Preparing The Coloring Data For The Rapid Formation Of Surface Colored Models

Rapid Prototyping Technology has been progressing rapidly since it was first developed in the eighties of the 20th century. Colored models can give more information than mono-colored models, which make communication more convenient, faster, and more efficient. Forming colored models by Rapid Prototyping techniques has been the hope of the industry. In recent years, Color Rapid Prototyping attracts more and more attention. Some research projects on the process and equipment for forming colored models have already been done. Even commercial color rapid forming equipments have been developed.Most colored models are used only for visualization purpose. They need to be colored only in the surface or sectional regions. They are called surface colored models.A digital model must be created first in order to form a surface colored model, and be output in a proper format. Methods for modelling surface colored models and formats for describing these models were introduced. A new file format, the ESTL format, was proposed. It describes the geometry of a model in a similar way as STL format does, so it retains the feature of simplicity and ease of post processing which STL format has. Data redundancy has also been decreased by the use of a new format scheme. Its characteristic is also in the capability of describing complex surface texture of a model. It uses affine mapping from a rectangular texture image to each facet to describe simple texture mapping on a surface, and it describes complex texture mapping by simply store the result image of the complex texture mapping onto each facet. Though very simple, it can describe the complex surface detail of a model. So it is suited to be used as an intermediate format for describing surface colored models.The digital model must be sliced prior to fabrication. A method for slicing CAD models in Color STL or ESTL format was proposed. Different with the method for slicing a mono-colored model, it is actually a voxelization method. The principle is as follows. For slicing a layer, first calculate the intersection polygon of the layer and each facet, and scan the projection of Ihe polygon onto the XY plane to rapidly find the boundary voxels. For all the facet intersecting a boundary voxel, calculate the area of the intersection polygon of the boundary voxel and each of the facets, and find the maximum one. If the corresponding facet has only a simple color definition, then assign the voxel the same color as the facet. Otherwise the facet has a texture mapping definition, then the voxel is assigned a color equal to the average color of the polygonal region in texture space, which is mapped from the intersection of the voxel and the facet. Finally, the interior of the layer must be filled. This method has solved the problem of slicing CAD models in Color STL or ESTL format It is also meaningful to the development of the method for slicing CAD models in PLY or VRML format.In order to assure not baring the uncolored interior of a surface colored model after "subtractive" post processing, the colored regions of the model should be of a certain thickness. This requires that the colored regions in the volume dataset describing the slicing result of a...