
	Interpolating

When you cut slices though hundreds of faces you will get lines made up of hundreds of points. This isn't always the best sort of line to import into modeling software. The lines are very accurate, but cumbersome to work with. More usable, albeit less precise, lines can be created by interpolating the slice lines with a fewer number of points.

Pick the lines you want to interpolate. Then type the number of points you want into the Points field (see Figure 294). The more points you select, the more closely the interpolated lines will follow the mesh geometry. But many times you will get more aesthetic smoother lines with fewer points.

Figure 294. Interpolating

Next select either Line, Spline, Adaptive Spline or Even Spline. Given the same number of points, splines will usually follow the shape of a curved mesh better than lines. In Figure 295 you can see the original slices in red, a 10 point interpolated line in blue towards the top, and a 10 point interpolated spline in purple towards the bottom; the spline is a much better fit.

Figure 295. Line vs. Spline

The interpolated polylines and splines, once created, are placed in the Out layer. You can now either hide the picked slice lines by pushing them onto the Temp layer, or by deleting them.

Adaptive Splines

When you select Spline each picked slice is interpolated with a uniform spline with equally spaced control points. These splines are good for skinning; each adjacent spline has an equal number of control points that line up.

Figure 296. Adaptive Splines

However, uniform splines are not good for interpolating slices with variable curvature. On the left side of Figure 296 you can see a slice in red, and the interpolated uniform spline in purple. To properly fit the tightly curved areas of the slice you would need to use a uniform spline with a larger number of control points. But then, on flatter areas of the slice, you would be using lots of control points that you don't need. What you really want is more control points in the tightly curved areas, and fewer in the flatter areas.

By selecting Adaptive Spline you will be interpolating each picked slice with a non-uniform spline. These splines will use more control points around areas of tight curvature, and less around flat areas. On the right side of Figure 296 you can see a non-uniform spline fitting the same slice more closely, even though it has the same number of control points as the uniform spline.

Be warned though; because adaptive splines fit themselves to the local shape of the mesh more closely, adjacent splines will have different control point positioning. For the technical amongst you, adjacent splines will also have different knot vectors. These sorts of splines are no good for skinning, but are well suited as profiles for sweeping.

Even Splines

The interpolation schemes described above create an equal number of control points on all selected polylines. If you have a mixture of short and long lines, the long lines will have control points spaced widely apart, while control points on the short lines will be bunched together (see left side of Figure 297).

Figure 297. Equal and Even Interpolation

To get a more even spacing between points, the Even Spline tool can be used (see Figure 298). Enter the approximate spacing between control points into the Spacing field, click on the Even Spline button, and the picked polylines will be interpolated with splines, each with control points spaced the defined distance apart (see right side of Figure 297).

Figure 298. Even Spline Tool