Page 1 Modeling a Tank: Body


Open lunar/body_curves.3dm and save it out as body.3dm on your local hard drive in a new subdirectory called tank.

What you have here is the PolyLines that form the body of the tank. The lines are based on the background sketch shown below.

Select all the PolyLines and hit Loft and use the 'Straight sections' and 'Do not simplify' options.

Overview: So basically what you see are PolyLines that where made in the top view. They were placed at the right height in the front view. In the top view, edit points were adjusted to fit the background body shape. The background used is shown below. Some other sketches by my friend Steve Pak are in the Tank/background directory on the CD-ROM.

After one line looks about right I then used Copy 'InPlace' and dragged and edited that PolyLine keeping the same amount of points in the curve. If you select all the curves and hit What you will see that they all have 24 segments. One thing you should note is that sometimes the edit points are used in the 6 curves to denote change in the shape of the body and sometimes they do not. The reason for points on the curves that do not denote change is they keep the surface in order from the top to the bottom.

Optional: If you would like to see what I mean you can delete or hide the surface and select the top curve, hit EditPtOn and hit RemoveKnot and remove the 2 knots shown circled below. Then repeat step one and you'll see that even though the points didn't change the appearance of the curve, they did maintain the surface.

Technoid Notes: about surface construction: How the points are placed in the curves effects how all loft surfaces are constructed. This is also why the rebuild option in the 'Loft dialog box' is such an important option. What 'Rebuild' does is space the points evenly on the construction curves and gives the the construction curves a equal number of points and the option of lining up where the curves start so that the surface does not have twists and bunch up in undesirable areas. In the above situation though the Rebuild option wouldn't be a desirable option because it would require to many points to maintain the rectangularity of the object, Rebuild is mostly used for organic shapes. So what is called for, to create inexpensive rectangular geometry, is to manually orient the points and use the 'Straight sections' option.

Select the surface and hit Cap, which will put a cap on the top of the tank.

Save the body.3dm file.