looking at the docs, i see that a cylindrical camera makes an image of
the outside of the cylinder, which presumably has no radius.  what i
would like to do is specify a radius (in order to envelope objects) and
then create the image based on the inside of the cylinder.  this (i
think) would have the effect of "unrolling" the object into two
dimensions, ready to be used as a template for image maps, bumpmaps, or
image pattern maps and could be rolled back onto the object using
cylindical mapping.  this would eliminate the need to divide a model
into two halves and then use planar image mapping as was done, for
example, in h.e. day's raptor model.  a spherical cam that could also do
this would be similarly useful.  would this be difficult to implement? 
do others think this would be useful?

Post a reply to this message

Two suggestions:

First, try using the sphere_camera (spherical_camera) in MegaPOV.  To quote
from the docs, '...If you render an image with a 2:1 aspect ratio and map it to
a sphere using spherical mapping, it will recreate the scene!'

Secondly, if you're working with meshes, try using Steve Cox's UV Mapper:
http://home.pb.net/~stevecox/uvmapper.htm

Gilles Tran has a very helpful tutorial for working with it here:
http://www.mediaport.net/Artichaud/Tran/sources/tutuve.htm

Hope this helps...

ryan constantine <rco### [at] yahoocom> wrote in message
news:39721EB9.554BD97C@yahoo.com...
| looking at the docs, i see that a cylindrical camera makes an image of
| the outside of the cylinder, which presumably has no radius.  what i
| would like to do is specify a radius (in order to envelope objects) and
| then create the image based on the inside of the cylinder.  this (i
| think) would have the effect of "unrolling" the object into two
| dimensions, ready to be used as a template for image maps, bumpmaps, or
| image pattern maps and could be rolled back onto the object using
| cylindical mapping.  this would eliminate the need to divide a model
| into two halves and then use planar image mapping as was done, for
| example, in h.e. day's raptor model.  a spherical cam that could also do
| this would be similarly useful.  would this be difficult to implement?
| do others think this would be useful?

Post a reply to this message

no offense, but i think you missed my point altogether.  i have a model
constructed.  i want to see the front and the back of the model all at
the same time.  i want to use the image and bring it into a paint
program.  there i will color code areas for use as image pattern maps. 
currently, the only method one can use is to do an orthographic
projection to make the image.  then, after making the textures, use
planar mapping on the object.  using this method, however, requires two
halves of the original object and an image map for the top and one for
the bottom.

Alan wrote:
> 
> Two suggestions:
> 
> First, try using the sphere_camera (spherical_camera) in MegaPOV.  To quote
> from the docs, '...If you render an image with a 2:1 aspect ratio and map it to
> a sphere using spherical mapping, it will recreate the scene!'
> 
> Secondly, if you're working with meshes, try using Steve Cox's UV Mapper:
> http://home.pb.net/~stevecox/uvmapper.htm
> 
> Gilles Tran has a very helpful tutorial for working with it here:
> http://www.mediaport.net/Artichaud/Tran/sources/tutuve.htm
> 
> Hope this helps...

Post a reply to this message

In article <39721EB9.554BD97C@yahoo.com>, ryan constantine 
<rco### [at] yahoocom> wrote:

> looking at the docs, i see that a cylindrical camera makes an image of
> the outside of the cylinder, which presumably has no radius.  what i
> would like to do is specify a radius (in order to envelope objects) and
> then create the image based on the inside of the cylinder.  this (i
> think) would have the effect of "unrolling" the object into two
> dimensions, ready to be used as a template for image maps, bumpmaps, or
> image pattern maps and could be rolled back onto the object using
> cylindical mapping.  this would eliminate the need to divide a model
> into two halves and then use planar image mapping as was done, for
> example, in h.e. day's raptor model.  a spherical cam that could also do
> this would be similarly useful.  would this be difficult to implement? 
> do others think this would be useful?

This sort of "inside-out" camera should be fairly easy to do...though I 
have never really looked at that portion of the code. I think an 
"inverse_spherical" camera would be more useful than the cylinderical 
version, since you could map the top and bottom at the same time as the 
front and sides.
It wouldn't work with all objects, for example, objects with holes 
running through them or parts overlapping each other, but it could be 
useful for many cases.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

Post a reply to this message

Chris Huff wrote:

> This sort of "inside-out" camera should be fairly easy to do...though I
> have never really looked at that portion of the code. I think an
> "inverse_spherical" camera would be more useful than the cylinderical
> version, since you could map the top and bottom at the same time as the
> front and sides.
> It wouldn't work with all objects, for example, objects with holes
> running through them or parts overlapping each other, but it could be
> useful for many cases.

How 'bout this: adding "inverse" to the camera would make it the corresponding
inverse type & if there is no corresponding type the POV would show a warning
- <camtype> cannot be inverted, using non-inverted camera.
I wonder how the images would look for these weird cams.
Also what about an object_cam - to find the initial ray points you might trace
from a point like the spherical cam and where those traces hit the object you
start tracing and the ray directions would be the surface normals at those
points.

--
Bye
Pabs

Post a reply to this message

I think that someone suggested something like this a long time ago. The
idea was the same, ie. adding an 'inverse' keyword to the camera. It would
make povray to take the farthest intersection of the camera ray with the
scene instead of the nearest. That is, instead of shooting the ray from
the camera to the infinity, the ray is kind of shot from infinity to the
camera, and the scene is thus seen from "outside".

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message

ryan constantine wrote:

>this (i
>think) would have the effect of "unrolling" the object into two
>dimensions,

Newsgroups: povray.binaries.images
Subject: Flat Cat  [~50 kB]
From: ing### [at] homenl (ingo)
Message-ID: <8EC9F6D80seed7@204.213.191.228>
Date: 28 Jan 2000 17:50:25 -0500

Is this the kind of picture you're looking for?


Ingo

-- 
Photography: http://members.home.nl/ingoogni/
Pov-Ray    : http://members.home.nl/seed7/

Post a reply to this message

but my idea included a radius, so the ray wouldn't come from infinity. 
the ray would be shot from one side of the cylinder and if it hit an
object, fine, but if not, it would stop when it hit the other side of
the cylinder, as if what was contained in the cylinder was all that
existed in the universe.

Warp wrote:
> 
>   I think that someone suggested something like this a long time ago. The
> idea was the same, ie. adding an 'inverse' keyword to the camera. It would
> make povray to take the farthest intersection of the camera ray with the
> scene instead of the nearest. That is, instead of shooting the ray from
> the camera to the infinity, the ray is kind of shot from infinity to the
> camera, and the scene is thus seen from "outside".
> 
> --
> main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
> ):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message

On 17 Jul 2000 09:26:02 -0400, Warp <war### [at] tagpovrayorg> wrote:

>  I think that someone suggested something like this a long time ago. The
>idea was the same, ie. adding an 'inverse' keyword to the camera. It would
>make povray to take the farthest intersection of the camera ray with the
>scene instead of the nearest. That is, instead of shooting the ray from
>the camera to the infinity, the ray is kind of shot from infinity to the
>camera, and the scene is thus seen from "outside".

But that would be slooow, especially with isosurfaces, text, CSG,
julias, polys etc. Shooting from 'infinity' to the camera is a better
idea, or even better, as already suggested, from a specified distance
to the camera (which would also eliminate precision problems)


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG      e-mail : pet### [at] tagpovrayorg

Post a reply to this message

Peter Popov <pet### [at] usanet> wrote:
: But that would be slooow, especially with isosurfaces, text, CSG,
: julias, polys etc.

  Why should it be any slower than the usual way?
  Don't tell me you think that it takes time for the ray to travel from
infinity to the scene? :)

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message