POV-Ray : Newsgroups : povray.newusers : Odd transformation of cylinders Server Time: 27 Nov 2020 17:10:50 GMT
 Odd transformation of cylinders (Message 1 to 6 of 6)
 From: Cyningstan Subject: Odd transformation of cylinders Date: 11 Aug 2020 05:35:00 Message:
```I'm not "new" to POV-Ray but returning to it after a number of years. But this
problem I've run into is definitely in newbie territory.

I'm building up a basic scene currently using only spheres and cylinders. The
spheres are acting as I'd expect, but the cylinders are having an odd
transformation applied to them that I have to undo. They're all being rotated
-45 degrees around the X axis, and translated down by whatever their radius is.
For example:

camera {
location <0, 0, -10>
look_at  <0, 0,  0>
}

cylinder {
<0 0 -1.25>
<0 0 1.25>
1
}

This isn't the full scene; I've omitted lighting and textures for brevity. I'd
expect to be looking at this cylinder end-on, but it's actually rotated -45
degrees and moved down -1, so I'm looking at the top side. I have to bring it
back to where I expect with the following:

rotate <+45 0 0>
translate <0 0 +1>

My 0.5 radius cylinders need translating up +0.5 on the Z axis, and all
cylinders need a +45 degree correction on the X axis.

Neither the tutorial nor the reference section on the cylinder give me any clue
as to why this weird transformation is being applied to all my cylinders, and I
don't remember having this problem last time I built a scene about seven years
ago. Is there something obvious I'm missing?

Thanks!
```
 From: Thomas de Groot Subject: Re: Odd transformation of cylinders Date: 11 Aug 2020 06:38:25 Message: <5f323ce1@news.povray.org>
```Op 11/08/2020 om 07:30 schreef Cyningstan:
>
> For example:
>
> camera {
>    location <0, 0, -10>
>    look_at  <0, 0,  0>
> }
>
> cylinder {
>    <0 0 -1.25>
>    <0 0 1.25>
>    1
> }

Not sure if this is the cause, but I am missing the ",". To be
unambiguous, you should write:

cylinder {
<0, 0, -1.25>,
<0, 0, 1.25>,
1
}

>
> This isn't the full scene; I've omitted lighting and textures for brevity. I'd
> expect to be looking at this cylinder end-on, but it's actually rotated -45
> degrees and moved down -1, so I'm looking at the top side. I have to bring it
> back to where I expect with the following:
>
>    rotate <+45 0 0>
>    translate <0 0 +1>

Same here:

rotate <45, 0, 0>
translate <0, 0, 1>

>
> My 0.5 radius cylinders need translating up +0.5 on the Z axis, and all
> cylinders need a +45 degree correction on the X axis.
>
> Neither the tutorial nor the reference section on the cylinder give me any clue
> as to why this weird transformation is being applied to all my cylinders, and I
> don't remember having this problem last time I built a scene about seven years
> ago. Is there something obvious I'm missing?
>
> Thanks!
>
>

--
Thomas
```
 From: Cyningstan Subject: Re: Odd transformation of cylinders Date: 11 Aug 2020 08:20:01 Message:
```Thomas de Groot <tho### [at] degrootorg> wrote:

> Not sure if this is the cause, but I am missing the ",". To be
> unambiguous, you should write:

Thanks, Thomas! You're absolutely right, it was the missing commas. I made the
mistake in one place and then copied and adapted it all over the place without
noticing.
```
 From: Thomas de Groot Subject: Re: Odd transformation of cylinders Date: 11 Aug 2020 08:30:37 Message: <5f32572d@news.povray.org>
```Op 11/08/2020 om 10:18 schreef Cyningstan:
>
> Thomas de Groot <tho### [at] degrootorg> wrote:
>
>> Not sure if this is the cause, but I am missing the ",". To be
>> unambiguous, you should write:
>
> Thanks, Thomas! You're absolutely right, it was the missing commas. I made the
> mistake in one place and then copied and adapted it all over the place without
> noticing.
>
>

Excellent! I have a dim memory of an explanation some time ago by Alain
Martel about /why/ omitting the commas is ambiguous. I cannot find it
presently.

--
Thomas
```
 From: Alain Martel Subject: Re: Odd transformation of cylinders Date: 11 Aug 2020 16:23:45 Message: <5f32c611\$1@news.povray.org>
```Le 2020-08-11 Ã  01:30, Cyningstan a Ã©critÂ :
>
> I'm not "new" to POV-Ray but returning to it after a number of years. But this
> problem I've run into is definitely in newbie territory.
>
> I'm building up a basic scene currently using only spheres and cylinders. The
> spheres are acting as I'd expect, but the cylinders are having an odd
> transformation applied to them that I have to undo. They're all being rotated
> -45 degrees around the X axis, and translated down by whatever their radius is.
> For example:

> cylinder {
>    <0 0 -1.25>
>    <0 0 1.25>
>    1
> }
>

This get interpreted as :
cylinder{<0, 0-1.25> <0,0,1.25> 1}

You can ignore the comas, but only in unambiguous cases. Whenever you
have a negative value, the coma is mandatory in front of it.

There was a time, prior to version 3.0, where the space was a hard
separator and when your way of defining the vector was interpreted as
<0,0,-1.25>. It's been over 30 years that it's no longer the case.
```
 From: Leroy Subject: Re: Odd transformation of cylinders Date: 16 Aug 2020 17:35:00 Message:
```We've all done something like this at one time or another.
Those commas hide sometimes!

Have fun!
```