Here are two questions that are connected:
1. In the POVRAY coordinate system at least one function is sensitive to the
direction "North" and that is "sunpos". Is North in the z-direction by
default?
2. If the answer to the first question is "yes", is there any global
rotation or setting possible to bring the north direction in say a
townscape to align with the z-axis?

Any help on this topic would be greatly appreciated. JLH

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JLH wrote:
> Here are two questions that are connected:
> 1. In the POVRAY coordinate system at least one function is sensitive to the
> direction "North" and that is "sunpos". Is North in the z-direction by
> default?

There is no such thing as "North" in POV-Ray. What are you talking about?

	Thorsten

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Thorsten Froehlich <tho### [at] trfde> wrote:
> JLH wrote:
> > Here are two questions that are connected:
> > 1. In the POVRAY coordinate system at least one function is sensitive to the
> > direction "North" and that is "sunpos". Is North in the z-direction by
> > default?
>
> There is no such thing as "North" in POV-Ray. What are you talking about?
>
>  Thorsten

"sunpos" requires an input of h:m:s, lat long, to provide the correct
direction of the sun's light. This requires an implicit assumption of the
direction of the N-S meridian. I was wanting to find out if this was the
z-axis. Since then I have found in the help files that the N-S line is
indeed the z axis. Now I just wonder at the answer to the second
question-can one do global rotations of whole scenes? I suspect the answer
is no. JLH

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JLH wrote:
> Thorsten Froehlich <tho### [at] trfde> wrote:
>> JLH wrote:
>>> Here are two questions that are connected:
>>> 1. In the POVRAY coordinate system at least one function is sensitive to the
>>> direction "North" and that is "sunpos". Is North in the z-direction by
>>> default?
>> There is no such thing as "North" in POV-Ray. What are you talking about?
>>
>>  Thorsten
> 
> "sunpos" requires an input of h:m:s, lat long, to provide the correct
> direction of the sun's light. This requires an implicit assumption of the
> direction of the N-S meridian. I was wanting to find out if this was the
> z-axis. Since then I have found in the help files that the N-S line is
> indeed the z axis. Now I just wonder at the answer to the second
> question-can one do global rotations of whole scenes? I suspect the answer
> is no. JLH

Well, the "sunpos" you seem to be talking about is nothing more than a
macro, so you can (a) see how it is implemented by checking "sunpos.inc" and
(b) it only returns a location vector. Consequently, there is little use to
rotate the whole scene to match to a light source which is *also* part of
that scene (nothing would change).

In short, what you want to do is translate the light source, not the scene.
As you can have as many consecutive translations as you want, this is
trivial to do.

	Thorsten

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JLH nous apporta ses lumieres en ce 2007/06/18 09:08:
  Thorsten
> 
> "sunpos" requires an input of h:m:s, lat long, to provide the correct
> direction of the sun's light. This requires an implicit assumption of the
> direction of the N-S meridian. I was wanting to find out if this was the
> z-axis. Since then I have found in the help files that the N-S line is
> indeed the z axis. Now I just wonder at the answer to the second
> question-can one do global rotations of whole scenes? I suspect the answer
> is no. JLH
> 
> 
You can do a global rotation of a whole scene. Here is how you do it:
Option 1: Wrap your whole scene, optionaly exepting the camera, in a global 
union. Rotate that union. If you want, you can leave out some or all of your 
light(s).
Option 2: Rotate the camera

-- 
Alain
-------------------------------------------------
   My wife is such a bad cook, in my house we pray after the meal.
   	Rodney Dangerfield

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Alain <ele### [at] netscapenet> wrote:
> JLH nous apporta ses lumieres en ce 2007/06/18 09:08:
>   Thorsten
> >
> > "sunpos" requires an input of h:m:s, lat long, to provide the correct
> > direction of the sun's light. This requires an implicit assumption of the
> > direction of the N-S meridian. I was wanting to find out if this was the
> > z-axis. Since then I have found in the help files that the N-S line is
> > indeed the z axis. Now I just wonder at the answer to the second
> > question-can one do global rotations of whole scenes? I suspect the answer
> > is no. JLH
> >
> >
> You can do a global rotation of a whole scene. Here is how you do it:
> Option 1: Wrap your whole scene, optionaly exepting the camera, in a global
> union. Rotate that union. If you want, you can leave out some or all of your
> light(s).
> Option 2: Rotate the camera
>
> --
> Alain
> -------------------------------------------------
>    My wife is such a bad cook, in my house we pray after the meal.
>     Rodney Dangerfield

Alain: Thank you for your reply. That is what I wanted. The reason for the
request is that architects and planners often use a "conventional" north in
their drawings so that the coordinates are simplest (i.e. North is taken
parallel to some street when in reality it is some angle away from north).
All is irrelevant until you are interested in the actual time resolution of
sun shadows, in which case the whole scene must be rotated wrt the sun to be
geographically correct. This is the situation I have at the moment. So there
is at least one operation in POVRAY that is
North dependent. JLH

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