MATLAB Function Reference |

**Syntax**

**Description**

```
viewmtx
```

computes a 4-by-4 orthographic or perspective transformation matrix that projects four-dimensional homogeneous vectors onto a two-dimensional view surface (e.g., your computer screen).

```
T = viewmtx(az,el)
```

returns an *orthographic* transformation matrix corresponding to azimuth `az`

and elevation `el`

. `az`

is the azimuth (i.e., horizontal rotation) of the viewpoint in degrees. `el`

is the elevation of the viewpoint in degrees. This returns the same matrix as the commands

but does not change the current view.

```
T = viewmtx(az,el,phi)
```

returns a *perspective* transformation matrix. `phi`

is the perspective viewing angle in degrees. `phi`

is the subtended view angle of the normalized plot cube (in degrees) and controls the amount of perspective distortion.

Phi |
Description |

0 degrees |
Orthographic projection |

10 degrees |
Similar to telephoto lens |

25 degrees |
Similar to normal lens |

60 degrees |
Similar to wide-angle lens |

You can use the matrix returned to set the view transformation with `view(T)`

. The 4-by-4 perspective transformation matrix transforms four-dimensional homogeneous vectors into unnormalized vectors of the form (*x*,*y*,*z*,*w*), where *w* is not equal to 1. The *x*- and *y*-components of the normalized vector (*x/w*,* *y/w,* *z/w, 1) are the desired two-dimensional components (see example below).

```
T = viewmtx(az,el,phi,xc)
```

returns the perspective transformation matrix using `xc`

as the target point within the normalized plot cube (i.e., the camera is looking at the point `xc`

). `xc`

is the target point that is the center of the view. You specify the point as a three-element vector, `xc = [xc,yc,zc]`

, in the interval [0,1]. The default value is `xc = [0,0,0]`

.

**Remarks**

A four-dimensional homogenous vector is formed by appending a 1 to the corresponding three-dimensional vector. For example, `[x,y,z,1]`

is the four-dimensional vector corresponding to the three-dimensional point `[x,y,z]`

.

**Examples**

Determine the projected two-dimensional vector corresponding to the three-dimensional point (0.5,0.0,-3.0) using the default view direction. Note that the point is a column vector.

Vectors that trace the edges of a unit cube are

x = [0 1 1 0 0 0 1 1 0 0 1 1 1 1 0 0]; y = [0 0 1 1 0 0 0 1 1 0 0 0 1 1 1 1]; z = [0 0 0 0 0 1 1 1 1 1 1 0 0 1 1 0];

Transform the points in these vectors to the screen, then plot the object.

A = viewmtx(-37.5,30); [m,n] = size(x); x4d = [x(:),y(:),z(:),ones(m*n,1)]'; x2d = A*x4d; x2 = zeros(m,n); y2 = zeros(m,n); x2(:) = x2d(1,:); y2(:) = x2d(2,:); plot(x2,y2)

Use a perspective transformation with a 25 degree viewing angle:

A = viewmtx(

`-37.5,30,25`

); x4d = [.5 0 -3 1]'; x2d = A*x4d; x2d = x2d(1:2)/x2d(4) % Normalize x2d = 0.1777 -1.8858

Transform the cube vectors to the screen and plot the object:

A = viewmtx(-37.5,30,25); [m,n] =

`size`

(x); x4d = [x(:),y(:),z(:),`ones`

(m*n,1)]'; x2d = A*x4d; x2 =`zeros`

(m,n); y2 = zeros(m,n); x2(:) = x2d(1,:)./x2d(4,:); y2(:) = x2d(2,:)./x2d(4,:);`plot`

(x2,y2)

**See Also**

Controlling the Camera Viewpoint for related functions

Defining the View for more information on viewing concepts and techniques

view | volumebounds |

© 1994-2005 The MathWorks, Inc.