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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<head>

<!--

.style1 {font-size: x-large}

.style2 {font-size: xx-large}

-->

</style>

<!--

function MM_jumpMenu(targ,selObj,restore){ //v3.0

eval(targ+".location='"+selObj.options[selObj.selectedIndex].value+"'");

if (restore) selObj.selectedIndex=0;

}

//-->

</script>

</head>

<body>

<tr>

If you're new to Python

and VPython: <a href="VisualIntro.html">Introduction</a>

A VPython <a href="VPython_Intro.pdf" target="_blank">tutorial</a>

<a href="primitives.html">Pictures</a> of 3D objects

Choose an object:

<option>Choose an object</option>

<option value="cylinder.html">Overview</option>

<option value="arrow.html">arrow</option>

<option value="convex.html">convex</option>

<option value="curve.html">curve</option>

<option value="cylinder.html">cylinder</option>

<option value="ellipsoid.html">ellipsoid</option>

<option value="extrusion.html">extrusion</option>

<option value="faces.html">faces</option>

<option value="frame.html">frame</option>

<option value="helix.html">helix</option>

<option value="label.html">label</option>

<option value="lights.html">lights</option>

<option value="points.html">points</option>

<option value="pyramid.html">pyramid</option>

<option value="sphere.html">sphere</option>

</select>

Work with objects:

<option>Choose an option</option>

<option value="color.html">Color/Opacity</option>

<option value="materials.html">Materials/Textures</option>

<option value="shapes.html">Shapes Library</option>

<option value="paths.html">Paths Library</option>

<option value="defaults.html">Defaults</option>

<option value="rate.html">Animation Speed</option>

<option value="rotation.html">Rotations</option>

<option value="options.html">Additional Options</option>

<option value="delete.html">Delete an Object</option>

<option value="controls.html">Buttons/Sliders</option>

<option value="graph.html">Graphs</option>

<option value="lights.html">Lighting</option>

<option value="files.html">Read/Write Files</option>

<option value="trail.html">Leaving a Trail</option>

<option value="vector.html">Vector Operations </option>

<option value="factorial.html">factorial/combin</option>

</select>

Windows &amp Events:

<option>Choose a topic</option>

<option value="display.html">Windows</option>

<option value="mouse.html">Mouse Events</option>

<option value="mouse_click.html">   Mouse Click</option>

<option value="mouse_drag.html">   Mouse Drag</option>

<option value="keyboard.html">Keyboard Events</option>

</select>

What's new in <a href="new_features.html">Visual 5</a>

<a href="http://vpython.org" target="_blank">VPython web site</a>

<a href="license.txt" target="_blank">Visual license</a>

<a href="http://www.python.org" target="_blank">Python web site</a>

<a href="http://www.python.org/doc/2.5.2/lib/module-math.html" target="_blank">Math module</a> (sqrt etc.)

<a href="http://www.scipy.org/Documentation" target="_blank">Numpy module</a> (arrays) </td>

<div>

<tr>

</tr>

</table>

</div>

<div>

In the first diagram we show a simple example of a box object:<img src="VisualRef-6.gif" alt="box" align="right" />

<div>

mybox = box(pos=(x0,y0,z0), length=L, height=H, width=W)

The given position is in the center of the box, at (x0,

y0, z0). This is different from cylinder, whose pos attribute is at one

end of the cylinder. Just as with a cylinder, we can refer to the individual

vector components of the box as mybox.x, mybox.y, and mybox.z.

The length (along the x axis) is L , the height (along the y axis) is H

, and the width is W (along the z axis). For this box, we have mybox.axis

= (L, 0, 0) . Note that the axis of a box is just like the axis of

a cylinder.

For a box that isn't aligned with the coordinate axes, additional issues come into play. The orientation of the length of the box is given by the axis (see second diagram):

</div>

<div>

mybox = box(pos=(x0,y0,z0),     axis=(a,b,c), length=L,

height=H, width=W)

The axis attribute gives a direction for the length of the box, and the length, height, and width of the box are given as before (if a length attribute is not given, the length is set to the magnitude of the axis vector).

There remains the issue of how to orient the box rotationally

around the specified axis. The rule that Visual uses is to orient the width

to lie in a plane perpendicular to the display "up" direction,

which by default is the y axis. Therefore in the diagram you see that the

width lies parallel to the x-z plane. The height of the box is oriented

perpendicular to the width, and to the specified axis of the box. It helps

to think of length initially as going along the x axis, height along the

y axis, and width along the z axis, and when the axis is tipped the width

stays in the x-z plane.

You can rotate the box around its own axis by changing which way is "up" for the box, by specifying an up attribute for the box that is different from the up vector of the coordinate system:

</div>

<div>

mybox = box(pos=(x0,y0,z0), axis=(a,b,c), length=L,

height=H, width=W, up=(q,r,s))

With this statement, the width of the box will lie in a plane perpendicular to the (q,r,s) vector, and the height of the box will be perpendicular to the width and to the (a,b,c) vector.

The box object has the following attributes and

default values, like those for cylinders: pos (0,0,0), x (0), y(0), z(0), axis (1,0,0), length (1), color (1,1,1)

which is color.white, red (1), green (1), blue (1),

opacity (1), <a href="materials.html">material</a>, and up (0,1,0).

Additional box attributes:

height In the y direction

in the simple case, default is 1

width In the z direction

in the simple case, default is 1

size (length, height,

width), default is (1,1,1)

mybox.size=(20,10,12) sets length=20, height=10,

width=12

Note that the pos attribute

for cylinder, arrow, cone, and pyramid corresponds to one end of the object,

whereas for a box, sphere, or ring it corresponds to the center of the object.

If you include make_trail=True when you create the object, a trail will be left behind the object as you move it. For related options, see <a href="trail.html">Leaving a Trail</a>.

See description of <a href="options.html">Additional

Attributes</a> available for all 3D display objects.

</div>

</td>

</tr>

<tr>

</tr>

</table>

</body>

</html>

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