Sebastian Kasperski napsal(a):
> Chris B wrote:
> 
>> Have you tried playing around with camera type cylinder 3 (vertical
>> cylinder, viewpoint moves along the cylinder's axis)?
>>
>> plane {y,0
>>   pigment {checker}
>>   finish {ambient 1}
>>   scale 0.5
>> }
>> camera {
>>    cylinder 3
>>    angle 360
>>    up y
>>    location <0,0.5,0>
>>    look_at  <0,0.4,1>
>> }
> 
> The cylinder type 3 realizes some kind of parallel projection, which is
> clearly not what I need. (It's only parallel to the xy-plane though)
> 
>> The docs seem a little light on an explanation of this and I don't know if
>> this is exactly the sort of distortion you're trying to achieve.
> 
> I found the documentation on this to be of little help as well. What I want
> to do is a central projection like you get from a pinhole camera, just with
> the image plane being a cylinder. The result would be a full panorama view,
> somethiung like this:
> 
> plane {
>   y,0
>   pigment {checker}
>   finish {ambient 1}
> }
> camera {
>   cylinder 1
>   angle 360
>   up y
>   location <0,0.5,0>
>   look_at <0,0.5,1>
> }
> 
> I this case the cylinder reaches from 0 to 1 ("up y" defines the cylinder to
> be of height 1, and the viewpoint is in the middle.) What I need for
> example would be a viewpoint at <0,1,0> and a cylinder reaching from y=0,5
> to y=1.0 (Viewpoint on top and looking down through the cylinder)
> I found a kind of cheap workaround by simply defining a higher cylinder (in
> this case y=0.5 to y=1.5) and then cropping all the images, which works,
> but is quite uncomfortable.
> 
>> If this fails, you may be able to achieve what you want in two passes:
>> If you are trying to map the scene to a cylinder and be able to place the
>> camera so that it's looking down through the cylinder, you could first
>> render the scene using a cylinder 1 camera, then use that image as an
>> image_map that you map to a cylinder (ambient 1) and render the result.
>> You'll then be able to place the camera wherever you want relative to the
>> cylinder.
>> Likewise, if you want to just add a perspective distortion to the result
>> you could map the image from the first render to a plane and move the
>> camera around for the second render.
> 
> If I got that right, then it is not what I mean. See my example above, I
> think it should make it clearer.
>> Otherwise, a few more words describing what you're trying to achieve would
>> be helpful, or a link to an image that uses the sort of projection you
>> seek.
>>
>> Regards,
>> Chris B.
> 
> I am simulating a real camera, so the projection is given by the hardware
> and can't be changed. The camera also flips the image vertically, so that
> it goes from 0° on the left to 360° on the right. (this is in positive
> direction (counter clock wise) instead of povray, which does it in negative
> direction(clock wise)). A solution would be again to flip all images by
> hand, but since i'm doing an animation with 250 frames, this would be
> impracticable as well. So is there a way to change the coordinates of the
> image plane in povray? For normal cameras, I think it can be done using
> the "up" and "right" vector, but I couldn't find out how the "right" vector
> is used for cylindrical cameras. 
> 
> Best regards
> Sebastian
You could use a camera_view pigment in MegaPov to do the cropping and 
flipping for you. This also causes that only the bottom half (the part 
not cropped) is rendered.

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