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Thread: finding the axis of a sphere, Loomis head drawing

  1. #1
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    finding the axis of a sphere, Loomis head drawing

    Hello all, So I finally got the Andrew Loomis book for drawing heads. At the beginning ( going right back to basics! ) you start off with a sphere and mark the axis ready for constructing the rest of the head. I am struggling though because I am not sure exactly how you accurately find the axis lines on the sphere. I know roughly where they would go and can do an alright job ( I think ) with guess work, but I would like to be more accurate with these measurements, but I am not sure how. Is there a method or a way of finding the axis / slicing the sphere accurately or is it down to guess work?

    I realise this seems like a novice question, but you have to ask to learn right?

    Just a quick image of the paper next to me, it's not the best example as they are just doodles/ not even accurate circles but hopefully it gives you an idea what I am talking about if the text above made no sense.
    Thanks
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    I am not sure if it's actually marking the axis I am struggling with or more wrapping it around the sphere, knowing exactly the point it falls off at / you can see to. Am I making sense or talking gibberish?
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  3. #2
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    The Loomis method gives you an approximation of the head structure, so I think he is just eyeballing his axis and slices. Don't try to be too precise...
    Grinnikend door het leven...
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    One thing you might do if you're having trouble visualizing how the sections across the spheres look is to
    a) get a real sphere of some sort and draw the lines on it, then draw it from life
    b) use a 3D application, draw a sphere and select the edges that correspond to the sections (see attachements)

    With practice you'll get a feeling for how they look and you'll be able to apply that knowledge to any sphere from any point of view.

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  6. #4
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    Good advise thanks guys
    @Benedikt what program are you using there please?
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    draw a sphere

    mark a spot on the sphere

    draw two lines tangent to the sphere that also pass through that point.

    and then draw from that point a line perpendicular to both lines

    that line intersects the center of the sphere = axis.
    The heights by great men reached and kept,
    Were not attained by sudden flight,
    For they, while they companions slept,
    Were toiling upwards in the night"

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    @Amir0 not to sound extremely stupid.. but I don't fully understand
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    Last edited by Amir0; April 26th, 2014 at 11:46 AM.
    The heights by great men reached and kept,
    Were not attained by sudden flight,
    For they, while they companions slept,
    Were toiling upwards in the night"

    (Henry Wadsworth)
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    Quote Originally Posted by Stephen H View Post
    Good advise thanks guys
    @Benedikt what program are you using there please?
    Looks like he's using Modo, but you can easily do the same thing in any 3D program (i.e., Sketchup or Blender, both of which are free.)
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  12. #10
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    Yeah sorry Amir0, I am struggling to follow what you mean
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    if I understand your problem correctly, what you are struggling to do is to paint a (2d projection of a) sphere, and then plot an axis line on it.

    An axis of a sphere is a shorthand term denoting the sphere's axis of symmetry. obviously it has an infinite number of them. However all of them have the following properties:

    1. They all pass through the sphere's center
    2. They are all perpendicular to the sphere's surface.

    Using these 2 mathematical properties a sphere's axis can be plotted through numerous geometric methods. one of which i've tried to present... and apparently failed.
    The heights by great men reached and kept,
    Were not attained by sudden flight,
    For they, while they companions slept,
    Were toiling upwards in the night"

    (Henry Wadsworth)
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    I have to admit I couldn't follow Amir0's explanation either, but the way I approach finding the axis is by using it's symmetry as well.
    First the axis will divide the sphere/circle into even halves. The entry point then is an equal distance away from the circle line as the exit point.

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    This disregards perspective though. To be more correct you'd have to construct a box around the sphere or use 3d software.
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  16. #13
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    Amir0, I am going to have a read over all the info you have given and see if I can get my brain in gear.

    Schraverus, I am really liking your suggestion, definitely something easy to remember and use. You mentioned it might not be correct in terms of perspective, which is a bummer, but at the same time, this is just for getting the basics for building construction lines on a head showing the angle of the face etc, so hopefully this will be what I need for that!

    So that worked great for the horizon line, to get the vertical line is it just a case of starting with another straight line but diagonal in the opposing direction, or is it a little more complicated then that?
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