Applying a Transition Between the Front and Top Surfaces

To use the Rail tool

1. Arrange your screen as shown in the image below. Only the X, Y, and Z scan lines, the center line, and certain Z–curves should be visible.

   

2. Double-click the Surfaces > Swept Surfaces > Rail Surface tool to produce the option box.
3. Because there are only two curves to create the surface, use 1 Generation curve and 1 Rail curve. Pick the Z-curve first to mark it as the Generation curve.
4. Select the portion of the center line you need to create the front surface.
5. Set the Rail options as shown.

   Set this parameter...	To this value
   gen. 1 (curve #28)	Continuity set to Position, Rebld off
   rail 1 (curve #19)	Continuity set to Position, Rebld off
   Sweep Mode	PARALLEL
   Sweep Pivot	CLOSEST
   Fixed Curve	RAIL
   Rotate Xform	0.0000
   Scale Xform	1.0000
   Curve Segments	off
   Explicit Control	on
   U/VSync Degree	off
   Rail Degree (U)	2
   Gen. Degree (V)	5
   Rail Spans (U)	1
   Gen. Spans (V)	1

   

6. Repeat Steps 3 and 4 to create another surface, but reverse the selection order. The new surface differs from the original because of the selection order of the Generation curve and Rail curve.

   

7. Hide the curves and make the top surface visible.

   

A new method utilizing construction planes will be introduced to build the transition surface.

To use a construction plane

1. Choose the Construction > Plane tool. A 3-point plane will be created.
2. Using CRV snapping (press + (Windows) or + (Mac)), select a corner point of the front surface to mark the centre of the new construction plane.
3. Using CRV snapping, select the opposite corner point of the front surface to mark the X-axis point of the new construction plane.
4. Using CRV snapping, select a point between the two points already selected. The third point defines the plane. Make sure that the third selected point is snapped to the edge of the front surface.
5. Repeat Steps 3 and 4 for the other edge of the front surface.

   

If a construction plane is created using geometry (3-point plane, surface plane), the construction plane will always have an associated construction history. Deleting the geometry used to create the construction plane will also delete the construction plane, even if the construction plane is assigned to another layer. If you want to delete the geometry but maintain the construction plane, delete the construction history of the construction plane to achieve independence. If a number of construction planes are required for the modeling process, each construction plane can be named using the Windows > Information > Information Window menu item.

To intersect a construction plane with a surface

1. Select both construction planes and the top surface.
2. Double-click the Control Panel > Evaluate > Cross-section tool to produce the options box.
3. Set the options as shown in the images below.

Changing the Geometry option to NURBS will create Nurbs curves on the reference surface. The Nurbs curves have a poor CV distribution, but offer a connection history to the construction plane.

At this point in the process, your model should resemble the image below.

Before proceeding, it should be noted that the straight edge of the top surface could not be used to construct the transition surface. In the top view, the front surface displays a curved character that must flow through to the top surface. In order to transition the curved character of the front surface, apply a curve-on-surface shaped similar to the front surface.

To change the shape of an edge by trimming the basic surface

1. Duplicate the edge of the front surface to produce a curve. (Use the Curve Edit > Create > Duplicate Curve tool).
2. Move the duplicated curve in the X-direction so that the curve fully covers the top surface.
3. Switch into the top view using the Viewing Panel.
4. Project the moved curve onto the top surface.

   The model now has a curve-on-surface that defines the edge of the transition surface to be built later in the tutorial.

   NoteTo get a better view of the problem hide both intersection curves as shown in the image below.

   

   From the top view, the curve-on-surface appears to be acceptable, but in the side view, the curve-on-surface does not follow the isoparametric directions of the fillet surface.

   

5. The imbalance between the curve-on-surface and the fillet surface may produce difficulties during the process of balling the corners. To minimize the difficulties associated with balling the corners, reshape the curve-on-surface along the isoperimetric line of the fillet surface.

6. Go into the side view.
7. Select the fillet surfaces.
8. Choose the Object Edit > Patch Precision tool.
9. Press the left mouse button and slide it horizontally to the right until the isoperimetric lines resemble the image below.
10. Create a degree 1 edit point curve along the isoparametric line highlighted in the image below.

    

11. Pick the endpoint of the duplicated curve and slide the CV upwards to point beyond the top surface.

    

12. Move the curve in the X-direction to the front edge of the top surface.

    

13. Make sure that you are still in the side view and project the curve onto the side surface.
14. Return to the Object Edit > Patch Precision tool and select the fillet surface, press the left mouse button, and slide the mouse horizontally in the left direction to remove all of the isoperimetric lines.
15. You can also type a 2 into the Prompt line to achieve the same results.

    

    A new curve-on-surface is created that differs from the original straight edge of the top surface and has a better appearance in the side view.

16. Delete the original curve-on-surface.

    

Both of the curves built by intersecting the construction plane with the top surface are too long and must be cut to match the curve-on-surface.

To cut a curve using reference geometry

1. Switch to the top view.
2. Double-click the Curve Edit > Curve Section tool to open the option box.
3. Select both intersection curves as shown in the image below.
4. Press the Go button at the bottom of the screen to complete the selection process.
5. Select the curve-on-surface as a reference for cutting the selected curves.

   

Before using the Rail tool, define two blend curves between the intersection curves and the front surface.

To use blend curves to define the edges of transitional surfaces

1. Create two blend curves that resemble the image below.
2. In the Blend Curve option box, choose the BlendCrv Tools > Blend Curve Create tool and select the curves and the edges using CRV snapping (press + (Windows) or + (Mac)).

3. 

   By connecting a blend curve with a curve, the blend curve does not contain the curvature continuity required for the model. As a general rule, a blend curve connected to a curve will always contain POSITION Continuity G0. (Remember the previously completed curve-fitting section).

4. Select both blend points that connect to the curves.
5. Choose the Go button, hold down the mouse, and move until you arrive at G2.
6. Release the mouse button. The blend curves will project from the curves by a curvature value of G2.

   

To use the Rail tool to create the transition surface

1. Double–click the Surfaces > Swept Surfaces > Rail Surface tool to open the option box.
2. Set the options as follows:

   Set this parameter...	To this value
   Generation Curves	2
   Rail Curves	2
   gen. 1 (blend#12)	Set Continuity to POSITION, Rebld off
   gen. 2 (blend#11)	Set Continuity to POSITION, Rebld off
   rail 1 (rail_surf#4)	Set Continuity to CURVATURE, Rebld off
   rail 2 (square#14)	Set Continuity to CURVATURE, Rebld on
   Sweep Mode	PROPORTIONAL
   Transform Control	SCALE
   Blend Control	off
   Explicit Control	on
   U/V Sync Degree	off
   Rail Degree (U)	5
   Gen. Degree (V)	5
   Rail Spans (U)	1
   Gen. Spans (V)	1
   Create History	on
   Auto. Recalc.	on
   Boundary Labels	on
   Continuity Check	on

3. Select both blend curves, then, select the curve-on-surface and the edge of the front surface.

   

Activate the X-Cross-Sections of the new Rail surface. The updated Rail surface does not fit to the scan lines because the blend curves are flawed. To correct the problem, modify the blend curves at the same time to maintain the model’s symmetry.

To modify the blend curves

1. Select the two opposing blend points.
2. Choose the BlendCrv Tools > Blend Curve Edit tool.
3. NoteThe BlendCrv Tools > Blend Curve Edit tool will produce a single Locator that will be responsible for both selected blend points.
4. Select the blue square of the Locator, hold down the mouse button and move it until the desired results are achieved.
5. Try the same procedure with the blue sphere.
6. If the blend curves are moved correctly, the Rail surface will update to fit the scan lines.

   

If the modification of the blend curve did not achieve the desired fit to the scan lines, examine the front and top surfaces to determine if further changes are required.

When modifying the front surface, use the direct modeling method (moving the CVs of the front surface). One of the consequences of modifying the front surface using direct modeling is that the construction history of the Rail surface will be lost. As well, because the front surface runs across the plane at the Y0 position, the symmetry will need to be maintained. (Keep in mind the rules for modifying CVs that run across the Y0 plane).

When modifying the top surface, remember that the top surface has a construction history that ties it to the fillet and side surfaces. As a result, modification of the top surface will be a time-consuming endeavour because the fillet surface will also have to be updated. To speed-up the modification process, postpone the recalculations by temporarily suspending the construction history. When you have found an acceptable modification, reinstate the construction history. Another restriction against modifying the top surface is that the edge of the top surface connects to the side surface, and as such, cannot be modified because the side surfaces are the references for the top surface.

How to suspend calculations

1. Choose the H to the right of the Prompt line (above the layer bar).
2. Hold down the H button until a menu appears.

   

3. Move the cursor over Suspend Rebuilds and release.

   

   NoteA diagonal line should now cut through the H.

   

How to reactivate the calculation

1. Press the H button.
2. Hold down the mouse button and move the cursor over Suspend Rebuilds.
3. Release the mouse.

   

After finishing the front surface and the transition to the top surface, your model should resemble the image below.

Summary

• Projecting curves to create new edges may require a number of attempts to achieve the desired results.
• Projecting curves to create new edges will require extra attention because they are instrumental in producing a useful Patch Layout.
• Curve on Surfaces should be evaluated from a variety of views in order to find the best shape.

Applying a Transition Between the Rear and Top Surfaces

The rear surface will be constructed using a similar approach to that used in creating the front surface. A Rail surface will be constructed using two curves from the center line and a corresponding Z- curve.

To create the transition surface, you will use the fillet surfaces already created, but there will be no need to create construction planes or curves that intersect with the top surface.

Given the shape of the rear scan lines, the edge of the transition surface will be shaped to touch the top surface using a curve-on-surface.

To create the Rail surface

1. Create a Rail surface using 1 Generating curve (Z-curve) and 1 Rail curve (part of the center line).
2. Set the options as follows:

   Set this parameter...	To this value
   gen. 1 (curve#57)	Set Continuity to POSITION and Rebld off
   rail 1 (fit_curve#2)	Set Continuity to POSITION and Rebld off
   Sweep Mode	PARALLEL
   Sweep Pivot	CLOSEST
   Fixed Curve	RAIL
   Rotate Xform	0.0000
   Scale Xform	1.0000
   Curve Segments	off
   Explicit Control	on
   Rail Degree (U)	2
   Gen. Degree (V)	5
   Rail Spans (U)	1
   Gen. Spans (V)	1
   Create History	on
   Auto. Recalc.	on
   Boundary Labels	on
   Continuity Check	on

   

3. Arrange the scene to offer the best view of the new rear surface, the top surface, the fillet surfaces, the side surfaces, and all of the scan lines.

   

In this section of the modeling process, you will build the transition surface over the Y0 plane and maintain the construction history throughout the entire operation. You will begin the construction by creating a fillet on the other side of the model, but first, examine the options of the existing fillet. In order to produce the options box for the existing fillet, the Object Edit > Query Edit tool can be used if the construction history of the existing fillet has not been lost.

To use the Query Edit tools

1. Select the fillet surface.
2. Choose the Object Edit > Query Edit tool.
3. Step 2 produces the Surface Fillet Control box. Take note of the arrangement of the options.
4. Choose Pick > Nothing .
5. Using the same options as previously, create a fillet on the other side of the model to achieve identical fillet surfaces on both sides of the model.

   

Now you are ready to create a curve-on-surface that will be the top edge of the rear transition surface. The curve-on-surface must have the curved character of the rear surface as seen in the top view.

To shape one edge of the rear transition surface

1. Use the Viewing Panel to switch to the side view.
2. Create a degree 1 edit point curve as shown in the image below.

   

3. Remain in the side view and project the curve onto both fillets and the top surface. (Use the Surface Edit > Create CurvesOnSurface > Project tool).
4. Tumble the view to see the newly created curve-on-surface.
5. Select the curve-on-surface.

   

The resulting curve-on-surface could be split into two parts, one of which is highlighted. The entire curve-on-surface is not highlighted because there is a problem with the curve used for the projection.

To correct the curve and complete the curve-on-surface

1. Return to the side view.
2. Select the upper CV of the curve.
3. In small increments, move the CV in the X-direction toward the front of the model.

   

4. Tumble the view again and examine the updated curve-on-surface. It should now be one curve-on-surface that extends across the top surface.

   

5. Create a new layer and name it “work curves”.
6. Assign the curve you used for the projection to the new layer.
7. Make the new layer invisible.
8. Trim the top surface and both fillet surfaces.

   

To create blend curves between the rear surface and the fillets

1. Make the top surface invisible. (Use the ObjectDisplay > Invisible menu item).
2. Choose the BlendCrv Tools > Blend Curve Create tool.
3. Create two blend curves between the rear surface and the fillets.

   

To create a new Rail surface

1. Use ObjectDisplay > Visible to make the top surface visible.
2. Set the options as follows:

   Set this parameter...	To this value
   Generation Curves	2
   Rail Curves	2
   gen. 1 (blend#11)	Set Continuity to POSITION, Rebld to off
   gen. 2 (blend#12)	Set Continuity to POSITION, Rebld to off
   rail 1 (rail_surf)	Set Continuity to CURVATURE, Rebld to off
   Rail 2 (square#14)	Set Continuity to CURVATURE, Rebld to on
   Sweep Mode	PROPORTIONAL
   Transform Control	SCALE
   Blend Control	off
   Explicit Control	on
   U/V Sync Degree	off
   Rail Degree (U)	5
   Gen. Degree (V)	5
   Rail Spans (U)	2
   Gen. Spans (V)	1
   Create History	on
   Auto. Recalc.	on
   Boundary Labels	on
   Continuity Check	on

3. Create a Rail surface.
4. Select both blend curves, then, select the edge of the rear surface and the trimmed edge of the top surface.
5. Turn on the X, Y, and Z Cross-Sections for the new Rail surface.

   

Further adjustments may be required to achieve a better fit between the rear surface and the scan lines. To correct the errors, the Rail surface will have to be adjusted. However, there are a number of strategies that could be employed.

Strategies for adjusting Rail surfaces

• Modify the blend curves
• Modify the rear surface
• Modify the top surface.

The modification of the Rail surface will require the employment of all three methods. Before starting the modifications, consider the following factors that could determine the proper course of action.

Factors to consider when adjusting Rail surfaces

• The modification of blend curves is relatively easy due to the availability of a manipulator to conduct the changes.
• The modification of the rear surface will be more difficult considering the presence of previously balanced curves. To change the curves may involve unnecessary, time-consuming work. (If the Rail surface must be modified, use the direct modeling method).
• The modification of the top surface is also quite difficult because you have to take into consideration that the front transition and the fillets belong to the top surface. What appears on the surface to be an easy modification may in fact have a major impact on the model. Also, the edge of the top surface cannot be modified because the edge belongs to the side surface.

The proper course of action is to begin by modifying the blend curves.

To fit the transition surface by modifying the blend curves

1. Select corresponding blend points.
2. Choose the BlendCrv Tools > Blend Curve Edit tool.
3. A manipulator will appear. Click and hold the blue rectangle, or the blue sphere, and move each manipulator to achieve the best shape for the blend curve.

The blend curve and the transition surface will update to reflect the modifications.

To fit the transition surface by modifying the rear surface

1. Turn on the CVs of the rear surface.
   NoteYou must determine whether or not the transition surface will need to be flat or curved at the area where the rear surface has influence. If you decide that the transition surface has to be flattened, modify the rear surface in the same manner. You can achieve the surface modifications by moving CVs, but keep in mind that because the rear surface crosses the Y0 plane, you must always select the corresponding CVs. As well, when moving CVs in the in Y-direction, you will need to center the pivot before using the non-proportional scale.
2. Pick corresponding CVs or hulls and move them in the X-direction.
3. Monitor the impact that the CV modifications have on the transition surface.

   

To fit the transition surface by modifying the top surface

The top surface is related to two fillet surfaces and the front and rear transitions. When modifying the top surface, the associated surfaces will also require recalculations that could result in time delays. To avoid time delays, use the Windows > Information > History View menu item to suspend the recalculations during the modification process.

See the section entitled “The transition between the front and top surfaces” for the details concerning the suspension and reactivation of the calculations.

After finishing the modification to the rear transition surface your model should resemble the image below.