[AATW]

I have not seen evidence that Web Mercator (Web-based WGS84 used in Google/Bing Maps) is based on a sphere. Various statements suggest otherwise -  https://wiki.tfes.org/World_Geodetic_System_1984

Literally the second sentence:

"WGS84 represents the world with a spherical coordinate system"

What are you looking at?

[Tom Bishop]

I have not seen evidence that Web Mercator (Web-based WGS84 used in Google/Bing Maps) is based on a sphere. Various statements suggest otherwise -  https://wiki.tfes.org/World_Geodetic_System_1984

Literally the second sentence:

"WGS84 represents the world with a spherical coordinate system"

What are you looking at?

Keep reading:

"When assessing this claim it is found that the process is a complex system which pulls information from a large collection of smaller flat maps to provide information to users.[1] The measurement and coordinate information is temporarily reprojected and retrieved from flat maps with planar coordinates in order to provide accurate geospatial data.[2] The Latitude and Longitude coordinate system is described as unreliable and is not used to measure distances or area.[3]"

[Tumeni]

I have not seen evidence that Web Mercator (Web-based WGS84 used in Google/Bing Maps) is based on a sphere. Various statements suggest otherwise -  https://wiki.tfes.org/World_Geodetic_System_1984

Citing a document which you or your associates wrote is hardly citation of a valid source of evidence. The fact that YOU have not seen some evidence is not, of itself, a proof that the evidence does not exist...

WtF is "temporal reprojection"? EDIT - Tom has corrected the grammar "This page was last modified on 31 July 2020, at 07:56."

Further EDIT as Tom was replying, leading to crossed posts;

Your quoted [1] cherry-picks its quote. The AGRC specifically says that users of the GIS need to know three co-ordinate systems, and you quote only one of the three. The first says;

"Geographic coordinates use latitude and longitude values to define positions on the 3D surface of the earth, which is of course, best modeled as an ellipsoid, not a sphere. The ellipsoid and its accompanying anchor point that ties it in to the real world, are known collectively as the WGS84 datum. The WGS84 datum is what the constellations of GPS satellites use natively."

[Tom Bishop]

Citing a document which you or your associates wrote is hardly citation of a valid source of evidence. The fact that YOU have not seen some evidence is not, of itself, a proof that the evidence does not exist...

I didn't make the sources referenced. Those are conventional mainstream sources who say that the information comes from flat maps. The Wiki is largely a collection of mainstream sources with minimal commentary.

Your quoted [1] cherry-picks its quote. The AGRC specifically says that users of the GIS need to know three co-ordinate systems, and you quote only one of the three. The first says;

"Geographic coordinates use latitude and longitude values to define positions on the 3D surface of the earth, which is of course, best modeled as an ellipsoid, not a sphere. The ellipsoid and its accompanying anchor point that ties it in to the real world, are known collectively as the WGS84 datum. The WGS84 datum is what the constellations of GPS satellites use natively."

And that article goes on to explain that the geographic coordinate system retrieves information from a flat coordinate system. Hence the title "The Earth is Not Round!"

[Tumeni]

Your quoted [2] also cherry-picks, missing out the earlier description;

"UTM NAD83 is a projected coordinate system that represents physical locations abstracted to a flat, cartesian coordinate system. The UTM NAD83 projection uses the GRS80 ellipsoid and a center-of-the-earth anchor point as its datum, both of which are slightly different than the WGS datum. The advantage of the NAD83 datum is more accuracy for modeling and analyzing locational data in North America. As almost all of Utah fits conveniently within one UTM NAD83 zone (12 North), it’s the best projection system for measuring distance and area when working with statewide GIS data."

If you have to "abstract" the physical location in order to represent it in a flat, cartesian coordinate system, does that not suggest to you the absence of flatness in the physical location? Else why would you need to abstract it?

This datum is stated to be used because of the small size of the area considered, and its accuracy for this specific state, in its specific location. There is no suggestion this extends to other states, nor other countries.

[Tumeni]

Tom, why do you think the article includes an exclamation mark after the phrase "The Earth is Not Round"

?

EDIT; [3] expresses that the "WGS84's significant weakness is that measurements of distance and area in its native coordinates are completely unusable."

but this is in the context of usage of their GIS system, there's no suggestion that this applies universally, either in other states or other countries. Note also the emphasis on "native coordinates" as a specific rider.

You also cherry-pick here, ignoring the previous paragraph;

"Web Mercator is relevant for 2 reasons and both reasons are related to basic, map display functions. First, it is great for maps of large areas, where more than the state of Utah may be needed. Second, it has become, and will likely remain for some time, the de facto coordinate system standard for web mapping applications, because, as mentioned above, it works well for maps depicting the portions of the globe we care about most, and because it performs coordinate conversion faster."

For an article which you claim has the title (excluding exclamation mark) "Earth is Not Round", they sure do seem to accept the globe quite a bit ...

 

 

[Tom Bishop]

Incorrect. The anchor point datum ties the projected coordinate system (flat) and the geographic coordinate system (round) together. The round system takes data from the flat system.

Tom, why do you think the article includes an exclamation mark after the phrase "The Earth is Not Round"

Because it is expressing that these are not systems based on a round earth.

[Tumeni]

Incorrect. The anchor point datum ties the projected coordinate system (flat) and the geographic coordinate system (round) together. The round system takes data from the flat system.

Tom, why do you think the article includes an exclamation mark after the phrase "The Earth is Not Round"

Because it is expressing that these are not systems based on a round earth.

The anchor point is specifically expressed as a "Centre of the Earth" anchor point. The Earth can only have a centre if .... Oh, go on, you know how this sentence ends, don't you?

The systems are stated as "physical locations abstracted to a flat, cartesian coordinate system"

If the Earth were not round, there would be no need to abstract them, would there?

[Tom Bishop]

There are three things here: The round earth (geographic system), the flat maps (NAD84), and the anchor point datum ellipsoid that connects the systems together.
The anchor point datum "center of earth" connects to the geographic (round) system's "center of earth". It is necessary to connect the two systems together.

"abstracted" just means the data is put on a plane

[Tumeni]

"abstracted" just means the data is put on a plane

Why would you need to do this, were the Earth already flat?

What abstraction is needed to put the data from a flat, plane Earth onto another plane? None, surely?

There are three things here: The round earth (geographic system), the flat maps (NAD84), and the anchor point datum ellipsoid that connects the systems together.

Except the page you quoted explicitly states that the geographic and NAD84 anchor points are slightly different. Two anchor points, one for each system, so no connection between

[Tom Bishop]

"abstracted" just means the data is put on a plane

Why would you need to do this, were the Earth already flat?

What abstraction is needed to put the data from a flat, plane Earth onto another plane? None, surely?

What? The data needs to go onto some shape. The author is explaining that the NAD84 puts the data onto a plane.

If the maps were round one could say that the data is abstracted onto a curved surface. It would mean that the data is put onto a curved surface.

The maps are flat because surveyors and mappers use plane surveying techniques.

Except the page you quoted explicitly states that the geographic and NAD84 anchor points are slightly different. Two anchor points, one for each system, so no connection between

It specifically says that the systems work together and the data is re-projected from round earth to flat earth in order to be usable and gather accurate distances and area calculations:

"Web Mercator’s significant weakness is that measurements of distance and area in its native coordinates are completely unusable. Where accurate distance and area calculations are needed, web-mercator GIS data must be temporarily reprojected to a more suitable coordinate system (UTM NAD83)."

[robinofloxley]

Well I don't consider the earth itself to have an interactive surface with a scale that changes as you move across it, so I don't particularly care that Bing has an interactive scale.

But it is. When you see something very far away that is very small your brain knows that, because that small thing is very far away, the scale of the item is large. When I see the mountains, which are just a few inches tall off on the horizon my brain passively understands. When I look out the airplane window at 30,000 feet I know the scale of the surface of the earth has changed and, what was a very small distance, from the airplane is a much larger distance from the surface of the earth. If I took a picture from the airplane and drew a scale on it that scale would be much different than the scale from a picture taken at ground level.

Well I find that a very odd definition of an interactive scale. Using that logic I can look at a wall map and take a step backwards and say the scale has changed. OK, so on that basis, I'll say map 2 has an interactive scale because it looks smaller from 2 metres away on my screen than 1 metre.

If anything, that makes me less likely to think it represents any kind of reality.

I just gave an example of how, in the real world, a video of the surface of the earth should have an interactive scale.

Secondly, where exactly is the south pole on a Bing map?

It's not a single point, it's a horizontal line that stretches all the way along the base of the map whether you are zoomed in or not.

That's funny because I didn't see a line. I saw an area of land on Antarctica when i search for south pole on bing.

Well in my book, the (geographic) south pole is a physical point on the earth I could visit and stick a pin in, located at latitude 90S.

Try zooming in or out as much as you like on Bing maps, locate the furthest south point you can, right click (for a Windows user) and it shows you the position you clicked in latitude/longitude coordinates. You'll find the furthest south you can get is -85 or 85S. Similarly, the furthest north you can go is 85N. Basically Bing is not showing you the last 5 degrees at the top or bottom. That's 69 miles of the earth you are not seeing at each pole. You don't even have a north or south pole on your Bing map. At least map 2 shows the north pole correctly.

The reason you can't go all the way to 90° is that mathematically it would blow up because you end up with an infinitesimally small point at the exact geographic pole where all the longitude lines converge. I'm surprised that they actually ditch a whole 5°, but I guess that makes things easier to compute.

That's no more realistic to me than the rim of the circle on model 2. At least with map 2 I can put a pin in the exact location of the north pole. Map 2 doesn't say anything about there being a wall, it's a flat 2D surface. Sure, many FErs add the ice wall part, but that's not something you can deduce just from looking at the map.

If you search for south pole Antarctica on Bing you don't see a map. Even if you did see a line that would not change the fact that one model has a south pole and no ice barrier perimeter and one does.

Also, I don't consider 1&2 to be different models at all, just different presentations of the same information.

You are seriously arguing semantics about the word "model". Fine then. What "presentation style" do you believe most closely depicts the planet that you live on.

"presentation style" 1:

-depicts the earth as a defined area with a defined edge
-depicts the earth as having a great ice wall around this perimeter edge
-depicts the earth as not having a south pole
-not supported by know travel paths/times
-not taught in schools all over the world as a "presentation style" of the surface of the earth


"presentation style" 2
-depicts the earth as an interactive surface with no defined edge
-depicts the earth as not having a great ice wall (partly because there is no perimeter edge)
-depict the earth has having a south pole
-supported by know travel paths/times
-taught in schools all over the world as a "presentation style" of the surface of the earth

So style 2 doesn't show north or south pole, since it misses out parts of the earth. What is the north and south boundary of the map, beyond which you cannot go? Looks like an edge to me. The southern boundary is entirely white. Is this not an ice wall? How is this different from the white edge of style 2? Why do you say one area of white is an ice wall and the other area is not?

Actually a number of schools are no longer teaching using Mercator (https://www.theguardian.com/education/2017/mar/19/boston-public-schools-world-map-mercator-peters-projection) because they want to offer "something closer to the geographical truth than that of traditional school maps". It is acknowledged that Mercator portrays Europe and the USA as bigger (and by implication more important) than they actually are in relation to regions such as Africa and South America. Basically it's an old fashioned view of the world and gives children the wrong idea. In all probability, the majority of schools still use Mercator, but it's changing as people become more aware.

Both models are accurate in some respects and inaccurate in others. Model 1 is good around the equator and poor around the poles. Model 2 is good around the north pole, poor around the equator and poor around the south pole. How am I supposed to come to any kind of conclusion about which model is better than the other?

I thought you just said they were not models? Now you are saying they are models. The Bing map "presentation style" has an interactive scale which makes it much more accurate both around the poles and around the equators

In the very next sentence I use the term "model/projection" for extra clarity because you use the term model for what I would describe as a projection. To me, you can't view a model. The model is mathematics and data. Viewing a 3D globe on a 2D screen is an orthographic projection. You are looking at the projection, not the model. In my view, there is one model, based on a spherical earth and many projections of that model. Pseudo 3D on a 2D screen (i.e. Google 3D zoomed out) is one, "models" (your usage) 1 & 2 are others. I term these projections, you say model, that's fine, I apologise, my wording was careless.

I can use some GIS software to zoom in as much as I want to on a particular area of a map using either model/projection and I can use haversine to calculate distances on either model (and they will agree with each other). I know this isn't instant and interactive, but who cares? I certainly don't.

Can you show me, online, where anyone has made an interactive map out of the flat disk, great ice wall, "presentation style" of the surface of the earth

I'd be very surprised if such a thing exists, why would anybody bother? But if you want to show me a screenshot of a zoomed in area on Bing maps with a scale, I'll gladly have a go with some GIS software and reproduce it for you using the "model" 2 north polar azimuthal equidistant projection.

[edby]

I have not seen evidence that Web Mercator (Web-based WGS84 used in Google/Bing Maps) is based on a sphere. Various statements suggest otherwise -  https://wiki.tfes.org/World_Geodetic_System_1984

From the 'Earth is not Round' article quoted: "Latitude and Longitude are useless for measuring distance and area because the unit of length, degrees, is not held constant for longitude, except along parallels -- individual perfectly east-west lines."

Well of course. Latitude and longitude are measures of location, not position. Points on a flat earth would have the same latitude and longitude as on a spherical earth.

The topic here is whether (1) the observations of flight time are a good proxy for flight distance, and (2) whether the distances inferred tell us anything about the shape of the earth.

The maps are flat because surveyors and mappers use plane surveying techniques.

"Geodetic Surveying is that branch of survey which deals with areas so extensive that it is necessary to take into consideration the true shape and dimensions of the earth". https://www.tandfonline.com/doi/abs/10.1080/00050326.1935.10436447

In plane surveying, used for small areas, the shape of the earth is not a consideration because it makes very little difference.

Wikipedia: "Plane and geodetic surveying: Based on the considerations and true shape of the earth, surveying is broadly classified into two types.Plane surveying assumes the earth is flat. Curvature and spheroidal shape of the earth is neglected. In this type of surveying all triangles formed by joining survey lines are considered as plane triangles. It is employed for small survey works where errors due to the earth's shape are too small to matter.In geodetic surveying the curvature of the earth is taken into account while calculating reduced levels, angles, bearings and distances. This type of surveying is usually employed for large survey works. Survey works up to 100 square miles (260 square kilometers ) are treated as plane and beyond that are treated as geodetic. In geodetic surveying necessary corrections are applied to reduced levels, bearings and other observations."
https://en.wikipedia.org/wiki/Surveying#Plane_and_geodetic_surveying

[AATW]

I have not seen evidence that Web Mercator (Web-based WGS84 used in Google/Bing Maps) is based on a sphere. Various statements suggest otherwise -  https://wiki.tfes.org/World_Geodetic_System_1984

Literally the second sentence:

"WGS84 represents the world with a spherical coordinate system"

What are you looking at?

Keep reading:

"When assessing this claim it is found that the process is a complex system which pulls information from a large collection of smaller flat maps to provide information to users.[1] The measurement and coordinate information is temporarily reprojected and retrieved from flat maps with planar coordinates in order to provide accurate geospatial data.[2] The Latitude and Longitude coordinate system is described as unreliable and is not used to measure distances or area.[3]"

Right. To be honest, I'd missed that the page you referenced was from your own Wiki.
So you're backing up your own argument with your own argument? Compelling...
So are cartographers in on the conspiracy then? Pretending they're mapping a globe earth when they're not really?

[Tumeni]

Well of course. Latitude and longitude are measures of location, not position. Points on a flat earth would have the same latitude and longitude as on a spherical earth.

Latitude and longitude have no meaning on a Flat Earth. They are measured in degrees of angle; angular displacement between two straight-line vectors which meet at a point, with the angle being at that point.

Where do you define this point on a Flat Earth?

[edby]

Latitude and longitude have no meaning on a Flat Earth. They are measured in degrees of angle; angular displacement between two straight-line vectors which meet at a point, with the angle being at that point.

Where do you define this point on a Flat Earth?

The coordinates are perfectly meaningful on a Flat Earth. We observe the altitude (in degrees) of polaris (or sigma octans) to find latitude, and the Greenwich time at which the sun is at its zenith (and multiply by 15) to find longitude. That gives us two coordinates, right?

[AATW]

Latitude and longitude have no meaning on a Flat Earth. They are measured in degrees of angle; angular displacement between two straight-line vectors which meet at a point, with the angle being at that point.

Where do you define this point on a Flat Earth?

The coordinates are perfectly meaningful on a Flat Earth. We observe the altitude (in degrees) of polaris (or sigma octans) to find latitude, and the Greenwich time at which the sun is at its zenith (and multiply by 15) to find longitude. That gives us two coordinates, right?

Right. But if that's how you're doing it you understand that degrees of latitude can only be a consistent distance apart using those observations if the earth is a globe? If it's flat then every degree south will get further and further apart.

[edby]

Right. But if that's how you're doing it you understand that degrees of latitude can only be a consistent distance apart using those observations if the earth is a globe? If it's flat then every degree south will get further and further apart.

Depends on the FE model you are using. On the AE map, I agree. There are other maps, according to the wiki.

[EDIT]Sorry, re-read your post. You are talking about distance between latitudes, yes? I agree.

[Tumeni]

The coordinates are perfectly meaningful on a Flat Earth. We observe the altitude (in degrees) of polaris (or sigma octans) to find latitude, and the Greenwich time at which the sun is at its zenith (and multiply by 15) to find longitude. That gives us two coordinates, right?

In the first case, you have not determined a "latitude", all you have done is observe the elevation of Polaris from your location. You're saying that represents or translates to a latitude, where the latitude is something independent of the elevation, but you have no definition for what it is.

If you say the latitude is 15 degrees, then you are specifying an angle. If that angle is not the one drawn between your horizontal and the sightline to Polaris, then what is it?

[Tumeni]

... and, to get back to flight-related stuff, today's flight BAW6B, arrival LHR 13:35 on Friday 31st, is currently over open ocean, South of Greenland.

Observed at 10:45am UK time (UTC+1)