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Hi all,
I have a scene that renders correctly at 1000 x 1000 with this true
orthographic camera:
camera { orthographic
location <-28, -14.5, -28> * 1000
right 1000 * x
up 1000 * y
look_at <0, 0, 0> }
I'm now trying to create new 100 x 100 sub-portions of this scene. For
example, if I render at 100 x 100 using this camera:
camera { orthographic
location <-28, -14.5, -28> * 1000
right 100 * x
up 100 * y
look_at <0, 0, 0> }
I get a 100 x 100 image that's *identical* to the (450, 450) to (550, 550)
center of the original 1000 x 1000 image, which is perfect. But how can I
generalize this to render any portion of the scene? For example, how can I
generate a 100 x 100 image centered on the (30, 400) portion of the
original?
I think I can translate the camera and look_at point, doing something like:
camera { orthographic
#declare dx = ?;
#declare dy = ?;
#declare dz = ?;
location (<-28, -14.5, -28> * 1000) + <dx, dy, dz>
right 100 * x
up 100 * y
look_at <dx, dy, dz> }
I just can't wrap my head around the math required to calculate dx, dy & dz,
given a center pixel location of (30, 400). Any advice?
A little more background: the scene is in a predefined pov file with no
camera. I'm generating new pov files programmatically; these simply
include the original scene and a dynamically calculated camera (based on
user input).
Thanks in advance!
Remi
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Le 17.09.2007 20:32, remigagne nous fit lire :
> Hi all,
>
> I have a scene that renders correctly at 1000 x 1000 with this true
> orthographic camera:
>
> camera { orthographic
> location <-28, -14.5, -28> * 1000
> right 1000 * x
> up 1000 * y
> look_at <0, 0, 0> }
>
> I'm now trying to create new 100 x 100 sub-portions of this scene. For
> example, if I render at 100 x 100 using this camera:
>
> camera { orthographic
> location <-28, -14.5, -28> * 1000
> right 100 * x
> up 100 * y
> look_at <0, 0, 0> }
>
> I get a 100 x 100 image that's *identical* to the (450, 450) to (550, 550)
> center of the original 1000 x 1000 image, which is perfect. But how can I
> generalize this to render any portion of the scene? For example, how can I
> generate a 100 x 100 image centered on the (30, 400) portion of the
> original?
>
> I think I can translate the camera and look_at point, doing something like:
>
> camera { orthographic
> #declare dx = ?;
> #declare dy = ?;
> #declare dz = ?;
> location (<-28, -14.5, -28> * 1000) + <dx, dy, dz>
> right 100 * x
> up 100 * y
> look_at <dx, dy, dz> }
>
> I just can't wrap my head around the math required to calculate dx, dy & dz,
> given a center pixel location of (30, 400). Any advice?
>
Notice that direction here is originally as +z.
Therefore, dz = 0.
And you should simplify your orthographic camera by remplacing the
look_at with direction.
If dx=dy=0 give you a center at (500,500) of the big one, the new
camera will be centered on 500+dx,500+dy.
So, if you want the center at (XX,YY), dx = XX-500 and dy = YY-500.
(30,400) -->>>> dx = -470, dy = -100.
--
The superior man understands what is right;
the inferior man understands what will sell.
-- Confucius
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> I'm now trying to create new 100 x 100 sub-portions of this scene. For
> example, if I render at 100 x 100 using this camera:
POV has command line options for partially rendering a scene.
(3.1.2.2.2 Partial Output Options)
Also in the windows version you can drag a box onto the render
window to partially render a portion of your image.
This doesn't crop the images for you though, so it might not be
what you want.
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remigagne nous apporta ses lumieres en ce 2007/09/17 14:32:
> Hi all,
>
> I have a scene that renders correctly at 1000 x 1000 with this true
> orthographic camera:
>
> camera { orthographic
> location <-28, -14.5, -28> * 1000
> right 1000 * x
> up 1000 * y
> look_at <0, 0, 0> }
>
> I'm now trying to create new 100 x 100 sub-portions of this scene. For
> example, if I render at 100 x 100 using this camera:
>
> camera { orthographic
> location <-28, -14.5, -28> * 1000
> right 100 * x
> up 100 * y
> look_at <0, 0, 0> }
>
> I get a 100 x 100 image that's *identical* to the (450, 450) to (550, 550)
> center of the original 1000 x 1000 image, which is perfect. But how can I
> generalize this to render any portion of the scene? For example, how can I
> generate a 100 x 100 image centered on the (30, 400) portion of the
> original?
>
> I think I can translate the camera and look_at point, doing something like:
>
> camera { orthographic
> #declare dx = ?;
> #declare dy = ?;
> #declare dz = ?;
> location (<-28, -14.5, -28> * 1000) + <dx, dy, dz>
> right 100 * x
> up 100 * y
> look_at <dx, dy, dz> }
>
> I just can't wrap my head around the math required to calculate dx, dy & dz,
> given a center pixel location of (30, 400). Any advice?
>
> A little more background: the scene is in a predefined pov file with no
> camera. I'm generating new pov files programmatically; these simply
> include the original scene and a dynamically calculated camera (based on
> user input).
>
> Thanks in advance!
>
>
> Remi
>
>
>
It would be easier if your camera was parallel to an axis, like the z axis.
You first need to evaluate how many pov-units fit in your 1000 original pixels.
It can be evaluated empiricaly using a plane with a checker pattern. It can be
calculated from the direction vector that default to 1. It's about the same as
the distance between the location and the look_at point, or about 42169
pov-units whide! The field of view extend 0.5 units left and right from the
camera axis at 1 unit in front of the camera, multiplied by the distance to the
look_at point.
So, for each 1 pixel of movement, you need to move the camera 42.17 units. You
could use the vrotate(<Udx,Udy,0>, Your_Angle) macro on the <Udx, Udy, 0> vector
of the user to get the <dx,dy,dz> translate vector you need.
You can add translate<dx,dy,dz> to your camera after everything else. This way,
your camera won't change it's orientation: the location and look_at will change
in exactly the same direction and distance. Easier to maintain and less chance
of making a typo.
--
Alain
-------------------------------------------------
You know you've been raytracing too long when you have ever "Hand-Coded" a
bezier patch.
Stephan Ahonen
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Sorry for the delayed response, but I just got everything working. Thanks
so much for all your feedback!
The hint that hit it home was the simple observation that everything is
easier with a camera parallel to axis. So, instead of positioning my
camera to get the right view angle, I left it looking straight down the Z
axis, then rotated the entire scene itself. Seems strange, but it worked
like a charm!
Also, if the image is 100x100 and orthographic camera up=100*y and
right=100*x, translating the camera that looks down z by one unit in either
x or y gives exactly a one pixel difference in output. Wonderful!
Thanks again for all the help.
Remi
Alain <ele### [at] netscape net> wrote:
> It would be easier if your camera was parallel to an axis, like the z axis.
> You first need to evaluate how many pov-units fit in your 1000 original pixels.
> It can be evaluated empiricaly using a plane with a checker pattern. It can be
> calculated from the direction vector that default to 1. It's about the same as
> the distance between the location and the look_at point, or about 42169
> pov-units whide! The field of view extend 0.5 units left and right from the
> camera axis at 1 unit in front of the camera, multiplied by the distance to the
> look_at point.
> So, for each 1 pixel of movement, you need to move the camera 42.17 units. You
> could use the vrotate(<Udx,Udy,0>, Your_Angle) macro on the <Udx, Udy, 0> vector
> of the user to get the <dx,dy,dz> translate vector you need.
> You can add translate<dx,dy,dz> to your camera after everything else. This way,
> your camera won't change it's orientation: the location and look_at will change
> in exactly the same direction and distance. Easier to maintain and less chance
> of making a typo.
>
> --
> Alain
> -------------------------------------------------
> You know you've been raytracing too long when you have ever "Hand-Coded" a
> bezier patch.
> Stephan Ahonen
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