A video disputes the earth is a globe, claiming civil engineers and aircraft pilots never factor the planet’s curvature into their calculations.
This is false. Experts told AAP FactCheck the claim is ridiculous and the earth’s curvature is always taken into account – by engineers planning major projects and pilots when following the shortest route to a destination.
They say without using calculations to factor in the earth’s curve, infrastructure projects would fail and flights would take much longer.
The claim is made in a Facebook video (screenshot here), which originally appeared on TikTok. It’s a compilation of rants by US comedian Owen Benjamin on whether the earth is a spinning globe.
“Civil engineers do not use a globe model,” he says (video mark 4min 38sec).
“They never factor in curve at all. Aeroplane pilots use a flat earth map. They never factor in curve.”
Benjamin claims this shows the earth is not a globe.
AAP FactCheck put the claim to separate academics in the fields of surveying, engineering and aviation, with all saying there’s abundant evidence to the contrary.
Kevin McDougall, a surveying professor at the University of Southern Queensland, said civil engineers factor in earth curvature by using a benchmark called vertical datum – specific points with known heights either above or below mean sea level (MSL).
Professor McDougall said the Australian Height Datum (AHD) was used to ensure large-scale infrastructure – roads, bridges, tunnels and planned cities – were at consistent levels over distances and so things such as drainage systems worked.
Prof McDougall said without using AHD and “quite a bit of complex mathematics”, major projects would end in disaster.
“This ensures that when we design projects that need infrastructure they are related to AHD and then of course water naturally flows to MSL and also that other infrastructure such as sewers, water distribution networks and stormwater systems work as planned,” Prof McDougall said in an email.
“If this didn’t happen and we simply treated the earth as a simple plane tangential to the earth at a particular point then the curvature over 1km would be approx. 0.08, 1.96m over 5km and 196m over 50km.
“So basically our infrastructure would not work as designed if we used a flat plane.”
Calculations relating to curvature over distances are shown here.
Professor Ian Williamson, an expert on infrastructure engineering at the University of Melbourne, told AAP FactCheck the video’s claim was ridiculous.
“Of course civil engineers and land surveyors factor in the earth’s curvature (of course earth is an oblate spheroid or ellipsis that represents the mathematical equivalent of the geoid) where appropriate,” Prof Williamson said in an email.
However, he said small distances were considered “effectively flat for many purposes such as construction”.
On how pilots factor in earth’s curvature, Professor Cees Bil, from RMIT’s School of Engineering, told AAP FactCheck flights followed the great circle distance line “because a map is a 2D (two-dimensional) representation of a spherical globe”.
Great circles follow the shortest distance between two points on a globe – as opposed to a straight line on a 2D map – and are circles which circumnavigate the earth and pass through the earth’s centre.
In other words, a great circle divides the earth in two equal hemispheres, such as the Equator. Similarly, every line of longitude is a great circle.
As an example, Prof Bil referred to a typical flight route between London and San Francisco, which was not a straight line but a curve taking the aircraft to the tip of Greenland and northern Canada.
“Closer to home, a flight from Melbourne to Santiago de Chili goes south, not east,” Prof Bil said.
“It flies over Tasmania, west of New Zealand and past Antarctica.”
Professor Doug Drury, an aviation professor at Central Queensland University’s School of Engineering and Technology, also said flying was three-dimensional.
“It takes longer if you actually flew a straight line between two points,” Prof Drury told AAP FactCheck.
He said aircraft followed great circle routes to minimise flight times.
The Verdict
The claim civil engineers and pilots do not take the earth’s curvature into account is false.
Experts told AAP FactCheck the earth’s curve is factored into projects by using a benchmark called the vertical datum or Australian Height Datum.
Pilots rely on the curvature of the earth to fly the shortest distance between two points, which follows the great circle distance, not a straight line as represented on a two-dimensional map.
False – The claim is inaccurate.
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