> What bothers me more is that when viewed at close range, all 
> heightfields inevitably look "blocky", so I ask myself whether it is 
> possible to convert the height value matrix of a heightfield by 
> "cross-approximating" each row and column into a discrete 3D function 
> like it is used with isosurfaces...

what you can also try is to superimpose random detail from
f_ridged or similar onto a handcrafted lower resolution HF.
Suppose you have some 2048x2048 HF data, but enough free
memory so you could render a much higher resolution.

You can then

1. Define a pigment P based on the HF image_map
2. Define a pigment function FP based on P.gray
3. Define a random detail funtion FR (e.g., f_ridged)
4. Define a terrain function such as 0.9*FP + 0.1*FR
5. Create HF from function image at desired resolution

Of course it's still blocky, but maybe less so.

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"scott" <sco### [at] scottcom> schreef in bericht 
news:493e3cb6$1@news.povray.org...
>
> Did you consider using the "bicubic_patch" object in POV?  Maybe you could 
> find (or write) some code to convert each heightfield cell into a bicubic 
> patch, this would then still look very smooth even if you got very close.
>
>
A program like GeoControl does something like that I think as it has the 
possibility to export the heightfield as an .obj file. The other side of the 
medal however, is that this file is HUGE, a few hundreds of MB for a high 
resolution heightfield. This is very difficult to manage subsequently and I 
am unsure about its render possibilities in terms of memory. I never could 
go beyond the export process... :-(

Thomas

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Jörg 'Yadgar' Bleimann nous illumina en ce 2008-12-09 06:58 -->
> High!
> 
> SharkD schrieb:
> 
>> Have you tried using the "smooth" statement in heightfields?
> 
> I did, but I would like to go for REAL smooth surfaces, not just 
> "cosmetic" normal tricks!
> 
> See you in Khyberspace!
> 
> Yadgar
You can use a hight_field for the far parts, and cover it with some 
bicubic_patch for the close by area.

-- 
Alain
-------------------------------------------------
I find that the harder I work, the more luck I seem to have.
Thomas Jefferson

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Very nice. Wonder if you could do an Albert Bierstadt painting with that 
method?

Mike


"Jaime Vives Piqueres" <jai### [at] ignoranciaorg> wrote in message 
news:493e5d6d$1@news.povray.org...

>> Does anyone here know about such POV macros/external programs to do this 
>> job?
>
> Here are my experiments on that matter:
>
> http://www.ignorancia.org/en/index.php?page=Heightfield_based_Isosurfaces
>
> Indeed, it is an interesting method, but very slow with radiosity (not to 
> talk about media... ;).
>
> Regards,
>
> --
> Jaime

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Mike Williams <nos### [at] econymdemoncouk> wrote:

> I suspect that isosurface spline functions might possibly do the job.
>
> The basic strategy would be for a grid to be laid over the heightfield,
> and for the edges of each square to be sampled to produce four splines.
> Each square patch could then be rendered...

The first thing that popped into my mind, as I read the poster's question, was
very similar to your idea, but only as a sort of vague concept of how it
*might* be accomplished.  But going from concept to code is another matter, and
I dismissed the idea as too outlandish and 'out there.' Glad to see that I
wasn't crazy after all! :-)

Ken W.

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Jaime Vives Piqueres wrote:

> 
>> Does anyone here know about such POV macros/external programs to do 
>> this job?
> 
> 
> Here are my experiments on that matter:
> 
> http://www.ignorancia.org/en/index.php?page=Heightfield_based_Isosurfaces
> 
> Indeed, it is an interesting method, but very slow with radiosity (not 
> to talk about media... ;).
> 
> Regards,
> 
> -- 
> Jaime

The image, /hf2iso-070424-1.jpg

for me goes beyond merely a 'realistic' portrayal of rocks.  It actually 
conjures memories of the sublime confrontation of landscape I 
experienced as a boy canoeing in Northern Ontario.

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Jaime Vives Piqueres schrieb:


> 
>> Does anyone here know about such POV macros/external programs to do 
>> this job?
> 
> 
> Here are my experiments on that matter:
> 
> http://www.ignorancia.org/en/index.php?page=Heightfield_based_Isosurf
aces

Looks nice - note you could spare the separate preprocessing steps by 
using the function image type (combined with the gradient calculation 
functions for the slope map)

Concerning the original question:  Use of the bicubic interpolation from 

MegaPOV generally improves the appearance of image based isosurfaces up 
to the point where you at least don't see the grid structure any more. 
And concerning the interpolation of height contours into a regular grid 
- i found that most methods available for this purpose fail miserably 
when dealing with useful grid sizes (i.e. 3000 pixels squared or more). 
  A technique i found to work quite well can be found on: 
http://www.imagico.de/pov/earth_interpolate.html

-- Christoph

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>> Did you consider using the "bicubic_patch" object in POV?  Maybe you 
>> could find (or write) some code to convert each heightfield cell into a 
>> bicubic patch, this would then still look very smooth even if you got 
>> very close.
>>
> A program like GeoControl does something like that I think as it has the 
> possibility to export the heightfield as an .obj file. The other side of 
> the medal however, is that this file is HUGE, a few hundreds of MB for a 
> high resolution heightfield.

Yeh I guess even if you reduce the resolution by a factor of 2 or 4, it will 
be hard to beat the 2 bytes per point you need for the raw heightfield.

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Oh! Excellent! I shall have to experiment with your method indeed. I think 
that my GeoControl heightfields will do great with this.

Thomas

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=?ISO-8859-1?Q?J=F6rg_=27Yadgar=27_Bleimann?= <yaz### [at] gmxde> wrote:
> High!
>
> SharkD schrieb:
>
> > Have you tried using the "smooth" statement in heightfields?
>
> I did, but I would like to go for REAL smooth surfaces, not just
> "cosmetic" normal tricks!
>
> See you in Khyberspace!
>
> Yadgar

Wow! Stupid me, I thought POV did actual surface subdivision in this case.

-Mike

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