5.7. Tutorial: Modelling a part of an object

Problem

For a complex object that you may wish to animate, it can be helpful to build a separate textured 3D model of a single part of the object. This can also result in improved modelling accuracy.

Solution

3DSOM Pro allows you to build a 3D textured model of just part of the object by manually editing selected masks.

In our example we will model just the lens from images of a camera with attached lens. The lens model can then placed into a 3D scene in a 3rd party animation package (such as 3D Studio Max) for rendering and animating.

Starting Point

Load in the photographs of the complex object (in this case a camera).

Step 1

Using the automatic masking tools we can first build a set of masks of the combined object. These will be used later to help build masks for just the lens sub-part.

It is a good idea to save the project at this point. In our example we will call this project "camera_with_lens.som".

Step 2

We now concentrate on building the geometry for the lens. To do this we will select a number of key images and edit the corresponding masks so that they only include the lens and not the body. The key images should ideally show the whole of the lens part. Figure 5.7.1 shows suitable key images and the edited masks. Figure 5.7.2 shows an unsuitable image where large areas of the lens are hidden behind the body and hence the lens mask would have to be a very rough estimate.

Figure 5.7.1. Key masks for modelling the lens
Figure 5.7.2. Unsuitable views for modelling the lens
TIP:

Note that in general only a few key masks need to be edited for a sub-part. The remaining masks should still be included as they still help define the shape.

Step 3

Now save the edited masks in a new project. Use the File > Save As... menu item to save and rename the project. A good name in this case would be "lens_only.som".

Step 4

Build a mesh for the lens using the Surface Wizard which is launched by clicking on the ID_MAKE_SURFACE.jpgGenerate surface... button. Use the "Generate wireframe" option to generate an initial mesh. If required the mesh can then be optimised.

Figure 5.7.3. mesh model of the lens

If you are only interested in the object shape you can export the untextured mesh for further editing in a 3D modelling application. Edited meshes can also be re-imported for texturing from photos.

Step 5

The next step is to build the texture map for the lens. Care needs to be taken here as you will need to ensure that image data from the camera body is not incorporated into the textures.

Select a subset of the images that you wish to use to texture the subpart and reject the remaining images. Then for each included image edit the masks ensuring that any areas of the lens that are obscured by the camera body are masked out so that they are not used for texturing.

Figure 5.7.4 shows the initial mask for the top-down view and the edited mask used prior to building the textures.

Figure 5.7.4. Initial edited mask for geometry (left) and edited mask for texturing (right)
Step 6

Once the masks have been edited the texture map is generated in the usual way by clicking the ID_MAKE_TEXTURE.jpgGenerate texture maps... button.

The texture mapped 3D model of the lens can now be exported for inclusion in a 3D scene.