To construct the transition surface at the front

1. Open the wire file Transition Surfaces.wire.
2. Select the surfaces from the “work” layer and choose View > Look At tool.

   Use the surfaces in the “work” layer. Keep the layer highlighted in yellow so that all new geometry will be assigned to the layer.

3. Use the Viewing Panel to switch to the side view.
   NoteThe ViewCube viewing control displays by default, but you will use the View Panel in these tutorials. If you have not done so already, switch view controls, by selecting Preferences > General Preferences ❒, clicking Viewing, and then selecting View Panel. For information on the ViewCube, see Use the ViewCube tool and NavBar.
4. Create a degree 1 edit point curve that follows an isoperimetric curve of the fillet.

   In the image below, use the right-most ball as a guide to where the curve has to be positioned. Eventually, the curve will have to be moved slightly in the X-direction.

   

   NoteAn isoparametric curve is used in this procedure to maintain the natural character of the fillet.
5. Select the bottom CV of the curve and slide it down to reach the bottom level of the front surface.
6. Create a degree 1 edit point curve following the bottom edge of the front surface. The curve is parallel to the X-direction.
7. Make sure the curve is long enough to cross the curve created in Step 2.

   

8. Cut the curve as shown in the image below.

   

9. Press + (Windows) or + (Mac) to produce the Viewing Panel. Ensure that the Perspective view has not been activated. Click on the side arrow to make sure you are in the side view.
10. Project both curves onto the side surface and onto the fillet surfaces.

    

The model should now have a new curve-on-surface that resembles the image below.

The next step is to define the curves of the transition surfaces by using blend curves.

To create the transition surfaces

1. Double-click the Curve Edit > Create > Duplicate Curve tool to produce the option box.
2. Set the Duplicate Type to NO REBUILD.
3. Pick the curve-on-surface of the side surface.

   

4. Delete the curve-on-surface of the side surface.
5. Create a blend curve between the duplicated curve and the front surface.
6. Select the blend point that is connected to the curve and change the Continuity to G2.

   

7. Trim the fillet. Keep the surface similar to the dark gray area in the image below.

   

In a previous section, you fitted curves to Z-scan lines. The curves created in that section served as guides for establishing the correct Patch Layout. The curves created in this section are designed to serve as the framework of the surfaces. To ensure that the curves created in this section are correct, check the curvature combs of the curves.

To create and modify a curvature comb

1. Select the two curves.
2. Calculate a curvature comb over both curves using the Locators > Curve Curvature tool.
3. Use the to adjust the density of the curvature comb.
   TipBy moving the right mouse button, you can adjust the size of the curvature comb.

   

   NoteIf the resulting curvature comb resembles the image above, the comb may have an imbalance caused by the abrupt change between the curvature of the blend curve and the duplicated curve. To correct the curvature comb, manipulate the blend point.

To correct the curvature comb

1. Select the blend point and move it by curve snapping (press + (Windows) or + (Mac)) along the duplicated curve.
2. Watch the curvature comb.

   

   NoteModifying the curvature comb may change the impression you achieved by fitting the Z-scans (the size of the transition surface). However, the side surface has more value when judged as a Z-curve, and as a result, the new modifications should be kept.

To continue with the modeling process, prepare the model for the next required transitional curve.

The fillet surface was created using the CURVES ON SURFACE setting found in the Trim Type option of the Surfaces > Surface Fillet tool. To avoid confusion when creating the next transitional blend curve, hide the curve-on-surface using the Object Edit > Query Edit tool. The Object Edit > Query Edit tool reproduces the option box, or control box, of the tool you used to create the selected surface. In this case, it is the Surface Fillet Control box. In the control box, change the Trim Type to OFF.

Because you slid the blend point along the curve associated with the side surface, the trim curve of the fillet surface will also have to be moved.

To snap a curve to a pre-defined point

1. Switch to the side view.
2. Make visible the curve previously used to trim the fillet surface.
3. Set the pivot point at the lower end of the curve.
4. Move the curve to the new position of the blend point, marked in the image below with a large sphere.
5. To find the exact position use the Magnetic Snap (press (Windows) or (Mac) and click close to the blend point).

   

This will change the curve-on-surface on the side surface as well as the curve-on-surface of the fillet surface. The next step will be to create the other transitional curve that will become the foundation for the transitional surface between the side surface and the front surface.

But before creating the transitional curve, hide the curve-on-surface on the side surface by using the Object Edit > Query Edit tool.

To use Query Edit to hide the curve-on-surface

1. Choose the Object Edit > Query Edit tool.
2. Pick the edge of the fillet surface. The option box will appear.
3. Set the Trim Type to OFF.
4. If the recalculate option is turned off, press Recalc at the bottom of the options box.

   

To add a square surface

1. Create a blend curve between the fillet surface and the front surface. Because you hid the curve-on-surface, the fillet surface can be selected without clutter.

   

2. Set the options of the square surface as shown in the options displayed in the image below.
3. Turn on the CVs.

   

   TipThe resulting transitional surface might not fit to the scan lines. Adjust the transitional surface by modifying the shape of the blend curve.

To begin the modification of the transitional surface, note that the bottom blend curve is connected to a point inside of the curve on the side surface. For direct modeling purposes, the current blend curve arrangement is not favorable for modification. To enable alignment using the Object Edit > Align > Align 2008 tool, cut the reference curve at the point where the blend curve intersects the reference curve.

To cut the curve on the side surface and align the transitional curves to the references

1. Use the Viewing Panel to switch to the side view.
2. Make the newly created transition surface invisible.
3. Open the option box of the Curve Edit > Curve Section tool.
4. Set the options as follows.

   Set this parameter...	To this value
   Sectioning Mode	Trim
   Sectioning Criterion	Geometry

   

5. Press the Go button at the bottom of the option box.
6. Select the curve at the point highlighted in the image above.
7. Press the Go button at the bottom of the screen.
8. Select the other curve involved in the process.

   The next step is to align all of the curves to their references by curvature. As a result, all of the former blend curves will gain an additional kind of history that allows CVs to be modeled directly.

9. Double-click the Object Edit > Align > Align 2008 tool to produce the option box.
10. Select each end of the two blend curves and align them to the reference.

    

11. After the curves are aligned, choose ObjectDisplay > Visible to view the transition surface.

To avoid confusion when selecting curve CVs

1. Open the ObjectDisplay > Control option box.
2. Select the transition surface.
3. Set the options as follows.

   Set this parameter...	To this value
   Scope	ACTIVE
   Key Points	off
   Hulls	on
   Edit Points	off
   Blend Points	off
   Poly Normals	off
   Surface Iso	off

4. Press the Go button.

Although the CVs of the selected surface are hidden, the hulls that act as guides for the CV distribution are still visible. The CVs of the curves are also visible and can be selected without having to navigate a selection window.

To change the fit of the transitional surface by modifying CVs

1. Choose Pick > Nothing .
2. Select the transition surface.
3. Turn on the X, Y, and Z Cross–Sections.
4. Modify the CVs of the curves using the Control Panel > Evaluate > Move CV tool set to SLIDE.
5. Watch the sections on the surface.

   

The resulting surface may be flawed if a smooth fit could not be obtained between the transition surface and the scan lines. One factor that could determine the success or failure of the transition is the smoothness of the distribution of the CVs across the transition surface.

If an acceptable result cannot be achieved, increase the degree of your curves to 6.

To increase the degree value

1. Select the first curve.
2. In the Control Panel, increase the degree value from 5 to 6.
3. Press the Accept button at the bottom of the screen.
4. Choose Pick > Nothing .
5. Select the other curve.
6. Increase the Degree value to 6.

To continue, adjust the degree of the transition surface. (Remember, by using the Object Edit > Query Edit tool, you can reproduce the option box of a surface that has a construction history).

To adjust the transition surface

1. Choose the Object Edit > Query Edit tool.
2. Pick one edge of the transition surface. The Square Control box appears. If it does not, try repicking the edge.
3. Change the value of the degree from 5 to 6.
4. Choose Pick > Nothing .

   

At this point, for each curve you should have one independent (free) CV that is not related to a curvature alignment. The new curves offer more freedom in fitting the transition surface to the scan lines. Within the confines of this tutorial, do not exceed a degree 6 curve. One free CV should be sufficient to maintain a good fit between the transitional surface and the scan lines.

If all CV modifications have been implemented and the results are not satisfactory, change the front surface in the same manner used to create the transitions between the front/rear surface and the top surface.

Successful modifications of the model should produce results that resemble the image below.

For the next step, try to construct the transition surface at the rear of the model by using the same methods already employed. Reference the images below for tips.