Hi,

Is there any way to make a solid height_field, so that if you difference
from it (for example, a footprint), you would get an indent (unless you're
Ken), and not a hole.

If not, what is the best approach to this problem?

--
Tom Melly
tom### [at] tomandluforce9couk
http://www.tomandlu.force9.co.uk

Post a reply to this message

Tom Melly wrote:
> 
> Hi,
> 
> Is there any way to make a solid height_field, so that if you difference
> from it (for example, a footprint), you would get an indent (unless you're
> Ken), and not a hole.
> 
> If not, what is the best approach to this problem?

  Actualy the best approach is not trying to csg the HF in this case. I
would instead add the foot prints to the HF image itself.
  In other cases were you want to add something like a cave through the side
of a mountain it is possible with a little creative CSG work. I have done so
in the past using an intersection and a difference of a cylinder through the
HF object. It takes a little bit of thinking on how CSG works but it is not
impossible.

  difference{
  intersection{
    height_field{tga "kpeak1.tga" smooth translate <-.5,-0.431,-.5>
    scale <128, 72, 128>rotate y*270 pigment{ rgb 1 }finish{ambient .7}}
    cylinder{<0,0,-120>,<0,0,154>,10 inverse pigment{rgb 1} finish{ambient .7}}}
    cylinder{<0,0,-120>,<0,0,154>,10 open    pigment{rgb 1} finish{ambient .7}}}

This worked for me once when adding a see through cave in a mountain peak image
I was working on. Your milage may vary and will depend on the topography of the
HF you attempt to apply it to.

-- 
Ken Tyler -  1200+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

Post a reply to this message

On Sun, 7 Nov 1999 04:33:18 -0000, "Tom Melly" <tom### [at] tomandluf9couk>
wrote:

>Hi,
>
>Is there any way to make a solid height_field, so that if you difference
>from it (for example, a footprint), you would get an indent (unless you're
>Ken), and not a hole.
>
>If not, what is the best approach to this problem?

A height_field *is* solid -- it extends from its surface down to the
x-z plane. In the standard distro there's a demo scene called
"hf_clip.pov" or "hfclip.pov" or something like that which
demonstrated how to use this feature.


Peter Popov
ICQ: 15002700

Post a reply to this message

Peter Popov wrote:

> A height_field *is* solid -- it extends from its surface down to the
> x-z plane.

That is a bit misleading Peter. While HF's are solid from the point of
view that they may be used in CSG operations because pov can clearly
determine their inside and outside for all practical purposes they
are not really a solid object in as much as they are a triangle mesh
object that much more closely resembles a shell of an object and not
a solid object like a box or a sphere would be. You can verify this
yourself by making a HF object that looks like a mountain peak. If
you flip it over it will now look like a deep valley.

-- 
Ken Tyler -  1200+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

Post a reply to this message

Ken <tyl### [at] pacbellnet> wrote:
: That is a bit misleading Peter. While HF's are solid from the point of
: view that they may be used in CSG operations because pov can clearly
: determine their inside and outside for all practical purposes they
: are not really a solid object in as much as they are a triangle mesh
: object that much more closely resembles a shell of an object and not
: a solid object like a box or a sphere would be. You can verify this
: yourself by making a HF object that looks like a mountain peak. If
: you flip it over it will now look like a deep valley.

  Your answer is a bit misleading too. There are no solid objects in povray.
  Heightfields work with CSG as any other "solid" object.

  If you are worried about the heightfield being an open surface, you can
make it closed very easyly:

intersection
{ height_field { ... }
  box { 0,1 }
}

-- 
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

Nieminen Juha wrote:

>   Your answer is a bit misleading too. There are no solid objects in povray.
>   Heightfields work with CSG as any other "solid" object.

  I think I was quite a bit less misleading than Peter was but two wrongs
do not make a right so I stand corrected by your obvious greater knowlege
of such things. <yeah right>

-- 
Ken Tyler -  1200+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

Post a reply to this message

On Sun, 07 Nov 1999 05:07:44 -0800, Ken <tyl### [at] pacbellnet> wrote:

>
>
>Nieminen Juha wrote:
>
>>   Your answer is a bit misleading too. There are no solid objects in povray.
>>   Heightfields work with CSG as any other "solid" object.
>
>  I think I was quite a bit less misleading than Peter was but two wrongs
>do not make a right so I stand corrected by your obvious greater knowlege
>of such things. <yeah right>

That last remark ("<yeah right>") was a really rare example of
expressing disagreement by a double positive statement :)


Peter Popov
ICQ: 15002700

Post a reply to this message

Peter Popov wrote:

> That last remark ("<yeah right>") was a really rare example of
> expressing disagreement by a double positive statement :)

In English we would call that "dripping with sarcasm". :)

-- 
Ken Tyler -  1200+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

Post a reply to this message

Peter Popov <pet### [at] usanet> wrote:
: That last remark ("<yeah right>") was a really rare example of
: expressing disagreement by a double positive statement :)

  If Ken expressed disagreement, that means that he thinks there are solid
objects in povray. I don't think so.

-- 
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 Sun, 07 Nov 1999 00:45:33 -0800, Ken wrote:
>
>
>Peter Popov wrote:
>
>> A height_field *is* solid -- it extends from its surface down to the
>> x-z plane.
>
>That is a bit misleading Peter. While HF's are solid from the point of
>view that they may be used in CSG operations because pov can clearly
>determine their inside and outside for all practical purposes they
>are not really a solid object in as much as they are a triangle mesh
>object that much more closely resembles a shell of an object and not
>a solid object like a box or a sphere would be.

Wow, that's a long sentence.  AIs must not need to breathe. :)

No, what's misleading is that he gave the wrong bounds for the thing.
A point is "inside" a height field if its Y coordinate is less than
the Y coordinate of the height field at that X,Z location.  That is,
the inside extends from the surface to the X-Z plane, and all the way
along the -Y axis.  Try intersecting one with various size boxes to 
see this for yourself.

A height field is no more and no less solid than an "open" cylinder
or a clipped object.  It can do weird things with interiors like IOR
and media, but it works in CSG.  Contrariwise, there are objects that
are solid in how they work with interiors but don't work in CSGs: 
closed meshes and closed unions of patch objects both fit this criterion.
The word "solid" is hopelessly confusing to a POV user, so I try to 
avoid it altogether.

-- 
These are my opinions.  I do NOT speak for the POV-Team.
The superpatch: http://www2.fwi.com/~parkerr/superpatch/
My other stuff: http://www2.fwi.com/~parkerr/traces.html

Post a reply to this message