EFFECT

Web

The Effect->Web command in the Model module allows you to convert a detailed, intricate model to a surface that represents only the external appearance of the original, ignoring any internal structure. The output surface can be a polygon mesh, or a cubic or quadratic NURBS surface.

The Web effect is designed to retain overall form, while greatly reducing the number of control points required to represent the surface. Because of this, it does not produce good results when a model has small but critical details.

The Web effect works by drawing a web-like "sleeve" around the model, using a non-NURBS curve as a guide. This sleeve is then collapsed until it fits the model; the process is similar to shrink-wrapping an article in plastic.

Depending on the settings, there may be an additional pass. This second pass uses raytracing to project the results of the first pass onto the model. The projection may be parallel or cylindrical.

The Web effect is a useful first step before using the Effect->CreateNURBSNet command to convert a model to QTMs (quadratic texture maps), particularly if you also want to simplify the model and lose detail.

It is also useful for converting heavy objects, such as those from a three-dimensional geometric scanner, into reduced models with quadrilateral polygons.

Note:

Because the Web effect does not preserve deformation or shape animation, it should be applied before you define any such animation for the model.

Procedure

Applying the Web effect involves two procedures:

Apply the effect the first time to create a web icon representing the effect. The web icon is a polygon mesh object that stores information about the effect and its settings. You can select the icon in the same way you would select any other model, but it does not appear in a Shade view or a rendered image.
Modify the effect by editing its parameters until you achieve the desired results.

: The web icon is not included when you save your scene. You should make sure that you are satisfied with the effect before you save your scene and exit SOFTIMAGE 3D.

Applying the Effect the First Time

Create a polygon mesh model.
Select the entire hierarchy, and freeze the transformations with the Effect->Freeze->Transformations command in the Model module.
If you want the Web effect to resample textures, bind the textures to the uv coordinates of the object using the Txt_Oper->Info UV Coord. (2D Global) command in the Matter module.
Draw a non-NURBS curve to use as a guide for the Web effect's "sleeve," inside or near the model. The curve does not need to follow the model exactly. However, to achieve the best results you should keep the following points in mind:

Place the control points of the curve near where features in the model change.

If the model has any u-shaped bends, the curve should be inside the model and follow the bend. In step 6 of this procedure, make sure to set Radius to a value that avoids sampling both branches of the bend at once. Otherwise, the resulting surface wraps around only the outer contour of the bend.

If you want to cap the top or bottom of the resulting surface automatically, the curve should start and stop near the ends of the model. Otherwise, the caps may project away from the model to the end points of the curve.

Curves of high curvature can yield unexpected results if they are near the centre of wide models. This is because different segments of the sleeve intersect within the model. To avoid this problem, place the curve close to the inside of the model's curve.

You can use any type of non-NURBS curve, but B-Splines generally produce the best results.

Bezier curves require at least four control points.

Choose Effect->Web. The Web dialogue box is displayed:
Accept the default options or enter new ones, then click Ok.
Pick the guiding curve.
Pick the model to apply the effect. A web icon is created and remains selected.

Modifying the Effect

Make sure that the Single menu cell is chosen, and select the web icon representing the effect.
Choose Effect->Edit Parameters. The effect's dialogue box is displayed.
Set the parameters as desired. For more information, see the next section, Parameters.
Do one of the following:

If you want to return to the original model, select Original.

If you want to undo the last Reapply action, select Undo.

If you want to apply the current parameters to the original model, select Reapply.

Do one of the following:

To apply the current settings to the model, click Apply. The dialogue box stays open and the display behind the dialogue box is updated.

To save the current settings and close the dialogue box without applying the effect, click OK.

To close the dialogue box without applying the effect or saving the current settings, click Cancel.

Parameters

Settings

The options in the Settings area control the size and complexity of the sleeve that is shrunk around the model. The sleeve is like a twisted cylinder that follows the guiding curve. It is divided into disc-like slices. These slices are used to sample the model; when the Web effect runs, it considers only the set of points of the model that fall within a slice.

Slices

The Slices option specifies the number of disc-like segments in the sleeve between each pair of control points on the guiding curve.

Sides / Slice

The Sides / Slice option specifies the number of sides in each slice. It should be set to a value that corresponds to the shape of the model.

Slice Volume

The Slice Volume options control the size of the slice that is used to sample the model. The Width option controls the thickness of the disc; it is expressed as a proportion of the distance between slices.

The Radius option controls the maximum distance from the guiding curve at which the Web effect samples points. If this value is zero, the Web effect samples points at any distance. If the model contains
u-shaped bends, you should set the Radius to a value that avoids sampling both branches of the bend in the same slice.

Capping

The Capping options control whether the resulting surface is closed at its ends. Top closes the top and Bot closes the bottom.

Note:
If you select these options, the guiding curve should start and stop near the ends of the model. Otherwise, the caps may project away from the model to the end points of the curve.

Webbing Method

The Webbing Method options specify the method used to create the final surface.

Cylindrical Convex Wrap

This method simply shrinks the sleeve around the model until it fits. It is the quickest method and produces acceptable results in many cases. However, if the model contains concavities which must be kept, use one of the other methods.

Cylindrical Projection

This method is a two-step process. The first step creates a surface using the Cylindrical Convex Wrap method. The second step uses a raytracer to map the contour of the model by casting a ray from the first surface to the centre of the data in each ring.

This method is useful for models that are topologically similar to a cylinder (that is, just about anything with both thickness and height), and which also contain concavities that are not handled properly by the Cylindrical Convex Wrap method.

Parallel Projection

This method uses a raytracer to map the contour of the model using a parallel projection. The rays are cast from a uv grid with the same dimensions as the "spider's web" of the effect's icon. The direction and length of the icon's "arrow" determine the direction and length of the rays; points in the model that are outside this range are ignored. You can control the effect by modifying the size and orientation of the icon.

This method is useful for models that are topologically similar to a plane (that is, very flat), and which also contain concavities that are not handled properly by the Cylindrical Convex Wrap method.

Type of Model Generated

NURBS

This option converts the model to a NURBS surface.

Cubic creates a cubic NURBS surface: this option gives greater flexibility and is better for general modelling.

Quad creates a quadratic NURBS surface and may be required when creating models for certain graphics hardware. Select this option if you will be creating QTMs from the resulting NURBS surface with the Effect->CreateNURBSNet command.

The Points options specify the number of control points in the U and V directions of the final NURBS surface. If these values are zero, the final surface will have the same number of points as the sleeve. High values may cause tensor artifacts, such as bulges. If you don't get the result you want, try decreasing these values.

Note:
When the Web effect creates a NURBS surface, the U and V directions are interchanged and the U direction is inverted, compared to other NURBS surfaces in SOFTIMAGE 3D.

Polygon Mesh

This option converts the model to a polygon mesh object with quadrilateral faces. It typically results in a more detailed result than the NURBS option. You can also select this option if you will be creating QTMs from the resulting surface with the Effect->CreateNURBSNet command.

Processing Options

Process All, Tagged Only, and Untagged Only

These options control which points on the model are considered by the effect.

Process All considers the entire model.

Tagged Only considers only those points that have been tagged.

UnTagged Only considers only those points that have not been tagged.

You must tag points before displaying the effect's dialogue box. To tag or retag points while using an effect, you must close the dialogue box using Cancel or Ok, change the tagging on the model, then display the dialogue box again.

Follow Hierarchy

This option applies the settings to the entire branch of the hierarchy below the selected model. If this option is selected, the resulting surface replaces the root node only; the child nodes remain in the scene, even though their shapes are reflected in the resulting surface. If this option is not selected, only the root node of the selected branch is considered by the effect.

Process Nodes Individually

This option creates separate surfaces for each node in the hierarchy. If this option is not selected, the root of the hierarchy is converted into a surface that represents the entire model.

Resample Textures

This option tries to preserve the overall look of any textures applied to the original model. Textures are resampled and the new texture is applied to the final surface.

The resampling process also includes any material information in the new textures. This is necessary because the geometric primitives that make up the original and resulting models have different boundaries. For example, a NURBS surface in the resulting model may correspond to many polygons in the original.

Specify the degree of resampling in texture elements (texels) per SOFTIMAGE unit. The default is 20. Use higher values to keep more detail, and lower values to eliminate more detail.

When generating a NURBS surface as output, a single texture is created. When generating a polygon mesh, a separate texture is created for each face.

Textures are created in the current directory. However, you are prompted to move them to the PICTURES directory when you save the scene. If you are not running SOFTIMAGE 3D from your home directory, make sure that you have write permission for the current directory; otherwise, textures cannot be generated.

Original, Undo, and Reapply

These options control the operation performed when you click Apply (or Ok if you are running the effect for the first time):

Original returns to the version of the model as it was before any effect was applied.

Note:
When you select Original and click Apply, the model may appear faceted. To see a smoother version, select the model, choose Info->Selection, select the Automatic Discontinuity option, and click Ok.

Undo Last undoes the last Reapply operation. It does not undo an Original or Undo Last operation.

Reapply applies the current settings to the original version of the model.

Tip:
If you have difficulty applying an effect, or have unexpected results, it is often because you selected the wrong option from these three. Check that the correct option is selected before clicking Apply.

Apply, Ok, and Cancel

The Apply button applies the current settings to the model and leaves the dialogue box open. This allows you to experiment with different settings until you achieve the desired result.

The Cancel button closes the dialogue box without applying the current settings. If you entered any new values, these changes are lost.

The Ok button behaves differently, depending on whether you are running the effect for the first time or editing parameters. The first time you run an effect, this button applies the current settings and closes the dialogue box. When editing parameters, this button closes the dialogue box without applying the settings. If you open the dialogue box again, the last settings entered are still displayed.

Last updated 02-apr-1998