[6.837] Project 3, skycam clarification or restatement.

[Hector Briceno <hbriceno@graphics.lcs.mit.edu>]

Hi,
	I have seen some people implementing the SkyCam incorrectly, so I
figure I would restate what we are asking for:

Here is what the problem set says:

"The Sky Cam will set the view to the position and orientation to the 'sky
camera'. In sky camera mode the mouse should exhibit the following
behaviors."

"With the right button down, moving the mouse right causes the
sky camera to translate right (the x direction of the sky camera's frame),
moving to the left translates left,"

  So basically it moves on the direction of the camara's x axis.  So when
  the camara moves right, things will move left.

"moving up translates up (the y direction of the sky camera's frame), and
moving the mouse down translates down."

  So this is like moving the camera up if the camara is horizontal.  But
  now imagine that the camara is looking down, the y axis is parallel
  to the ground, so moving the camera along the y-axis is like moving it
  parallel to the ground (like a shot from an airplane looking down).
  remember you are moving along the camera's y-axis which might not (and
  usually is not) aligned with the model's y-axis.


"When the left button is pressed, moving the mouse right causes a
rotation about the camera's y-axis by a negative angle, moving the mouse
left causes a positive rotation"

  This is rotating the camera, like if it was on a tripod, and the tripod
  is aligned with the camera's y-axis.

"moving up causes a positive rotation about the x-axis, and moving the
mouse down causes a negative rotation about the camera's x-axis."

  This is a camera tilt operation, tilting the camera up or down.



With these 4 operations you can place the camera anywhere in the world and
orient it at any angle.

I hope this helps or clarifies some things.  I don't think I have added
anything or that I have writting anything is inconsistent with what is in
the project handout. i.e. if you read the project handout _carefully_ you
came or would have come to the same interpretation.

Hector Briceno

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