Architecture. After such extensive destruction, we had limited information on the garden's architecture despite the availability of blueprint pieces. Since Chinese classical architecture has distinct styles, each style has strict rules that architects must follow. Traditionally, given less than five parameters of a building, an architect would derive the rest of the details based on the rules. For example, the door's size can be derived from the pillar's diameter. Given the known parameters of each architecture, we followed the same set of rules for the digital reconstruction.
Another challenge was the size of data for each architecture. Each Chinese classical architecture has hundreds of roof tiles and the same number of wood beams below the roof. Even using instances instead of copies, these tiles and beams still more than triple the architecture's data size. It would be nice if Alias|Wavefront had a good displacement map algorithm to create them using texture mapping instead of real geometry ( Figure 5).
Landscape. For the digital models, we measured the garden sites one by one. Many building and pillar bases still exist and offer accurate data about the size and shape of each building. Satellite and aerial survey data, combined with on-site measurement and description material, provide close-to-original data on the landscape.
Interior furnishings. Yuan Ming Yuan contained millions of pieces of decorative furniture. Most were intricate and detailed. We spent much time modeling these objects because we didn't want to lose the most important part—the details. With good 2D paint and texture-mapping tools, we were able to create some impressive art objects to furnish Yuan Ming Yuan ( Figure 6).
We could have used 3D scanners to scan some existing objects for texture and geometry. However, then we would have difficulty reconstructing them in a way that would look comparable.
Human figures and clothes. We experienced great difficulty in character modeling and animation. Realistic human models have always been on the front edge of computer graphics research and remain a difficult problem to solve. Realistic facial modeling and expressions are even more difficult to achieve.
Emperors and empresses in Yuan Ming Yuan wore costumes with detailed texture and patterns that matched their status. Human models wore the costumes during the animation process. However, this proved difficult because when the model changed positions, the position of the clothes shifted ( Figure 7).
Plants, trees, flowers. As you might expect, a Chinese garden has plants, trees, and flowers everywhere. Not only are they outdoors, but many are also put indoors as bonsai. Based on research, we estimated that Yuan Ming Yuan featured at least 500 types of plants in the garden—some rare, some even artificial—including hemp, a favorite ground cover. Botanical accuracy was of course necessary, and many of the trunks, leaves, and flowers had complex shapes.
Many software packages specialize in plant modeling, and some of them produce impressive results. Przemyslaw Prusinkiewicz is well known for the software he developed based on L-systems to model plants and trees. He and his colleagues provided the software (and training) for our project. Its modeling power is good, but our main problem was its data size—a single tree could be as large as 10 Mbytes in DXF format. Another problem is texture mapping, which can't be done in Studio because the plant data is polygonal. Polygonal leaves are copies of each other instead of instances. During camera movement, geometry data is not automatically simplified. All these problems prevented us from modeling plants effectively and efficiently.
Tai Lake rocks. Many Chinese gardens feature miniature mountains and caves made of rocks from Tai Lake in Southern China. These rocks have been eroded by the lake water for hundreds of years. They have thousands of holes of various sizes and are often of beautiful shapes.
Tai Lake rocks are complicated both topologically and geometrically. Modeling a Tai Lake rock proved challenging, because we tried to model a specific appearance and often a specific rock, but at the same time we wanted to achieve a natural look.
Therefore, we developed our own models. We designed and modeled the rock's overall shape in Studio using parametric spline surfaces. Then we scanned the shape and converted it onto a 3D grid. The grid size was chosen as a function of the level of details to be achieved for the resulting rock. Then spheres modeled the holes (actually, they can be modeled by any volume that can be scan-converted, but spheres suffice). These spheres were subtracted from the overall shape by a constructive solid geometry operation. The result was an object defined in a volumetric grid. We then tessellated the object into polygons and imported it into Studio.
Figure 8 shows the digital rock (right) next to a picture of a real rock we used for the overall shape (left). In the example, the model has about 3,000 triangles and topological holes. When rendering, we applied a fractal 3D texture to the surface to make it appear more realistic. To create different types of rocks, we changed the shape and distribution of the holes procedurally.
Water. Water is a key element of a Chinese garden. From the Sea of Fortune, the Yuan Ming Yuan's central body of water, to the hundreds of ponds, streams, and waterfalls, water covers more than half the garden. It plays a static role (as a reflecting surface) as well as a dynamic role in streams, currents, and falls. The main modeling challenge was including the dynamics of water. For example, when a boat runs through the water, the waves and splashes it produces are difficult to create by hand. These effects require physics-based modeling systems that the Studio software doesn't currently support.
Even though good models for waves, wakes, and moving water exist, we faced the problem of incorporating them together with the 3D models created in Studio. Therefore, we have not yet included them in the Yuan Ming Yuan model.