Descriptions and Examples for the POV-Ray Raytracer by Friedrich A. Lohmüller Geometric Shapes in POV-Ray Italiano Français Deutsch

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- sor
> lathe
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- ovus

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# "lathe" = surface of revolution

"lathe"
- surface of revolution

general syntax:
 ```lathe{ Spline_Type n, < x1, y1 >, < x2, y2 >, < x3, y3 >, ... < xn, yn > texture{ ... } }```

Here "n" points < xi, yi >( i = 1 to n ) are used to define a outline of a body in the xy-plane. These points are conected by a spline curve. The body appears by a rotation of this line arround the y-axis.
By default this curve will not be closed ortogonally to the y-axis.
If we want to get a closed body we have to use as last point the first point. .
Sometimes errors occure by the limited caculating accuracy, shown by holes in the surface of revolution. By adding the statement "sturm" it is sometimes possibe to reduce them (this forces POV-Ray to use the slower but more accurate algorithm of Sturm when calculating square roots).

To get another position and/or orientation of the surface of revolution you have to use "rotate<  ,   ,   >" and "translate< , , >" .
Sample left:
 ```lathe{ quadratic_spline // Spline_Type 5, // number of points, <2, 0>, // points, <3, 0>, <3, 5>, <2, 5>, <2, 0> // sturm texture{ pigment{ color rgb<0.4,0.2,1>} finish { phong 1 reflection 0.2} } // end of texture scale<1,1,1>*1 rotate<0,0,0> translate<0,0.6,0> } // end of lathe object //-----------------------```

Hint: Why "sor" instead of "lathe" ?
(the last one seems most times to be more flexible!)
By calculating intersections with "sor"-objects quadratic equations are necessary, by intersection tests with "lathe"-objects you need to calculate with equations of the 6th order. Quadratic equations are much faster and accurate to solve! Because of such objects have many parts of surfaces this is very important!

 © Friedrich A. Lohmüller, 2010 www.f-lohmueller.de top