###### Descriptions and Examples for the POV-Ray Raytracerby Friedrich A. Lohmüller About Loops with POV-Ray
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- POV-Ray Tutorial

Loops in POV-Ray
1. For + While
Comparison
2. Linear
Transformations
3. Circular
Transformations
4. Moebius etc.
5. Screws
& Spirals
6. Twisting
Spirals
>7. Snails
& Ammonites
8. Spherical Spirals 1
9. Spherical Spirals 2
10. Fibonacci Spirals

## Loops for Snails and Ammonites

In the last exsamples of a spiral the spheres had always the same size. Now we will see how to reduce continually the size of the spheres, the radius and the height of the screwing of a snail:

 ```//------------------------------------- #declare Ball = sphere{<0,0,0>,0.5 texture{pigment{color rgb<1,0.65,0.0>} finish {phong 1}}} #declare Radius0=3.0;// basic radius #declare NR=9;//number of revolutions #declare NpR=100;//number elements p.r. #declare Scale=0.75; //per revolution #declare HpR=0.8;//difference in y p.r. //------------------------------------- #local Hd = HpR/NpR; #local Scale_p = pow(Scale,1/360); #local Scale_pE = pow(Scale_p,360/NpR); #local Old_S = Scale_pE; #local Old_H = Hd; #declare Nr = 0; //start #declare EndNr = NR*NpR; // end #while (Nr< EndNr) object{Ball translate scale Old_S translate<0,Old_H,0> rotate<0,Nr*360/NpR,0>} #declare Nr = Nr+1; // next Nr #declare Old_S =Scale_pE*Old_S; #declare Old_H =Old_H+Hd*Old_S; #end // ------------ end of loop -----```
Scene file for POV-Ray: povloopa.pov
or: povloopa.txt

If we reduce the height of the screwing to zero,
we get the classic form of
"Ammonitus povrayensis":

 ```//----------------------------------- #declare Ball = sphere{<0,0,0>,1.0 texture{...see above...}}} #declare Radius0 = 3.5; #declare NR = 9;//number of revolutions #declare NpR=50;//number of elem.p.r. #declare Scale = 0.55; //per revolution #declare HpR = 0.00; //------------------------------------```
Scene file for POV-Ray: povloopb.pov
or: povloopb.txt

By scaling the shape of the basic element and texturing it with stone or granit textures it is possible to form nearly every shape of a snailhouse or ammonite you wish: For example: what about a
"Turritella turris var. povensis"?

 ```//--------------------------------- #declare Ball = sphere{<0,0,0>,0.70 scale <1,1.5,1> texture{T_Stone3 scale 1.5 finish {phong 0.3}}} #declare Radius0 = 1.5; #declare NR=9.1; //number of revolutions #declare NpR = 30; //number of elements per revolution #declare Scale=0.78; //per revolution #declare HpR = 1.6; //---------------------------------```
Scene file for POV-Ray: povloopc.pov or: povloopc.txt

 Overview | For + While | Linear | Circular | Moebius | Screws+Spirals | Twisted Spirals | Snails | Spherical 1 | Spherical 2 | Fibonacci |
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 © Friedrich A. Lohmüller, 2014 http://www.f-lohmueller.de