Alain <aze### [at] qwertyorg> wrote:

> > can someone explain to me some of the notation in the pov-ray help files. I
> > looked in the help for how to make a prism and it gave this:
> >
> > PRISM:
> >  { [PRISM_ITEMS] F_HEIGHT1, F_HEIGHT2, I_NUM_POINTS, POINT_LIST [open]
> > [PRISM_MODIFIERS] }
> F_HEIGHT1, F_HEIGHT2 determine the vertical extent of the prism. They
> must be different. Their use is very simple for linear_sweep. It can be
> tricky when you use a conical_sweep (normaly, you also need to use some
> scaling).
> I_NUM_POINTS is the number of points needed to define the shape of the
> prism. It includes the actual points plus any controll points.
> POINT_LIST is a list of the actual 2D doordinates of all the points
> defining the shape of the prism. It MUST match the value of I_NUM_POINTS.
>
> > PRISM_ITEMS:
> > [PRISM_SPLINE_TYPE] & [PRISM_SWEEP_TYPE]
> Those are optional parameters with default values.
>
> > PRISM_SPLINE_TYPE:
> > linear_spline | quadratic_spline | cubic_spline | bezier_spline
> linear_spline means that the points are connected by straight lines. NO
> controll point. (default spline type used if not defined)
> All others can have curved shapes and need at least 2 controll points.
> bezier_spline use: point, control_point, control_point, point,
> control_point,....(2 control points between each actual points pair)
>
> > PRISM_SWEEP_TYPE:
> > linear_sweep | conic_sweep
> linear = sides that are parallel (default value that will be used if you
> don't provide that parameter)
> conic = sides that converge to a single point.
> You must use one or the other, but never both.
>
> > PRISM_MODIFIERS:
> > [sturm [BOOL]] & [OBJECT_MODIFIERS]
> Optional parameters.
> strum use an alternate, more precise but slower, algorythm to trace the
> prism. If strum is absent, it's means "strun off". It's presence alone
> means "strum on".
> The object modifiers are things like rotation, scalling and
> translations. Can also include any pigment, texture or material.
>
> >
> > what do the F/I and in other areas V terms mean? I can't work out how to do a
> > prism from this information
> >
> > Please help
> >
> > Thanks
> >
> >
> "F" is for a float numerical value: 1.2345, pi, 1/3, sin(0.1), ...
> "I" is for an integer numerical value: 1
> "V" is for a vector like: <1,2>, <1,2,3>,... If needed, a single float
> or integer can be used if you want a vector where all elements have the
> same value. In that case, the value provided will be promoted to a
> vector. 1 can become <1,1,1>
>
> A simple prism:
> prism{0,1, 4 0,<1,1>,<1,0>,0}
> Create a triangular prism one unit high. The sides are straight and
> vertical.
>
>
> Alain



Thankyou for your help-thats brilliant.

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