## rotation around y axis

Like all linear transformations that command is in 2 modes:
direct and matrix.

## roty obj

### roty(an)obj(id)

Rotates the object **id** angle **an** around y ayis versus
its center of gravity.
### roty(an) vertex(s) obj(id)

Rotates vertices **s** of the object **id** angle **an** around y axis
versus its center of gravity.
### roty(an) poi(x,y,z) obj(id)

Rotates the object **id** angle **an** around tth y axis versus point **(x,y,z)**.

**Note:**

objt is **fog, light, var, vol, view**.

**Exeamples:**

`roty(PI/2) poi(100,-20,50) vertex[1,5] vol(1,3);`

y rotates vertices
(1,2,3,4,5) of volumes 1 et 3 angle PI/2around point (100,-20,50).

`roty(PI/2) var("x");`

y rotates variable **x** angle PI/2
around its center of gravity.

`roty(.1*PI) eye view(1);`

angle .1*PI around y axis the eys of the view 1.
### roty(a1,a2)vol(a)roty(b1,b2)vol(b)

Varies **roty matrix vol(a)** in the interval **[a1,a2]** when
**roty matrix vol(b)** varies in the interval **[b1,b2]**.

May be used to attach **roty** variations
of volume **a** to those of its father **b**.

**Note:** **roty(b1,b2)** can be any other transformation **transf(b1,b2)**.
## roty image

### roty(an) image(id)

Makes identic first ligne and last ligne of the image **id**.

**Notes:**

1) **an** is ethe portion of the image (between 0 and PI) affected by this operation.

2) Blur appears in this portion.

3) Useful for mapping an image on a closed surface in y.

4) If identifier **id** is absent, the current image by default.

**Example:**

`roty(.1*PI) image(1);`

makes periodic the image by changing one tenth of its surface.
## rotx matrix

### roty matrix vol(id)

Returns the angle of rotation about y of the matrix of the volume **id**.

**Options:**

**format(f)**: modulo **f**.
### roty(a)matrix vol(id)

Rotates angle **a** around y the volume **id** by changing its matrix.

**Options:**

**ini**: the transformation is the basic.
## roty view

### roty(an)eye view(id)

Rotates the eye of the view **id** angle **an** around y axis.
### roty(an)aim view(id)

Rotates the aim point of the view **id** angle **an** around y axis.

**Options:**

**validate(0)**: rotationfrom the initial position.
## See also: