In article <396A7DDA.970C6F5A@online.no>, Tor Olav Kristensen 
<tor### [at] onlineno> wrote:

> As I understand from the documentation, trace() can not provide the 
> initial points to "shoot" vectors from.

It doesn't...how would it know where you want to look?


> Nor can it provide the directions in which to point the vectors so 
> that they point towards the blob surface. (Or is there available a 
> "field direction" function in MegaPOV ?)

There is not, though it wouldn't be too difficult to figure out with a 
macro and eval_pattern().


> For complex blob shapes it will not be enough to "shoot" several 
> vectors from a circle centre towards the circle surface (nor from the 
> surface towards the centre).
> 
> But my macros can make use of trace() to find the exact positions of 
> the blob surface once it knows all the points to "shoot" from and in 
> which direction to "shoot" the vectors.

One possible way of doing it would be to trace() in a 3D grid, 
continuing on after each intersection on the same line. This wouldn't 
provide a very even coverage, though...actually, it would probably give 
something like the image you posted.
You might also trace in random directions from the center of each 
component. This wouldn't work for every blob, but it should produce some 
interesting results.


> I agree. This sounds like a faster way to determine the "file 
> strength" at a point.

You mean "field strength"? :-)
It could also take a blob object which has already been defined, if you 
are using the latest version of my MegaPOVPlus blob pattern patch(which 
is available at my web site and probably will be in the next MegaPOV).


> I haven't read anything about vtransform() yet. 
> Is it a MegaPOV feature ?

Yes. It just takes a transformation and a vector, and returns the 
transformed vector. Sort of like vrotate(), but can also be used with 
scale, translate, matrix, and complex combinations of these(and also 
declared transforms).

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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