You are presented a four dimensional scene, containing some objects
(on the main screen).
(If you are not familiar with 4D concepts, please read first the
introduction at the end.)
Every action in the object control can also be performed by keystroke, the concept is as follows:
With the 4 fingers of the left hand you control the objects and with the 4 fingers of the right hand you control the cameras. Normally the left 4 fingers are placed at a,s,d,f and the right 4 fingers are placed at j,k,l,; (on a US keyboard). Each finger is responsible for one 4 dimensional direction:
So pressing the corresponding finger moves the selected object along the specified axis. Pressing shift provides for moving in the opposite direction. The row on the keyboard above the just described middle row is responsible for 4 dimensional rotation. The fingers on the left hand rest on the keys q,w,r,t and the fingers on the right hand rest on the keys u,i,o,p. Each 4D rotation can be specified by two axes determining the rotation plane. The rotation is about moving the first axis to the second axis. In the same way you specify the rotation with your 4 fingers. For example first pressing the pointing finger (r), holding and pressing the small finger (q) provides for a rotation of the selected object from x to w.
For the not so extraordinary operating you can also use the cursor keys for moving the objects: left-right for x-axis, down-up for the y-axis, shift down-up for the z-axis and shift left-right for the w-axis. There is also the possibility to rotate the camera with the cursor keys by holding ctrl. The remaining keys are as follows:
We use the following view model: There is a 4D scene and a 4D camera. The 4D camera projects the 4D scene to its 3D film/projection area. Depending on the viewing mode this 3D area is recreated behind your screen from the viewpoint of a 3D (stereo) camera.
Generally the left mouse button is for rotation and the right mouse button for translation. Drag the mouse with the respectively pressed button and you will see the results. Left mouse button with shift is zoom.
You have perhaps already noticed that in the camera3/4d control panels two 2-axis elements are underlined. Per default xz and yw is underlined on the 4d camera control panel and xz and yz on the 3d camera control panel. The first underlined element corresponds to the rotation when dragging the mouse left-right and the second corresponds to the rotation that is performed when dragging the mouse down-up. Whether rotation of the 3d or 4d camera is performed depends on the corresponding switch. Also you can adjust there whether you mean rotation regarding the space axis (sys) or regarding the camera axes (cam).
For shifting the camera similarly two axes in the camera control panels are selected. The translation along the first selected axis corresponds again to the left-right movement of the mouse and the second selected axis corresponds to the down-up movement of the mouse.
Per default the red/cyan mode is presented to you, if you have no red/cyan glasses, choose another mode via the "view" menu. The following modes are available to you.
Note that you should use the adjustment screen to get an optimal viewing experience. You should size the 1cm or 1" square to that size (by operating the vertical and horizontal screen resolution).
There are some different methods how to map 3D objects to a pictorial. Most of them have 4D counterparts.
One drawback of the perspective projection is that we cannot easily conclude the real lengths due to the depth shortening. Of course no projection can preserve all lengths but it is already of much help to preserve the lengths (or at least the ratio to the original) parallel to the axes of the coordinate system, especially for rectangular shapes as in technical drawing or (this) computer game. Those projections are called axonometric projections (for further information see here).
To achieve this, one first defines the image of the trihedral on the picture
(i.e. three vectors u,v,w attached to a point o).
Then every point with the coordinates (x,y,z) is mapped
to the point o+x*u+y*v+z*w on the picture.
This is the same as if we apply the 2x3 matrix (u,v,w)
to the vector (x,y,z)T plus o, i.e. it
is equivalent to being an affine transformation from 3D to 2D.
Each axonometric projection has a viewing axis, that is the axis
mapped to o. Depending on the length ratio of the u,v,w
one categorizes the axonometric projection into isometric, dimetric and trimetric
projections. Typical used axonometric projections are
(we give ratios between the length of u,v,w and the
angles from (0,1) to u,v,w):
| 30° Isometric Perspective | isometric | 1:1:1 | 30°/90°/150° |
| Military Perspective | isometric | 1:1:1 | 45°/90°/135° |
| Cavalier Perspective | dimetric | 2:2:1 | 0°/90°/45° |
| Chinese Perspective | dimetric | 2:2:1 | 0°/90°/30° |
On the other hand we have parallel projections and orthogonal projections. Parallel projection: (parallel) rays mapping the object to the canvas. Orthogonal projection: The rays hit the canvas perpendicular.
When asking which axonometric projections is useful for four dimensions,
we note that (except for scaling) the 30° isometric perspective is the only one that is a
orthogonal projection (with the eye looking from (1,1,1) to (0,0,0)).
And the cavalier perspective is the only one that leaves
all except the last axis untouched and the last
axis has the same angle to each other axis in the image.
(Though this is true for the military projection with the y-axis too.)
Both descriptions can easily be extended to n dimensions.
And so we do to 4 dimensions (while we always use perspective projection for 3D).
The axonometric projections all use a fixed viewing angle so 4D rotation is disabled with them.
For a really recommendable introduction look at the 4D Visualization Page. As a starting point have also a look at Wikipedia's 4th dimension. There is also a great educational movie about 4 dimensional space. The rest of this chapter is only a quick patch introduction.
In opposite to the most spread idea of the time being the 4th dimension we consider here a truly 4 dimensional space, that is with 4 orthogonal space axes. Of course in our physical space we cannot put 4 axes together so that each is orthogonal to each other. On a paper we similarely can not draw 3 orthogonal lines but anyway most pictures show 3 dimensional content. Maybe a four dimensional beeing uses its pictures (i.e. 3 dimensional cuboids) to depict 4 dimensional content. And so we will do.
The four dimensional space is the straight forward generalization of the movement from 0 to 1 to 2 to 3 dimensions. So most questions for 4 dimensions can be answered when looking at the relation of the 2 (flatland) and 3 dimensional (our physical) space. Let us clarify the following questions:
There are useful other resources in the web to learn about 4D. You may want to have a look at (Sorted more or less from introductory to advanced):