Sven Littkowski <jam### [at] yahoocom> wrote:
> Kenneth,
>
> using your code, I am able to project the image into the shape of a
> cylinder. But I cannot put my green pigment on it, it remains in its
> gray colors (like the original image). How to change that?

That's odd. I DO see the green color, using just your code example. Did you
combine the 'MyLandscape' object with some other CSG and then apply another
different 'gray' texture?
>
> I have the thread "The Colony Ship" inside the "Images" section here,
> and could upload the images there. But here is the code:
>

Yes, post an image there.

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"Kenneth" <kdw### [at] gmailcom> wrote:

>
> Unlike a regular height_field, the image_map eats INTO the cylinder (but with
> the correct 'positive' grayscale height values.) For example, if your image_map
> has white values that are 1.0 in brightness, that part of the corresponding
> cylindrical heightfield will by at the outer radius of the cylinder surface;
> darker image colors will eat *into* the cylinder.
>

Actually, that's only half-true (which has just become clear to me-- and I've
been working with the HF_Cylinder macro for years!)

As the 'depth' value in the macro increases, the radius of the entire
height_field cylinder ALSO increases (but not the *length* of the cylinder)--
you end up with a 'fatter' cylinder, which actually distorts the 3D image_map
pattern. The pattern looks stretched-out horizontally. (You can see this by
setting 'depth' to an extreme .99.)

IDEALLY, as 'depth' increases, the cylinder should stay at the same radius, with
the image_map function simply 'eating into' it. But that's not what happens.

I'm working on some SCALE equations to compensate for this, but it's...
complicated. The first thing to do is to scale up the *length* of the cylinder,
to get the embossed pattern to look undistorted again. Then the entire cylinder
needs to be scaled *down*, to get it back to its original radius and length.

The tricky thing about this is that it all depends on the particular 'depth'
value used.

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Am 14.02.2016 um 21:01 schrieb Kenneth:

> As the 'depth' value in the macro increases, the radius of the entire
> height_field cylinder ALSO increases (but not the *length* of the cylinder)--
> you end up with a 'fatter' cylinder, which actually distorts the 3D image_map
> pattern. The pattern looks stretched-out horizontally. (You can see this by
> setting 'depth' to an extreme .99.)
> 
> IDEALLY, as 'depth' increases, the cylinder should stay at the same radius, with
> the image_map function simply 'eating into' it. But that's not what happens.

That wouldn't be ideal either, as it would /reduce/ the effective radius
of the entire height_field cylinder on average, creating the opposite
distorting effect.

The fact is that there is no ideal solution (because there is no telling
what the average height of your image_map function is), and whoever
implemented HF_Cylinder just picked this particular implementation for
other properties.

The primary reason may have been that a corresponding behaviour in
HF_Sphere makes it easy to use for modeling planets, with the nominal
radius specifying sea level and everything else being raised above it.

> I'm working on some SCALE equations to compensate for this, but it's...
> complicated. The first thing to do is to scale up the *length* of the cylinder,
> to get the embossed pattern to look undistorted again. Then the entire cylinder
> needs to be scaled *down*, to get it back to its original radius and length.
> 
> The tricky thing about this is that it all depends on the particular 'depth'
> value used.

Maybe the easiest way to approach this is to simply adjust the nominal
radius parameter as you change the depth parameter.

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clipka <ano### [at] anonymousorg> wrote:
> Am 14.02.2016 um 21:01 schrieb Kenneth:
>

> >
> > IDEALLY, as 'depth' increases, the cylinder should stay at the same radius,
> > with the image_map function simply 'eating into' it. But that's not what
> > happens.
>
> That wouldn't be ideal either, as it would /reduce/ the effective radius
> of the entire height_field cylinder on average, creating the opposite
> distorting effect.
>

I was assuming (probably incorrectly) that the image_map itself would always
have *some* pure white areas in it-- which would equate to the max height of the
HF (meaning, the max radius of the HF_Cylinder.) It's that max radius I was
referring to. In experiments I'm doing with two really odd (and dynamic) scaling
equations, I can *almost* get that max radius AND height to stay at set values,
no matter what the 'depth' value. But "almost" isn't quite good enough yet...
:-/

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Seeing all these problems, I am wondering, if there is a possibility in
POV-Ray, to twist a given OBJECT to become a cylinder.

If that function does not exist yet, here is a suggestion:
1
That function needs to twist an object of any dimension, example:
that object is not 1 unit tall, but lets say 10 units (imagine a box)
2
When twisting to a cylinder, there is no standard size (of 1 unit), but
the radius is set by the user, this way, a cylinder-twisted object with
a height of 10 units would not lead to a cylinder that is fully filled,
if the cylinder radius was set to let's say 100 units. Also, the user
can set the begin and end radius, that enables cylinders and also funnels.

Here my vision:

/*
The object ("MyObject) must be centered by the user at < 0, 0, 0 > and
the lowest point (Z axis) must be 0, while the highest point is open
(any number). The user cares about that by using the proper radius. The
OBJ_Cylinder function creates a cylinder from let's say -X to +X, the
radius from -Z to +Z.

Here, MyObject is assumed to range
from <-10.0, 0.0, -5.0> to <10.0, 10.0, 5.0>
*/

#declare TheLandscape = object
{
 OBJ_Cylinder(object { MyObject }, // the object to be twisted
                             10.0, // X (X Expanse of object)
                              5.0, // Z (Z Expanse)
                            100.0, // Cylinder Radius Begin
                             90.0, // Cylinder Radius End
  )
 rotate < 90.0, 0.0, 0.0 >  // any common object modifiers)
}

-------------------------------------------------------

On 14.02.2016 16:42, Kenneth wrote:
> clipka <ano### [at] anonymousorg> wrote:
>> Am 14.02.2016 um 21:01 schrieb Kenneth:
>>
> 
>>>
>>> IDEALLY, as 'depth' increases, the cylinder should stay at the same radius,
>>> with the image_map function simply 'eating into' it. But that's not what
>>> happens.
>>
>> That wouldn't be ideal either, as it would /reduce/ the effective radius
>> of the entire height_field cylinder on average, creating the opposite
>> distorting effect.
>>
> 
> I was assuming (probably incorrectly) that the image_map itself would always
> have *some* pure white areas in it-- which would equate to the max height of the
> HF (meaning, the max radius of the HF_Cylinder.) It's that max radius I was
> referring to. In experiments I'm doing with two really odd (and dynamic) scaling
> equations, I can *almost* get that max radius AND height to stay at set values,
> no matter what the 'depth' value. But "almost" isn't quite good enough yet...
> :-/
> 
> 
>

Post a reply to this message

On 2/15/2016 6:20 AM, Sven Littkowski wrote:
> Seeing all these problems, I am wondering, if there is a possibility in
> POV-Ray, to twist a given OBJECT to become a cylinder.
>
> If that function does not exist yet, here is a suggestion:
> 1
> That function needs to twist an object of any dimension, example:
> that object is not 1 unit tall, but lets say 10 units (imagine a box)
> 2
> When twisting to a cylinder, there is no standard size (of 1 unit), but
> the radius is set by the user, this way, a cylinder-twisted object with
> a height of 10 units would not lead to a cylinder that is fully filled,
> if the cylinder radius was set to let's say 100 units. Also, the user
> can set the begin and end radius, that enables cylinders and also funnels.
>
> Here my vision:
>
> /*
> The object ("MyObject) must be centered by the user at < 0, 0, 0 > and
> the lowest point (Z axis) must be 0, while the highest point is open
> (any number). The user cares about that by using the proper radius. The
> OBJ_Cylinder function creates a cylinder from let's say -X to +X, the
> radius from -Z to +Z.
>
> Here, MyObject is assumed to range
> from <-10.0, 0.0, -5.0> to <10.0, 10.0, 5.0>
> */
>
> #declare TheLandscape = object
> {
>   OBJ_Cylinder(object { MyObject }, // the object to be twisted
>                               10.0, // X (X Expanse of object)
>                                5.0, // Z (Z Expanse)
>                              100.0, // Cylinder Radius Begin
>                               90.0, // Cylinder Radius End
>    )
>   rotate < 90.0, 0.0, 0.0 >  // any common object modifiers)
> }
>
> -------------------------------------------------------
>
> On 14.02.2016 16:42, Kenneth wrote:
>> clipka <ano### [at] anonymousorg> wrote:
>>> Am 14.02.2016 um 21:01 schrieb Kenneth:
>>>
>>
>>>>
>>>> IDEALLY, as 'depth' increases, the cylinder should stay at the same radius,
>>>> with the image_map function simply 'eating into' it. But that's not what
>>>> happens.
>>>
>>> That wouldn't be ideal either, as it would /reduce/ the effective radius
>>> of the entire height_field cylinder on average, creating the opposite
>>> distorting effect.
>>>
>>
>> I was assuming (probably incorrectly) that the image_map itself would always
>> have *some* pure white areas in it-- which would equate to the max height of the
>> HF (meaning, the max radius of the HF_Cylinder.) It's that max radius I was
>> referring to. In experiments I'm doing with two really odd (and dynamic) scaling
>> equations, I can *almost* get that max radius AND height to stay at set values,
>> no matter what the 'depth' value. But "almost" isn't quite good enough yet...
>> :-/
>>
>>
>>

Maybe this will help.

http://www.reocities.com/SiliconValley/Lakes/1434/bend.html

I've never used it.


Mike

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Am 15.02.2016 um 12:20 schrieb Sven Littkowski:
> Seeing all these problems, I am wondering, if there is a possibility in
> POV-Ray, to twist a given OBJECT to become a cylinder.

Nope. Not with arbitrary objects.

> If that function does not exist yet, here is a suggestion:

Forget it. With most shapes, you'd need to convert them to something
more generic first, meshes being the most obvious choice.

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On 2/15/2016 11:32 AM, Mike Horvath wrote:
>
> http://www.reocities.com/SiliconValley/Lakes/1434/bend.html
>
> I've never used it.
>
>
> Mike

Are these links all written down anywhere (like in the wiki)? Or is it 
just individual bookmarks.

Years ago, someone had a blob tutorial (Jaime or Warp?) that I'd like to 
find.

dik

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I saw it, just recently. The URL was given to me inside one of my
threads here, where I asked about water media.

On 15.02.2016 17:30, dick balaska wrote:
> Years ago, someone had a blob tutorial (Jaime or Warp?) that I'd like to
> find.

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Somewhere inside my "Wanted: Air and Water" thread, inside the GENERAL
section of this newsgroup.

On 15.02.2016 17:30, dick balaska wrote:
> Years ago, someone had a blob tutorial (Jaime or Warp?) that I'd like to
> find.

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