Is It a Round Spherical Globe?

[TinselKoala]

Yes, but that's different because these green  tracks go off into the distance along the Z axis of the camera's vision.
The perspective distortion would not be able to distort the parallelness of e.g. these black poles planted along the tracks (because these poles are parallel to the Y axis of the camera's vision).

The sunrays in that image were not along the Z axis so they could not have been affected by the perspective distortion like the tracks.

Not at all. You can find many photos of tall buildings that appear to lean "inwards" toward the top. Also, architects know about this vertical perspective situation as well. For example the minarets of the Taj Mahal are actually built with a slight outward lean so that they appear vertical when viewed from the main gate.

https://dilemmaxdotnet.files.wordpress.com/2013/06/cayan-tower2.jpg

Many photos of city skylines can be found that show this perspective tilt, and many others can be found that do not, either because it has been corrected in processing or a particular angle has been used. Also remember that even the tallest buildings aren't nearly as high as the normal cloudbase on a fine fairweather cumulus day.

Not only that... but your black poles next to the railroad tracks look like they are getting shorter the farther away they are. Do you think this is real, or is it a result of perspective acting in the y-direction?

[TinselKoala]

one youtube doubled up. Laser youtube never made it.
Here it is:
https://www.youtube.com/watch?v=GBhDFO4NMrw

That's pretty silly. It has been known for a long time that the air over bodies of water can refract light beams, so objects that are actually "below" the horizon can _appear_ to be above it. It's a well-known cause of "mirages".  This is because of the dependence of refractive index of air on temperature differences in various layers of air-- the same thing that makes stars "twinkle" and appear to move around a bit at night.  Unfortunately -- for you and other flat-earthers -- this laser test is invalid for that reason.

[conradelektro]

Eratosthenes did it more than 2000 years ago:

https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_the_Earth.27s_circumference

http://www.dummies.com/education/math/geometry/how-to-determine-the-earths-circumference/

Other very old measurements:

https://www.britannica.com/topic/Measuring-the-Earth-Classical-and-Arabic-1673315

https://en.wikipedia.org/wiki/History_of_geodesy

But of course, they were all wrong, the earth is flat, just look out of your window.

Give a tool like a laser into the hands of silly people and you will get silly results and damaged retinas. Watching these people on lake Balaton disregarding the dangers of a laser (it could easily damage your retina in the eye) raised my hair. So, please do not use lasers like an idiot, stick to the ancient measurement methods, they are straight forward.

Simple test of flatness:

Put a stick into the earth on two different locations a few hundred miles apart as vertical as you manage. And then place a person next to each stick with a cell phone. Establish a call and compare the shadow of the sticks. It works best around mid day.

Of course you should know that the sun is very far (millions of miles) away (and not close to the earth surface as some flat people want you to believe).

I know, this has all been said here before, but some people just do not understand reality.

I like this old method:

https://en.wikipedia.org/wiki/History_of_geodesy#Al-Biruni

You only have to measure an angle on the top of a mountain (dip angle towards the plain around the mountain, could be a mountain near a lake or the sea)  and you have to know the height of the mountain relative to the plain. Even if you only know the height of the mountain approximately (50 meter accuracy, a map will tell you) it will show that the earth has to be a sphere and not flat.

If the mountain is 500 meters high (above the plain, lake or sea you use as a reference for the drop angle) the drop angle is about 0.7 degrees. So, you need a good surveying instrument (https://en.wikipedia.org/wiki/Theodolite, minute resolution).

This theodolite should do http://www.u-t-b.at/at/vermessungsgeraete/theodolite/mechanische-theodolite/geofennel-fet-500.html#.V9F24q04r9A , resolution 0.1 gon (about 0.1°) if you only want to proof that the earth is a sphere. The calculated radius will be between 4000 and 10000 kilometres, which is well beyond flat.

Greetings, Conrad

[verpies]

Not only that... but your black poles next to the railroad tracks look like they are getting shorter the farther away they are. Do you think this is real, or is it a result of perspective acting in the y-direction?

I think the black poles are getting visually shorter in the y-direction, because of the perspective effect.

[verpies]

That's pretty silly. It has been known for a long time that the air over bodies of water can refract light beams, so objects that are actually "below" the horizon can _appear_ to be above it. It's a well-known cause of "mirages".  This is because of the dependence of refractive index of air on temperature differences in various layers of air-- the same thing that makes stars "twinkle" and appear to move around a bit at night.  Unfortunately -- for you and other flat-earthers -- this laser test is invalid for that reason.

I have to agree with that.  Any long-distance optical observations in the atmosphere are not trustworthy because the atmosphere is a giant convex lens and the density gradients over water make atmospheric ducting even worse.
I was always curious what its average focal length is, ...as viewed from outside of the atmosphere.

So all of the long-distance visual evidence can be thrown into a proverbial "garbage", regardless whether it supports flat-Earth or curved-Earth.

An optical experiment that conclusively measures the curvature of the Earth would have to be arranged like this: