T U T O R I A L

Splines

· The complete lower section of the »Tools-menu« is reserved for a special object called »Splines«. What exactly are splines ? A spline is a mathematical curve, based upon polynomal equations of different degrees, that is formed in accordance to the positions of a varying number of »control points.« Wow, sounds not too simple! OK, let's try it another way:

· Imagine a triangle where the corners are not connected (as shown in the picture to the left). Drawing a curve from point [1] through point [2] to point [3] results in the most simple spline, you can create.

· Let's pin down Fact No 1: a spline must have at least three control-points. Now imagine, that you move point [2]; how would this affect the shape of the curve. The following picture will give the answer ...

· Time for Fact No 2: - a movement of any control point of a spline affects the shape of the curve. POVLAB handles splines in the same way as described above - but there is more: a third dimension.


· In the pictures above the curve is just a 2D-line and has no thickness at all. Since we are creating 3D-objects, there has to be a possibility to set the thickness of a spline. Let's have an example-scene, to see how this can be achieved in POVLAB - click here to download the file »spltut01.zip« (700 Byte). 		Drawing the first spline

· If you want to draw the spline by yourself, do the following: Step 1 - create a new scene and maximize the front-view. Step 2 - from the »Tools-menu« choose the command »Create B-Spline« (you will then be asked to select a viewport to draw in; choose the front-view by clicking on it). Step 3 - move the crosshair- cursor to the postion [X=-2, Y=-1] (the Z- value is zero in the frontview anyway) and press the left mouse- button to insert the first control-point of the spline. Step 4 - insert the control-points 2 and 3 at the coordinates: (P2) [X=0, Y=1], (P3) [X=2, Y=-1]. Step 5 - after drawing the third point, press the right mouse-button to generate the B-Spline (POVLAB will ask you for an object-name). After this procedure you should have somthing like this ...




· As shown, we have three »sphere-like« shapes, which are the control points and a blue line between those points, representing the B-Spline itself.

(continued on next page)
Chapter B/Page 16
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This page was last modified on: 1996-08-09 		Mail to the author of the POVLAB-Tutorial:
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