Finally, textures are projected over and any sections of the model can be edited or replicated to produce variations or new objects, thus the object on the left produces a new objection on the right. Then the user starts defining a shape and showing the sweep direction along which the program monitors edges to determine width and direction. The program first takes an image and does edge object extraction. The extrusion does not need to be uniform or in a straight line – the assumptions are a valid cross sectional shape – related to the starting shape and a reasonable edge detection.Īs seen above there are several stages. The process works on producing a base shape a box or circle and then extruding it. But if one avoids such things and focuses on household objects, there is a huge range of complex models that this approach really solves quickly, from lamps to taps, from candle sticks to telescopes, they can all be modeled edited and textured with ease.
Hidden objects or obscured parts are nearly impossible to define. So too would images shot with large amounts of lens distortion – anything like a fisheye would confuse the assumptions of parallel lines. For example, a classic tapering tube of toothpaste starts as an extrusion of a circle and ends as a collapsed line. It is also easy to find examples that won’t work with this approach but to do this is only really useful in understanding how the technique works and the assumptions that are exploited. It is easy sometimes to only focus on the high end – but for many mobile or game applications and even previs – close enough done fast is often more than good enough.
While it is possible to immediately fault the model on close inspection, usually due to texture artifacts or non-responsive highlights or shading on rotation – the model is still quite passable for a number of great uses and it wins due to the sheer speed and simplicity of the process. It is not that this 3-Sweep process produces the best models ever, it is that it produces a passable model very, very easily. As most effects artist know, when you project a texture over a simple shape, the result can be quite appealing, even if the lighting is “baked in” and the back of the object is just a mirror of the front.
And once these shapes are defined the original texture projected onto the shapes is likely to give the appearance of quite a complex model. A cup is a cylinder which is just an extruded circle but then its handle is also likely to be able to be modeled also with a curved extruded oval. Many objects, especially man-made objects, are straight or have sensible curves and handles which themselves can be seen as extrusions. The technique succeeds by not trying to solve being able to model everything, but just doing certain things very, very easily. Motivated in great part by the difficulty in sharing models and even making models, a group of researchers including Tao Chen realized that if a user could direct the computer, and if the solution used a combination of edge detection with some fairly reasonable assumptions – coupled with some texture projections it would be possible to make 3D models very quickly and simply of a whole range of objects – especially man made objects.