2.4. Building the wireframe model

The wireframe model is the second stage in generating a 3DSOM Pro model. The wireframe model represents the shape of the model as a triangle mesh. 3DSOM Pro uses the mask associated with each of the images to deduce the shape of the object from its silhouettes.

The basic operations for the wireframe model are described here...

2.4.1. Generating the wireframe

Starting Point

You should have created masks for a sufficient number of images before you can do this operation. The minimum requirement is three masked images but you will usually need around 10 to 30 to capture the shape of a typical object.

To try this out, load the doll.som project from the Examples directory with your installation which already has images masked — it already has a mesh created but you can generate a new one.

Step 1

The wireframe model of the object is generated with the help of the Surface Wizard which is launched by clicking on the ID_MAKE_SURFACE.jpgGenerate surface... button or the Processing > Generate Surface... menu item.

When the Surface Wizard is opened choose the first option, "Generate wireframe", to create the initial surface and then click the Next > button to proceed to the next page of the wizard. The other options are described in the Optimising the surface geometry and Improving the geometry with subdivision surfaces tutorials.

Step 2

You can alter various parameters associated with this operation before generating the wireframe. The default values will be sufficient in most cases (the options are described in detail in The 3DSOM Pro Settings Window section).

Step 3

Click the Next > button to start generating the wireframe.

You won't see any results until the process has completed, but you can cancel part-way through if it is taking a long time. Try hitting < Back button then increasing the "Silhouette decimation threshold" or reducing the number of images to reduce the time.

TIP:

If you are experimenting with changing parameters, you can return to the last wireframe you generated by closing the Surface Wizard then using the ID_EDIT_UNDO.jpgUndo model or mask change button

2.4.2. Adjusting the decimation

The model is stored as a triangle mesh and a technique known as decimation is used to allow the number of triangles in the mesh to be varied interactively.

It is possible to adjust the decimation of the wireframe model using the slider in the View Model toolbar. Moving the slider to the left decreases the model's polygon count (reducing the definition of a model), whereas moving the slider to the right increases the model's polygon count (improving the definition of a model).

Note: If a Decimate button is displayed in the place of the slider, then click this and wait for the decimation information to be pre-calculated. This can occur after cancelling certain operations.

3DSOM Pro keeps all the triangles internally, so you can always change the number currently used for display later (even after a texture map has been created), however the following operations will use just the triangles currently displayed in the mesh:

TIP:

Use as many triangles as you require to model the object and no more. The best way to choose an appropriate number is to view the model either using View textured model (F7) or View flat shaded model (F6) mode and then reduce the number of triangles until you see unacceptable artefacts.

Why might you want to change the number of triangles? Models with large numbers of triangles are slower to download over the web and require more processing power to display. The Web Optimizer tool tutorial describes how to balance these requirements for exporting to the 3DSOM Viewer format.

2.4.3. Clipping away the stand

Sometimes there will be unwanted geometry at the base of the object as in Figure 2.4.1. This can be due to no images being taken from a low down angle (to ensure the calibration mat was visible). Also, the stand may have been treated as part of the object and not the backdrop in the masking process.

Figure 2.4.2 shows the model after clipping has been used to remove the unwanted geometry.

Step 1

Choose a side view of the object such as the one shown in Figure 2.4.1 where you can clearly see the geometry you want to remove.

Step 2

Select the ID_MODEL_MOVECLIP.jpgMove clip plane button tool and you will see a clip plane displayed below the model.

Drag the mouse with the left button pressed upwards, moving the clip plane up until it is placed at the desired location. All the geometry below the plane will be removed.

TIP:

At this point, a quick way to rotate the model to see the clip plane from a diffent angle is to hold down Ctrl to temporarily switch to the rotate model tool.

Step 3

Click the ID_MODEL_CLIP.jpgClip model button and wait while 3DSOM Pro remeshes the object without the unwanted geometry.

You can use ID_EDIT_UNDO.jpgUndo model or mask change button to return to the previous geometry if you have removed too much.

If you decide not to do the clipping operation, you can hide the clip plane by dragging it down below where the mat would be.

2.4.4. Improving the Surface Geometry

Figure 2.4.3. Improving the surface geometry example

The surface generation tools described in this section are just the starting point. 3DSOM Pro version 3 now includes a host of additional tools for improving the geometry to create more accurate models. Here are some of the ways you can improve the model...

Additional techniques can be found in the following tutorials: