Spheroids, Ellipsoid, and Geoid - GIS Fundamentals and Mapping (4)

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[@OoWINDEXoO]

Hi Heath, big fan! Quick question: At about 2:20, are you sure that you are not describing a MAJOR and MINOR axis as opposed to a SEMI-major and SEMI-minor axis? Hope that question makes sense, thanks!

[@GeoMindzcom]

This is an excellent question. I looked up some more information to make sure that I had the terminology right. And, it does seem that when I referred to the semi-major and semi-minor axis I should have just referred into the major and minor axis. I am sure I got that terminology from using the ArcGIS platform, and so according to them: "A spheroid is a three-dimensional shape created from a two-dimensional ellipse. The ellipse is an oval, with a major axis (the longer axis) and a minor axis (the shorter axis). If you rotate the ellipse, the shape of the rotated figure is the spheroid. The semimajor axis is half the length of the major axis. The semiminor axis is half the length of the minor axis. For the earth, the semimajor axis is the radius from the center of the earth to the equator, while the semiminor axis is the radius from the center of the earth to the pole." That is from - desktop.arcgis.com/en/arcmap/10.3/guide-books/map-projections/about-the-geoid-ellipsoid-spheroid-and-datum-and-h.htm It appears that the information that software package reports about the spheroids is the length of the semi-major and semi-minor axis. But, yes, very importantly, that is half the distance across the planet, and therefore something akin to the radius of a sphere (as opposed to its diameter). The whole distances are just the major axis and the minor axis. Thank you for the catch! That is great!

[@OoWINDEXoO]

GeoMindz.com Great answer! Thank you so much, Heath!

[@GeoMindzcom]

You are welcome! Anytime! :-)

[@peterheine6240]

Hello what is the difference between Geoidundulation and altitude anomaly.

[@johng5295]

Your course is second to none! It is very well structured, very well explained, and easy to follow. This is the second time that I am revisiting this course in full. Thanks in a million.!Great content. Awesome. Very well explained. I couldn't find this explanation--simply put anywhere else. "Great teachers are hard to find". Grade: A++💥

[@almuhaymin8439]

In Quran the term is da ha ha Which means ostrich egg. .. Referring to geoid shape of earth

[@angelopoupard10]

Thank you so much for describing in such a simple manner what I have been trying to understand for the last weeks :)

[@GeoMindzcom]

You are very welcome. I am very glad it helped!

[@busrabahcivanci]

Please continue your videos. As a Geoinformatics master student, it helped me a lot

[@Earthislife1031]

This is kryptonite to flat earthers

[@Earthislife1031]

@James Henry Smith yea....only...its not

[@Earthislife1031]

@James Henry Smith I'm sorry, Eric Dubay and Mark Sergeant lied to you. You fell for an internet joke.

[@ishna2023]

Loved the explanation, it was so simple and so good.

[@om7official723]

Thank you sir, love from India 🇮🇳.

[@ellmou]

this guy made me get it in 5 min my fro took 4 hours

[@cimmik]

How did we discover that Earth is an ellipsoid?

[@QuillWorks]

I wonder if they sell ellipsoid globes? They should

[@vikramaditya209]

How variation in ionosphere is helpful in detecting earth quake and provides early warning.

[@nazimL1011]

great stuf.....been trying to come to terms with geometric altitude produced by the GNSS for use by ADS-B out.

[@jamesherrick3751]

good stuff

[@pinakisinhabiswas1908]

2:20 mistake.. what was explained was not semi major and semi minor axis but just major and minor axis.. semi would be from the centre,not from one end to the other!!

[@GeoMindzcom]

Hi! I pinned a comment to the top of the comment section on this very subject. Thank you for the catch.

[@pinakisinhabiswas1908]

@@GeoMindzcom ohh,yup just checked it out!! Thanks for the acknowledgement!!

[@joaquinfabrega]

Great video!

[@peteschupp4545]

So geoid is only an illustration of the value of gravity on different places on the surface but not the real shape it Has? I mean gravity anomalies due to differing mass density has nothing to do with the actual form

[@victoriamurwira9691]

well explained, thank you

[@tasnovayesmin755]

Thanks sir

[@GeoMindzcom]

You are very welcome!

[@mohitknoledge5830]

Nice man

[@abvmoose87]

Is it possible to get a hold of a real, non exagerated, reference model of the earth elipsoid? Is it possible to male out the oblateness of the earth from the reference model with the naked eye or is it too small to be noticed if viewing an accurate reference model?

[@GeoMindzcom]

I don't know of anything like that, but I think that with any globe of manageable physical size, you would not be able to tell its distortions off of spherical with the naked eye.

[@Trinitykiller00]

Great video Sir. As a Muslim, we already knew this 1400 years ago ! How you may ask ? well it's written in the Quran that the shape of the earth is more like an ostrich egg. [79:30] ''He made the earth egg-shaped'' Allah knows best.

[@Wulst57]

Quite a mistake at 1:15 right? Are you sure you don’t mean 12,756.20 km? Otherwise it would be bigger than the sun ;)

[@GeoMindzcom]

I am not sure where you mean. The diameter of the earth is about 12.746 million meters, or about 12,746 km, which is what I am showing on the screen there, right?

[@Wulst57]

GeoMindz.com you’re absolutely right, I was misreading that one. I shouldn’t study for cartography that late at night ;)

[@GeoMindzcom]

Okay. Whew! It is completely possible that there might be error somewhere, but I just couldn't find it. Thank you!

[@Wulst57]

@James Henry Smith nah

[@S.P20sss]

Great

[@victorneely7964]

So if the earth is an ellipsoid why are the photos that NASA shows us a sphere? They really need to make up their minds because it can't be both of them;-)

[@Kemal-s8w]

Did you miss the part where he says the flattening is only 1/300? The polar circle is smaller than the equatorial circle by only a factor of 1 out of 300. Let me give you an experiment. Take a stick as big as your computer screen. Then take another stick of same size but cut out 1/300 part of this stick. Then place the two sticks criss-cross like a + sign. See if you can tell one stick is smaller than the other. Better yet rotate the + sign so you forget how you placed it and then try to tell which one is the smaller stick. Then when you realize your argument was stupid, come back and acknowledge that you learnt something.

[@victorneely7964]

@@Kemal-s8w An ellipsoid has a specific mathematical formula so you saying the flattening is only 1/300 wouldn't qualify it to be an ellipsoid so there's that. And forget all your gibberish all you have to do is look at a picture of something to determine if a square is a square or a triangle a triangle or a sphere a sphere.

[@Kemal-s8w]

@@victorneely7964 Any sphere with non-zero flattening is an ellipsoid (also a spheroid) and not a sphere mathematically. Flattening of a spheroid is a mathematical term similar to eccentricity in ellipse. Here is a basic intro: en.wikipedia.org/wiki/Flattening And no if the flattening is too small you won't be able to make out from naked eye. Complete the experiment I told you. That experiment quite literally lets you visualize the amount of flattening earth has. See if you can make out the difference in stick sizess. Children's books use the word sphere because that is a decent approximation for kids. But adults having any exposure to science are expected to know that earth is an oblate spheroid. Also it's okay to be wrong once in a while. If one wants to be pedantic, an ellipsoid is a more generalized spheroid in that while a a spheroid is a sphere compressed from top and bottom, an ellipsoid is additionally also compressed from one other axis. This means that out of the 3 axes of an spheroid, 2 are same whereas all 3 CAN be different for an ellipsoid. Hence every spheroid is an ellipsoid but not every ellipsoid is a spheroid. If you are curious, earth's shape of an oblate spheroid comes directly from its rotation. In fact any rotating fluid body will be slightly flatter at the equator and thus its shape will be that of an spheroid. If you are even more curious, you can derive the figure of 1/300 from the equilibrium of gravitational force and centrifugal force if you can do a little bit of math (equivalent to what we learn at 17-18 years age in India for those who choose physics)

[@Kemal-s8w]

@@victorneely7964 Firstly I didn't say gibberish. I gave you an experiment to visualize a flattening of 1/300. The point is that two lengths which vary by a factor of 1 out of 300 are practically indistinguishable by the human eye. Hence it is impossible to tell from a photograph that earth is not a perfect sphere even though it obviously is not a perfect sphere..

[@mtoseeqhaider5545]

Please write which you say we can't understand your language because you speak fastly

[@2wali]

What if it is flat?

[@GeoMindzcom]

If the world is flat then mapping suddenly becomes a lot easier. LoL :-) But, we're pretty locked down on the round world. See the Eratosthenes video: kzbin.info/www/bejne/nJWmdGZ6ndSqn6c

[@FierceHamster]

@@GeoMindzcom but all the people of that time believed it to be flat and that the sun was a much smaller, local source. If it were, it would provide the same effect. Do you have any links to videos which show an exact modern duplication of this experiment? I looked thinking there would be thousands and cannot find one. Be great to see split screen at noon - with people at a well on the solstice and at the precise time with an atomic clock someone in Alexandria measuring a shadow from an obelisk or other tall structure matching his measurements. I'd also like to see how his errors 'cancelled each other out' as well - as the issues you alluded to in your video - in addition to the extreme margin of error of having a slave driven cart with measured pebbles somehow matching the modern distance traversed by planes of 843 km. Would be interesting to see how his erroneous numbers that he used contributed to the greatest fluke in all history. All pdf's I have found that try to duplicate it all seem to be fudging whatever they can to match the numbers we now have for the earth rather than going in entirely blind and letting the data that Eratosthenes faced guide them. Again, none of these modern experiments think to capture this apparently easy reproducible experiment on video for us to enjoy...

[@GeoMindzcom]

​@@FierceHamster It sounds like this may be a great excuse for me to finally take a trip to Egypt and video the experiment. Though I don't think I have access to an atomic clock. :-) But, actually, I think you can replicate the experiment without being in Egypt. Here is a link to someone who did something similar: www.millersville.edu/physics/experiments/058/index.php A much smaller sun that is closer to a flat earth could produce a similarly appearing phenomena. We used to talk about that in class. I think I read that the Chinese used that approach and estimated how far the sun would be away from the earth in that situation. I hope I am able to get back to making some GeoMindz videos in the not too distant future. Maybe I need to return to this topic.

[@FierceHamster]

@@GeoMindzcom looks pretty good. he didn't seem too concerned to keep the measured cities on the same meridian - not sure if that contributed to his estimate of earth's circumference being 58,000km.

[@Hightower420]

Why should earth be flat and other planets not? Makes no sense.

[@sandeepsingh-mu7lp]

No paw

[@xerxiusmaximus]

These are “technical terms,” lol….

[@flatearthbanjo]

Good job passing on the programming you went in college but the fact is, earth is Flat!

[@bobartor910]

And you've got a map to prove it I suppose. LMAO

[@altairibnlaahad6593]

Bob Artor he’s just being sarcastic (I sure hope so)

[@kakapofan6542]

Well how about you fully learn how math works and how you can use it to prove yourself or others wrong. Otherwise how can you really say whos being brain washed