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The Vector dimension

Posted on 5 Apr 2004 at 10:46

Tom Arah goes in search of ways to bridge the great 2D/3D divide

Back in issue 113, I examined the importance of 3D graphics for realistic illustration, and how the major 2D drawing applications have begun to embrace this fact. They still have a long way to go however, so how else can you bring your vector drawings to realistic life? The ideal would be to simply extend your existing 2D skills into the third dimension, and SketchUp 3 from @Last Software ($475) promises just that. In many ways, SketchUp operates like a traditional 2D vector application with a Drawing toolbar providing the basic rectangles, ellipses, curves, polygons and lines. As you draw, coloured dots and lines appear that help align your work to the existing geometry by snapping to edges, midpoints, tangents and so on.

Once you've drawn your objects, you can select and group them and reposition, scale and rotate them using the tools on the Edit toolbar, which also provides a Paint tool for applying flat colours or tiling with bitmapped textures.

SketchUp moves into new territory with its Views toolbar - so far, you've been working in Top view, looking down on your artwork from above, but you can also switch to Front, Back, Left and Right views. There isn't much to see yet, as of course your object is completely flat, but switch to ISO view and you'll get an isometric projection that shows the artwork perspectivised as if it were laid out flat on the ground. Using the tools from the Camera toolbar, in particular the Orbit tool, you can alter this perspective exactly as you want it. This is a big step up from managing perspective in a traditional drawing program, but so far all your objects are still resolutely two-dimensional.

This is where SketchUp works its magic: the Push-Pull tool in ISO view lets you to select your shapes and drag them upwards to extrude them, turning a rectangle into a cube, for example. You can then use the other Edit tools with these new 3D objects - scaling the top surface of the cube down to a point, for example, creates a pyramid, while moving the surface creates an angled effect. Once you get to grips with just what's possible - offsetting surfaces, rotating planes and edges in 3D space and so on - you can create advanced 3D shapes in seconds.

Even more impressive is SketchUp's ability to interactively draw 3D shapes from scratch, thanks to its underlying 'inference' engine (which generates those constantly appearing coloured snap lines when you draw in 2D). SketchUp's stroke of genius is to extend this idea by watching for connections to the existing 3D geometry and the main drawing axes: this takes a bit of getting used to but eventually becomes second nature. Adding a roof to your extruded rectangle, and then a dormer window, takes just a few lines and a few seconds.

Being able to literally 'sketch up' a 3D model this way is creatively exciting, but so far I've only been talking straight lines and flat surfaces, and of course the real world is much more complex than that. How do you add a curved object like a cylinder or cone? It doesn't seem like a big problem - simply draw a circle, then use the Push-Pull tool to pull it into a column and the Scale tool to point it into a cone. Behind the scenes, though, SketchUp is actually using a workaround by breaking that circle into short line segments and stretching them into co-planar surfaces: its built-in (and customisable) smoothing algorithms make the cylinder and cone look curved onscreen, but if you turn on the display of hidden geometry, you'll see how the effect is produced from flat planes. Generally this workaround works well - any shape can be broken down into a series of smaller triangles, which are by definition co-planar - but drawing a highly curved shape like a sphere from scratch this way would be almost impossible. Instead, SketchUp provides spheres as comparatively crude, ready-drawn components, but you can forget about creating realistic organic 3D objects like human faces or figures.