Scilab Function

geom3d - projection from 3D on 2D after a 3D plot

### Calling Sequence

  `[x,y]=geom3d(x1,y1,z1)`

### Parameters

- `x1,y1,z1` : real vectors of the same size (points in 3D).
- `x,y` : real vectors of the same size as `x1`, `y1` and `z1`.

### Description

After having used a 3D plot function such as `plot3d`, `plot3d1` or `param3d`, `geom3d` gives the mapping between a point in 3D space `(x1(i),y1(i),z1(i))` and the corresponding point `(x(i),y(i))` in the projected 2D plan. Then all the 2D graphics primitives working on `(x,y)` can be used for superposition on the 3D plot.

### Examples

    deff("[z]=surf(x,y)","z=sin(x)*cos(y)")
    t=%pi*(-10:10)/10;
    // 3D plot of the surface
    fplot3d(t,t,surf,35,45,"X@Y@Z")
    // now (t,t,sin(t).*cos(t)) is a curve on the surface
    // which can be drawn using geom3d and xpoly
    [x,y]=geom3d(t,t,sin(t).*cos(t));
    xpoly(x,y,"lines")
    // adding a comment
    [x,y]=geom3d([0,0],[0,0],[5,0]);
    xsegs(x,y)
    xstring(x(1),y(1),"point (0,0,0)")

### Author

J.Ph.C.