closing tag is in template navbar
timefactors watches



TZ-UK Fundraiser
Results 1 to 26 of 26

Thread: The Earth's Curvature

  1. #1
    Master
    Join Date
    Dec 2010
    Location
    NW Leics
    Posts
    8,485

    The Earth's Curvature

    This is a photo that I took in Wales in March, on the Pembrokeshire coastal path.



    The camera (actually a Samsung phone) was only about 20 - 30 metres above sea level when this was taken. But I wondered if I'd be able to see the curve of the horizon if I compressed the pic sideways, like this (image is cropped but shows the whole breadth of the first image:



    Although it's tempting to blame the curvature present in the image on lens distortion, I don't think that's the case here. The horizon was actually slightly below the centre of the image, so any barrel distortion would tend to suppress the curve, not exaggerate it. However I have no idea how to do the maths for the degree of curvature you'd expect to see from that elevation.

    However, I suspect that is just an exaggerated view of the Earth's curvature.

    Anyone any thoughts?

  2. #2
    Grand Master PickleB's Avatar
    Join Date
    Sep 2009
    Location
    M25 J6 UK
    Posts
    18,720
    From the Samsung SM-A528B user manual:

    Your device’s camera features a wide-angle lens. Minor distortion may occur in wide-angle pictures or videos and does not indicate device performance problems. To correct the distortion in pictures, tap ⚙ on the preview screen, tap Format and advanced options, and then tap the Ultra wide shape correction switch to activate it.

    Did you...?

  3. #3
    Grand Master hogthrob's Avatar
    Join Date
    Feb 2007
    Location
    Essex, UK
    Posts
    17,484
    You do realize that you have a decent percentage of TZ-UKers holding rulers to their screens?

    My result was that in the larger picture, the centre of the horizon is slightly higher than at the sides; presumably this does demonstrate that the earth isn't flat.

  4. #4
    Master
    Join Date
    Dec 2010
    Location
    NW Leics
    Posts
    8,485
    Quote Originally Posted by PickleB View Post
    From the Samsung SM-A528B user manual:

    Your device’s camera features a wide-angle lens. Minor distortion may occur in wide-angle pictures or videos and does not indicate device performance problems. To correct the distortion in pictures, tap ⚙ on the preview screen, tap Format and advanced options, and then tap the Ultra wide shape correction switch to activate it.

    Did you...?
    I didn't. But the wide angle distortion described there would act against the curve visible in the image, it wouldn't enhance it.

  5. #5
    Grand Master PickleB's Avatar
    Join Date
    Sep 2009
    Location
    M25 J6 UK
    Posts
    18,720
    Quote Originally Posted by monogroover View Post
    I didn't. But the wide angle distortion described there would act against the curve visible in the image, it wouldn't enhance it.
    See this article, please, if seeing really is believing, here’s a few steps you can take to see the curve and in the comments: "Mainstream science tells us we can’t see the curvature until somewhere around 60,000-130,000 feet."

  6. #6
    Grand Master Saint-Just's Avatar
    Join Date
    Apr 2007
    Location
    Ashford, Kent
    Posts
    30,013
    The very existence of the horizon is an illustration of the Earth's, curvature (perpendicular to the one your compression appears to show); should you climb to a pole or mast, you would see further (hence crows nests in sailing ships).
    'Against stupidity, the gods themselves struggle in vain' - Schiller.

  7. #7
    Grand Master PickleB's Avatar
    Join Date
    Sep 2009
    Location
    M25 J6 UK
    Posts
    18,720
    Quote Originally Posted by monogroover View Post
    I didn't. But the wide angle distortion described there would act against the curve visible in the image, it wouldn't enhance it.
    Why do you say "the wide angle distortion described there would act against the curve visible in the image, it wouldn't enhance it", please? I ask as I cannot find any description of the distortion in that user manual. Have you heard of barrel distortion...see this WikiLink?

    Again, from the user manual, "Customising camera setting...Pictures...Ultra wide shape correction: Set the device to correct distortion in pictures taken with the Ultra wide camera." Again...did you?

  8. #8
    Master unclealec's Avatar
    Join Date
    Feb 2011
    Location
    Manchester
    Posts
    6,610
    The Earth is round?

  9. #9
    Grand Master Saint-Just's Avatar
    Join Date
    Apr 2007
    Location
    Ashford, Kent
    Posts
    30,013
    Quote Originally Posted by PickleB View Post
    Why do you say "the wide angle distortion described there would act against the curve visible in the image, it wouldn't enhance it", please? I ask as I cannot find any description of the distortion in that user manual. Have you heard of barrel distortion...see this WikiLink?

    Again, from the user manual, "Customising camera setting...Pictures...Ultra wide shape correction: Set the device to correct distortion in pictures taken with the Ultra wide camera." Again...did you?
    I believe he says that because the horizon is in the lower half of the picture, when the expected distortion would curve the horizon the other way. I am not sure that assumption is correct even if it is a reasonable one to make.
    'Against stupidity, the gods themselves struggle in vain' - Schiller.

  10. #10
    Pembrokeshire is beautiful

    Sent from my M2101K6G using Tapatalk

  11. #11
    Master
    Join Date
    Dec 2010
    Location
    NW Leics
    Posts
    8,485
    Quote Originally Posted by PickleB View Post
    Why do you say "the wide angle distortion described there would act against the curve visible in the image, it wouldn't enhance it", please? I ask as I cannot find any description of the distortion in that user manual. Have you heard of barrel distortion...see this WikiLink?

    Again, from the user manual, "Customising camera setting...Pictures...Ultra wide shape correction: Set the device to correct distortion in pictures taken with the Ultra wide camera." Again...did you?
    Again: no, I didn't.

    So: here's a graphic that represents what barrel distortion does to an image:



    In this case, the line of the horizon - because it's below the centre of the image - is analogous to one of the lines below the centre of the graphic on the left. But the horizon line in the compressed image I posted curves upwards. Hence, if barrel distortion has compromised the image at all, then it has suppressed the curve. It hasn't caused it, or exaggerated it.

    I'm open to the possibility that the second image has been influenced by pincushion distortion, but I don't see how a relatively wide lens on a phone would do that.

  12. #12
    Grand Master PickleB's Avatar
    Join Date
    Sep 2009
    Location
    M25 J6 UK
    Posts
    18,720
    Quote Originally Posted by Saint-Just View Post
    I believe he says that because the horizon is in the lower half of the picture, when the expected distortion would curve the horizon the other way. I am not sure that assumption is correct even if it is a reasonable one to make.
    In which case, if the photo is uncropped, I should have referred the OP to pincushion distortion rather than barrel.

    The best way to investigate the presence (or absence) of distortion would be if the OP were to return to the Pembrokeshire Coast National Park and take a series of photo with the horizon at different heights in the frame.

    If you look at the StreetView photos associated with the link above and scan left to right, you can see that the horizon in not consistently flat or, apparently, slightly curved. To me, that indicates that Google are aware of lens distortion and apply some correction selectively.

  13. #13
    Grand Master PickleB's Avatar
    Join Date
    Sep 2009
    Location
    M25 J6 UK
    Posts
    18,720
    OP...Nikon's best lenses have some distortion, in particular their wide angle lenses...see LINK. I don't think it reasonable to expect a Samsung phone to do any better.

    If you cannot accept the science...see the ink in my post above and this link too...then I must resort to:




  14. #14
    Grand Master MartynJC (UK)'s Avatar
    Join Date
    Dec 2008
    Location
    Somewhere else
    Posts
    12,683
    Blog Entries
    22
    I disagree the earth is flat and I have a picture to prove it!

    “ Ford... you're turning into a penguin. Stop it.” HHGTTG

  15. #15
    Master subseastu's Avatar
    Join Date
    Oct 2012
    Location
    Ashby, uk
    Posts
    2,334
    Quote Originally Posted by unclealec View Post
    The Earth is round?
    No. It's an oblate spheriod. Balanced on the back back of turtles

    Sent from my SM-G991B using Tapatalk

  16. #16
    Grand Master
    Join Date
    Jul 2008
    Location
    UP North.
    Posts
    13,122
    Quote Originally Posted by hogthrob View Post
    You do realize that you have a decent percentage of TZ-UKers holding rulers to their screens?

    My result was that in the larger picture, the centre of the horizon is slightly higher than at the sides; presumably this does demonstrate that the earth isn't flat.
    You can't just say the earth isn't flat!.

    I need some facts to prove this please.


  17. #17
    thats the lens distorting, even very fancy huge pro lenses do it and it is corrected in the camera or software

  18. #18
    Master MrLion's Avatar
    Join Date
    Feb 2011
    Location
    Northern Hemisphere
    Posts
    2,609
    Quote Originally Posted by unclealec View Post
    The Earth is round?
    No no, it's merely curved

    Sent from my DN2103 using Tapatalk

  19. #19
    Quote Originally Posted by monogroover View Post




    However, I suspect that is just an exaggerated view of the Earth's curvature.


    Imagine a this protractor is the size of the earth, the distance between one degree is 111km. I'm not sure of the distance between the far left and right of your image, but at 20m high the horizon would be around 16km away, so perhaps 32km between the edges of your image wouldn't be enough to see a curve.

  20. #20
    Grand Master oldoakknives's Avatar
    Join Date
    Sep 2012
    Location
    United Kingdom
    Posts
    20,882
    Blog Entries
    1
    Quote Originally Posted by MartynJC (UK) View Post
    I disagree the earth is flat and I have a picture to prove it!

    If the Earth really was flat cats would have pushed everything off it by now.
    Started out with nothing. Still have most of it left.

  21. #21
    If that is Pembrokeshire then what you are seeing is the Hump Back Wales.
    "Bite my shiny metal ass."
    - Bender Bending Rodríguez

  22. #22
    Master
    Join Date
    Dec 2010
    Location
    NW Leics
    Posts
    8,485
    Quote Originally Posted by PickleB View Post
    OP...Nikon's best lenses have some distortion, in particular their wide angle lenses...see LINK. I don't think it reasonable to expect a Samsung phone to do any better.

    If you cannot accept the science...see the ink in my post above and this link too...then I must resort to:



    I'm trying not to, but: wide angle lenses distort in a particular way that wouldn't cause the upward curvature of a line below the centre of the image. I'm sorry if you haven't understood that.

  23. #23
    Master
    Join Date
    Dec 2010
    Location
    NW Leics
    Posts
    8,485
    Quote Originally Posted by xellos99 View Post
    thats the lens distorting, even very fancy huge pro lenses do it and it is corrected in the camera or software
    Yes, this is well understood. I wonder if the curvature of the horizon in the image is a product of over-correction by the phone's camera app? That at least would make sense.

  24. #24
    Master
    Join Date
    Dec 2010
    Location
    NW Leics
    Posts
    8,485
    Quote Originally Posted by PickleB View Post
    In which case, if the photo is uncropped, I should have referred the OP to pincushion distortion rather than barrel.

    The best way to investigate the presence (or absence) of distortion would be if the OP were to return to the Pembrokeshire Coast National Park and take a series of photo with the horizon at different heights in the frame.

    I think an excellent experiment would be to take a pic on a clear day with a better camera, with the horizon as centred as possible. Then to do the same again, with the camera upside down. Then to compare the two images. Next time I have a clear view of a horizon from a bit of elevation, I'll do that.

  25. #25
    Master vagabond's Avatar
    Join Date
    May 2006
    Location
    Here and There....
    Posts
    6,702
    Blog Entries
    1
    Quote Originally Posted by monogroover View Post
    I think an excellent experiment would be to take a pic on a clear day with a better camera, with the horizon as centred as possible. Then to do the same again, with the camera upside down. Then to compare the two images. Next time I have a clear view of a horizon from a bit of elevation, I'll do that.

    Wouldn't the 2nd picture just prove that the bottom half of the world is round too?

  26. #26
    Grand Master MartynJC (UK)'s Avatar
    Join Date
    Dec 2008
    Location
    Somewhere else
    Posts
    12,683
    Blog Entries
    22
    There is an excellent paper here: Lynch Curvature 2008.pdf That explains the science of observing the curvature of the earth. Spoiler - approx 35,000ft is needed to view the curvature. Please read for details.

    I did a bit of distortion edit on the original pic

    Last edited by MartynJC (UK); 17th May 2024 at 08:24.
    “ Ford... you're turning into a penguin. Stop it.” HHGTTG

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Do Not Sell My Personal Information