### Constructing a Dependent/Independent Surface

All constructed surfaces start out as dependent surfaces and must be created from a single input -- a patch scan. The patch scan must contain at least two rows with four points per row. Thinning tolerances are used to control the tightness of the surface fit.

- Small tolerances: If the thinning tolerances are small, the algorithm will attempt to fit the surface through all of the points in the scan.

- Large tolerances: If the thinning tolerances are large, the surface will be more of an approximation to the scan. The best way to see this is to construct a surface and then change the thinning tolerances and see how the shape of the surface changes.

Note: The smaller the thinning tolerance the longer it will take to create the surface. Be aware that the small tolerances (.01 - .05) may take a considerable amount of time (one hour) to create the surface if the input scan is large or not well behaved. Valid thinning tolerances range from 0.01 to 5.0 with the default being 0.5.

The appearance of the surface can be controlled by the surface grid density values. The surface will be displayed as an N x M mesh of polylines with the default being a 5x5 mesh and the lowest value being a 2x2 mesh. To make a dependent surface independent so that it is no longer associated with the input scan, change the DEPENDENT field in the Edit window.

Note: The shape of the surface cannot be changed.

To construct a Dependent / Independent Surface:

1. Access the Construct Surface dialog box (Insert | Feature | Constructed | Surface).

2. Set the value for the Thinning Tol U: box

3. Set the value for the Thinning Tol V: box. This applies a tolerance value to the V axis.

4. Set the values for the surface grid density.

5. Checkmark the desired constructions options. These include:

- Optimize Surface

- Apply Tension Factor

- Create Corners

- Smooth Bad Data

6. Select a patch scan feature set containing at least 2 rows with 4 points per row.

7. Click the Create button.

More:

Thinning Tolerance

Thinning Tol U

Thinning Tol V

Surface Grid Density

Optimize Surface

Apply Tension Factor

Create Corners

Smooth Bad Data