Cross Section Modelling - Part 2

In part 2 of this tutorial we will give our cross section depth.

bulletIn part 2 of this tutorial we will use the original source image we used in part 1.

 

 
bullet3D Canvas supports the use of side, top and front view images as modelling aids.

The 3D Canvas grid can be replaced by these custom images.

For more information on using images as plans for modelling see Using Backdrop Plans.

From the traced image I have created a side view plan.
 

 
bulletA front view is also required. The front view image must be the same proportions as the side image, and be placed at the same height as the side view image.

In this example, the height of the model in both plans is 180 pixels and there are 60 pixels of white space at the bottom of each plan.
 

 
bulletOpen the cross section model created in part 1.
 

 
bulletIt is best to have four views when cross section modelling: a perspective, a front a top, and a side view. You can select your view by choosing View Selection from the View menu.

 
bulletVertical grids can also be handy for modelling using a cross section. These can be enabled through the 3D Canvas Options which are available on the Tools menu.

Since we are not using a bottom view it is a good idea to change the size of the default grid to be at least as long as your side view is in real world units. In this example, the model will be 30 units long. I have changed the size of the grid to 35 units.

 

 
bulletClick on the Primary Toolbar to indicate that you will be using a side view backdrop plan.

Click to select your side view image.
 
bulletClick on your plan and draw a line from one point to another on the plan. This should be a known length. Enter this length.

Click OK.

Repeat this procedure for the front image.
 
bulletSelect (Backdrop) from the Grid Options on the Primary Toolbar. This will display your backdrop plans.
 
 
bulletPosition the cross section so that it is centered on the front view of the object. Scale the cross-section by Ctrl-dragging so that the cross section matches the front view exactly.

If you look at your side view it should be centered vertically as well. If it is not then the background images likely need to be corrected. See the earlier steps on background image preparation for more information.
bulletPosition your cross section so that its right-most edge is at the center of the side view image. We will be modelling towards the left (front) side of the model.
bulletMost work will be done from the side view with the group-point/face selection tool which is available on the edit toolbar by clicking . Selecting with this tool selects not only the point closest to you, but the point on the other side of the object. This ensures equal movement for both sides. In this mode you will have to use the edit control to move the points. Make sure you use the constrain buttons , and (located on the main tool bar) as required to ensure that you do not unintentionally move points on an axis you are not intending. Remember that when modeling in the standard modelling mode (rather than world, screen, object, or face) that constrain is in world coordinates.

Select the entire left-most cross section by dragging a selection rectangle around it. Move it, using the edit control, to the left until you reach a place where the cross section changes. Don't worry about cut-out details like the wheel well or the pantograph well. We will be creating these details later using Boolean operations. Note that if you do not have 3D Canvas Pro you will need to model these parts now as the freeware and Plus versions of 3D Canvas do not include Boolean operations.
 
bulletAt this location, the model has a slight curve. In order to properly follow this curve we will need more cross sections.

Select the leftmost face (the cross section face) and use the Extrude operation to extrude it. Once you have extruded, position the cross section as shown. Extrude a second time and position it as shown.

Note: if your cross section is concave, rather than convex, you may find that you have many triangular faces instead of a single face. If this is the case, you can select all of the triangles by alt-selecting one of the triangles.
bulletSelect the top most points and shift them down to follow the curve.
bulletWe will continue with this process, trying to achieve a curve that resembles the front of the engine. Keep in mind that in 3D there is no need to provide a consider amount of detail since 3D shading effects are used to increase the appearance of smoothness.
bulletContinue extruding and shifting points as necessary to follow the curve of the model.
bulletIt is necessary when modelling using a cross section to keep a close eye on the front view.

It helps considerably to have a few perspective photographs of the real object you are modelling. The front and side views rarely give the whole picture. In this case simply shifting points down was not enough. A look at the real object indicates that we also have to move some of the points horizontally as well as vertically.
bulletA corrected front view.
bulletHere we have a perspective view rendered in in Solid Outline mode. Solid Outline mode can be handy in the early stages of modeling and is available on the main toolbar from a drop-down list.
bulletFurther extrusions following the curve.
bulletAnd shifting of points to follow the curve.
bulletBe sure to watch front views, and perspective views while modelling to ensure that the general shape looks correct.
bulletAgain, a look at a photograph of the real object indicates that the outermost points of this new cross section must be shifted toward the outside edge.
bulletAgain we look at the perspective view to confirm that the shape is correct.
bulletThe nose requires a considerable number of extrusions to ensure adequate curvature.
bulletIt is best to have many cross sections where there is a considerable amount of curvature.

Shift the points along the top down to meet the curvature.
bulletThe bottom part of the nose requires a bit more work since there is an indentation.
bulletTry to keep the cross sections smoothly distributed as you follow the curves and indentation at the bottom.

 
bulletThe glaring weakness in this model is that we do not have enough detail at the bottom to follow the bottom part of the nose.

We will add that detail in part 3.