Thanks for the effort of making the "isosurface" documents.
I have a comment on the last paragraph of 9.1.2.8.

>Note that there are certain patological[pathological?] functions 
>where no max_gradient [or accuracy] will help, no matter how big. 
>These are usually functions with many sharp angles (ie. not 
>differentiable), discontinuities or similar "ill-behaving" 
>properties. With those you just have to find a solution which gives 
>the best quality/speed tradeoff. Isosurfaces work best with 
>functions which give smooth surfaces. 

I made the isosurface code not only for smooth surfaces but also 
for surfaces with sharp edges or rough surfaces.  
It's possible to render sharp edge surfaces if we use appropriate 
(differentiable) functions and (accuracy and max_gradient) parameters.  
I will post an example in p.b.i.

Thus, the second sentence of above paragraph should be like this "These 
functions usually have discontinuities (i.e. not differentiable)." 

BTW, has someone in POV-Team checked the 'bilinear' function in image.c?
(See http://news.povray.org/3bdf97e6@news.povray.org )
Maybe the interpolation bug was not so important for the previous 
version but it is severe for isosurfaces with 'image_map' because it 
generates discontinuities.

R. Suzuki

Post a reply to this message

R. Suzuki <r-s### [at] aistgojp> wrote:
: Thus, the second sentence of above paragraph should be like this "These 
: functions usually have discontinuities (i.e. not differentiable)." 

  Ok, I'll change that. However, the comment in the parentheses should then
also be changed (or even removed). A curve or surface can be continuous, but
still not differentiable at a certain point. This usually means that there's
a sharp point or edge there.

-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

Post a reply to this message

"Warp" <war### [at] tagpovrayorg> wrote
>: Thus, the second sentence of above paragraph should be like this "These
>: functions usually have discontinuities (i.e. not differentiable)."
>
>  Ok, I'll change that. However, the comment in the parentheses should then
>also be changed (or even removed). A curve or surface can be continuous,
but
>still not differentiable at a certain point. This usually means that
there's
>a sharp point or edge there.

Yes. The comment in the parentheses should be removed,
or "not differentiable" should be changed to "infinite gradient".
# I have not checked my message well before the posting. Sorry.

R. Suzuki

Post a reply to this message