Voxel

In computer graphics, the term refers to voxel (composed of volumetric and pixel ) one grid point ( " image " point, data element ) in a three-dimensional grid (not raster graphics ). This corresponds to a pixel in a 2D image, a raster graphics. Usually the position as pixels is not explicitly stored in voxels but implicitly derived from the position to other voxels. In contrast, the positions of the coordinates of the corners are stored at points or polygons. A direct consequence of this difference is that you can represent a 3D structure with a lot of empty or homogeneously filled space efficiently with polygons. Voxel on the other hand are good at equidistantly sampled representation of a space that is not filled homogeneously.

Description

Voxel means two things:

The spatial data

In a three-dimensional data record which is present in discretized form in Cartesian coordinates, called the discrete voxel value in a XYZ - coordinate of the data set. In this definition it is the three-dimensional equivalent of a pixel, thus, a voxel has no definite shape. We speak here also of the isotropic voxel or " volume pixel". These are often at the data contained in Voxelgittern to color values ​​that are determined by the means of volume rendering for visualization. Applications is this form of data representation, especially in the imaging process of the medicine, here, the discrete values ​​are considered as the density (bone, adipose tissues) and visualized accordingly.

For the presentation of these voxels, there are specialized algorithms. The marching cubes algorithm allows converting voxel data in polygon. However, this requires a threshold value, since the polygons are not usually transparent. Another method is a direct rendering of the voxel data. This can be done with ray casting by casting a ray through the voxel and calculated the color values ​​. Canceled, if opacity is achieved.

Raytracing

In other cases, a voxel refers to a cell within a rectangular parallelepiped or a regular divided unlimited space. Most commonly this meaning is used with certain techniques to accelerate ray tracing. Since this method is, however, does not adapt to the local conditions not very efficient. It is better to use an acceleration structure such as the kd - tree.

Use

Usually voxels are used in medicine or in the representation of landscapes in computer games and simulation. ( Heightmap ) is Voxelterrain instead of a height field used because it may represent overhangs, caves, arches and other 3D features of a landscape. These concave features can with a height field can not be represented because it stores only the top level of the landscape, and everything underneath assumed to be filled.

Computer Games

• Voxelspace: technology developed by the company NovaLogic game engine for various war simulations.
• C4 Engine: game engine, the voxels used to represent the terrain. There are editing a Voxeleditor within the level editor.
• Command & Conquer: Tiberian Sun and Red Alert 2 used it to display vehicles.
• Crysis: Uses a combination of height field and voxels for its terrain system.
• Outcast: A Game of Belgian developer Appeal, which renders the outer landscapes with a voxel engine.
• Voxelstein 3D voxel used to enable a fully destructible environment.
• Castle story
• Comanche: An early implementation of Voxeltechnik, which itself can be used on computers of 80386'er generation.

Voxeleditoren

While scientific volumetric representation does not require any modification of the actual voxel data, there are Voxeleditoren with which one can create models for voxel-based games. Some of these editors are focused on a single way to edit the voxel, while others mix different methods.