FreeForm Modeling and Surfacing
Modelers often throw up their hands and say, “If I could only touch the data inside the computer; if I could only use my hands.” The SensAble Technologies FreeForm modeling system addresses this concern. This system uses a specialized piece of hardware that has a haptic interface. Haptics is the aspect of FreeForm's user interface design that uses force-feedback to create the impression that the modeler is sculpting with his or her hands on a model inside the computer.

Technology like this would not have been possible a few years ago. Faster graphics cards and faster processors have allowed this software and hardware combination to create amazing 3D forms in the computer.

The data that is created by this device is similar to scan data. When exported into other packages, the data consists of thousands of small triangles that make up the data set. There are a couple notable distinctions, however. One distinction is that the data that is exported is very clean. Another distinction is the position of the data is right on the construction coordinates used for the digital modeling process.

The reason the data is extremely clean is that the data that is exported is a polygonal representation of a theoretical volume within the FreeForm software. The data-base that is calculated within FreeForm uses voxels to determine the volume of the object. Voxels are theoretical bits of 3D information that make up a 3D scene in a similar way that pixels fill up the 2D screen on the computer. These voxels contain information about the 3D sculpture in the FreeForm program. Some of this information includes the coarseness of the object, the shape of the object and the color of the object. (Coarseness is the hardness of the model.) Because voxels are true 3D entities, the sculptures created in FreeForm can be painted through the object. These colors on the object cannot be exported as texture maps, but they can be exported as colored point data on the surface of the object.

The coarseness of the sculpture in FreeForm is a very important aspect to using this program. Coarseness values correspond to the size of the voxels. Large voxels have a large coarseness value. If the virtual clay that is being sculpted has a very large coarseness value, the clay is very soft and can be easily sculpted. Soft clay, however, will not hold detail very well. As the sculpting continues, the hardness of the clay must be increased to get additional detail. Hardening the clay means reducing the size of the voxels. When the sculpture is finished, the clay will normally not be very coarse. The model shown in Figure 27 was built using the following steps:

1. Use an orthographic drawing or photograph to create a background image or image plane in FreeForm.

2. Make a large solid shape with a large coarseness size.

3. Make a curve on the front face of the shape that is used to cut the profile. Cut the profile with this curve.

4. Make a curve on the top to cut the top profile and cut the top profile with that curve.

5. Round off the edges, creating the basic 3D form of the sculpture.

6. Decrease the coarseness one step and add detail.

7. Decrease the coarseness another step and add more detail. Continue adding detail until the sculpture is complete (Figure 26).

8. Create surfaces on the model using curves and surfaces available in the surfacing toolbox.

9. Export the NURBS surfaces into the animation program.

[Figures 26 & 27] SensAble Technologies’ FreeForm system enables the modeler to create models using an intuitive sculpting tool and enables the export of NURBS patch models. Dinosaur model by Tom Capizzi; Demon model courtesy of C.H. Wang

The FreeForm modeling process differs from other methods of creating 3D models because it can create models with random complexity (Figure 27), and texture and graphics can be created in 3D, unlike most other modeling packages.

Another benefit to the system is that it has a built-in NURBS surfacing program, making it a fully functional stand-alone model creation package. The NURBS surfacing package is very intuitive and reliable and the NURBS surfaces that are exported from FreeForm are very clean. The NURBS surfacing software is not as flexible as the Paraform software, but it provides about 85% of the functionality and a fantastic sculpting package as well.