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Am 28.08.2014 17:32, schrieb Bald Eagle:
> Thomas de Groot <tho### [at] degroot org> wrote:
>
>> I often use a camera angle of 80 .... In combination with:
>> right x*image_width/image_height
>
> So, I guess I was under the impression that the above equation was the default
> setting when you declare a camera object?
>
> I guess I'm struggling a little bit - I seem to be at that awkward point where I
> know enough to ask questions, but know too little to ask GOOD questions. :\
>
> all of these attributes seem to be interrelated to one another in a sort of
> circular-logic that I can't untangle. I see you declaring RIGHT - how does
> that affect UP - or doesn't it?
What the up, down and direction vectors do (at least when you also
specify an angle and look_at point) is simply define the coordinate
system in which the camera is set up before being rotated to the look_at
point and zoomed to fit the angle, as well as the aspect ratio of the
image; these three vectors should be perpendicular to each other, unless
you are after some special effect (such as a that of a tilt-shift lens);
the ratio of the right vector's length vs. the up vector's should match
the ratio of the image width vs. height (unless you use an image format
that has non-square pixels, but you rarely need those these days). If
you're not using angle, the ratio of the direction vector's length to
that of the right vector's also determines the field of view, but with
angle specified the direction vector's length is entirely irrelevant.
>> Something that might help too is playing with the camera look_at
>> distance in relation to its location.
>
> Hmm. I'll have to experiment with that, since I didn't realize it had any
> effect. I typically just use it as a camera orientation vector. I generally
> don't care if the vector length is 0.01 or 100,000 so long as they lie on the
> same line of sight. What should I be expecting / looking for?
The distance to the look_at point is irrelevant, the look_at point just
determines the camera's orientation.
The camera is oriented by first rotating the camera around the up vector
until the camera looks at the look_at point's projection onto the
right/direction plane, then tilting the camera up or down to look at the
actual look_at point.
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