Confusion About Rotating Camera Around Point

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DishSoap    698

So I have a requirement to rotate around a scene. The scene is just a revolving sun with an earth and moon revolving around that.

I have to use gluLookAt() to rotate around that sceen. I do it with this code:

GLdouble theta = -anglex * PI / latiGrid;
GLdouble phi = angley * 2 * PI / longiGrid;

gluLookAt(eyeZ * cos(theta) * sin(phi), eyeZ * sin(theta), eyeZ * cos(theta) * cos(phi), 0, 0, 0, 0, 1, 0);


Where anglex and angley is simply the difference in angles of the X and Y screen coordinates... First I extracted this code from a similar project, so I was hoping someone could explain why it works in the first place. How are the eye coordinates derived exactly? I'm a bit at a loss of how this works.

Also, It rotates fine in the horizontal direction, but in the vertical direction it gets to the top it translates the orbiting earth from one end to the other.

Edited by DishSoap

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Vortez    2714

you could try rotating one axis at the time and see which one dosen't work properly. Personally i would just rotate/translate the scene to achieve the same effect using gltranslate/glrotate, but if you have too... try what i said above.

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DishSoap    698

I would normally do that, yes. But this is for a class that requires I do it this way ^^.

The code I have is functional other than the small bug I have. Just wondering how the components for eyeX, eyeY, eyeZ are derived. If there is an article or online resource anyone knows about that I can read on it.

Edited by DishSoap

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Shawn619    342

Just wondering how the components for eyeX, eyeY, eyeZ are derived

I'll give you an idea on how I would approach this assignment and answer your question at the same time.

For rotation, you say that your rotation method is working, instead of using the traditional glrotate, so i'll leave the rotation alone.

For translation, the first 3 components of gluLookAt are the position of your eye in world space, which you seem to have calculated correctly, assuming your rotation are correct.

The next 3 components are where your eye will be looking. So, in your scenario of an earth orbiting around a sun, assuming your sun in centered at the origin, these 3 components would be (0,0,0), which would have your eye looking towards the origin(at the sun).

http://www.opengl.org/sdk/docs/man2/xhtml/gluLookAt.xml

Also, shouldn't

gluLookAt(eyeZ * cos(theta) * sin(phi), eyeZ * sin(theta), eyeZ * cos(theta) * cos(phi), 0, 0, 0, 0, 1, 0);


be

gluLookAt(eyeX * cos(theta) * sin(phi), eyeY * sin(theta), eyeZ * cos(theta) * cos(phi), 0, 0, 0, 0, 1, 0);


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DishSoap    698

Thank you! Turns out since eyeX = 0, eyeY = 0 and eyeZ = -23 the programmer who orgininally used those parameters simply used the component eyeZ as a distance since he is using cartesian coordinates.

I appreciate the help :D

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