Planet Four Talk

#yardangs or not?

  • floriel by floriel

    would these also qualify as #yardangs ?

    Posted

  • p.titchin by p.titchin

    Quite an eroded surface but the faint top left to bottom right parallel lines I would say are Yardangs. ~ Pete

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  • Kitharode by Kitharode moderator in response to floriel's comment.

    Hi floriel. I agree with Pete that the top left to bottom right lines are yardangs. I also agree that the surface is very eroded.

    Question is (and I don't know the answer): Is this a yardang region which is becoming eroded, or is it an eroded surface that is becoming yardanged (or whatever the word is)? :-X

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  • floriel by floriel

    To my knowledge (which in this case relies on https://en.wikipedia.org/wiki/Yardang), yardangs are what's left behind from abrasion.
    If I interpret the picture correctly, the diagonal lines are lower than the surrounding area. In this case not the lines but the rest could be yardangs, but theres so much "rest" that I'm not sure if it would fit this definition of yardangs.
    But then again, I'm still very new to this and know next to nothing about it.

    As for the diagonal lines: I used #trainlines as a tag for such long parallel formations and #striations for shorter, jet mainly parallel formations.

    Posted

  • floriel by floriel

    After reading this blogpost I'm even more confused

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  • floriel by floriel

    And just to keep all links together: our brain creates the illusion of inverted topography

    ...So here we would have an originally flat surface battered with holes on 95% of it's area and the parts that remained high and flat are somehow aligned in parallel lines???

    Posted

  • floriel by floriel

    I guess a 3D model with adjustable light direction and camera angle would help me and others to wrap their brains around it.
    Is there anyone around who knows how to do such interactive 3D animations and has too much time to kill? ;-P

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  • floriel by floriel

    But the best way to handle this confusion would probably be to implement a "rotate image for top-left lighting" button. Or to make that adjusted rotation the default and the original rotation optional.

    Posted

  • mschwamb by mschwamb scientist, translator in response to floriel's comment.

    The parallel lines might have formed first as yardangs and then surface was sculpted in other ways later than made the bumpy appearance. I see if someone else on the team can give more detail.

    Cheers,

    ~Meg

    Posted

  • mschwamb by mschwamb scientist, translator in response to floriel's comment.

    It's hard to do 3D for most of the HiRISE images because we don't have enough data to do stereo. Stereo or 3-D imaging requires to different perspectives. Our eyes are separate by a distance so that we can get depth perception by our brains' combining the two images together. We have more on stereo imaging in this blog post. Most areas HiRISE takes doesn't have multiple images close in time at different orientations.

    Cheers,

    ~Meg

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  • floriel by floriel

    The 3D model I was talking of wasn't supposed to be from ream data, but simply a fictional landscape similar to what you encounter on mars, for educational purposes (on the optical illusion) only.

    Posted

  • floriel by floriel

    Can we calculate the sunlight's direction with the given position/ orientation data (Azimuth, Angle)? If so, what's the formula?

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  • p.titchin by p.titchin

    Hi floriel. Your image lists the 'sub solar azimuth'. angle. This gives you the angle to the spot where the sun is overhead and so the direction from which the image is lit. In your example, it is 42.0193°. It is measured from '3 o'clock' on the image, and so the light is from roughly the lower right.corner. Hope this helps. ~ Pete.

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  • Kitharode by Kitharode moderator

    As usual, Pete has it absolutely right. There's also a really good blog post relating to your question with an excellent diagram.

    http://blog.planetfour.org/2015/03/12/geometry-of-hirise-observations-is-on-talk/ 😃

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