Tuesday, September 08, 2009


This is a 3-D wireframe drawing of a K-36 front pilot frame.

(left click to enlarge)

Not shown is the Bissell post, the snow plow assembly, springs, wheels and axle, and a host of other detail items.

Like most locomotives, the K-36 has few 90 degree angles to contend with. Most everything is designed with arcs and curves.

Arcs and curves are things computer 3-D drawing programs do not like.

The more points of reference that are identified on any arc or circle, the more memory it takes to store those points. It also takes more time to display it.. Refreshing or regenerating a view port can slow to a crawl when the drawings get large enough.

As an example, a straight line from point A to point B, regardless of length, takes only 2 data points, each having an X, Y and Z reference. however, a circle, regardless of size, having a point of reference every degree, has 360 data points, each having an X, Y, and Z co-ordinate. If it's a sphere, it's the square of that number, or 129,600 X, Y, and Z co-ordinates. They all have to be stored in memory.

But that's not my real problem... today's incredible computers can handle all that data easily. Look at the above wireframe. Every one of the circles and arcs have a center, a place where its radius is measured from. That center has its own X, Y, and Z co-ordinates, but this time, I have to know and label these points. They are identified using what is known as the UCS system, the Universal Co-ordinate System. The USC can be moved any place on the drawing and it can be pointed in any direction relative to the World Co-ordinate System, which is a fixed X, Y and Z used as a master reference.

When you get enough of these UCS points, it can become a nightmare just to remember them, and figuring a unique name for each one. And 3-D locomotive drawings are really just a massive collection of arcs and circles, with an occasional straight line here and there.

If you are a computer game player and play say, World of Warcraft, you will see there are no true 3-D circles or structures. They are all constructed of several straight sections, joined in such a way as to form the appearance of a "round" structure, generally using around sixteen sections. If Blizzard had used 360 sections to show the appearance of a true circle, the game would never move faster than a crawl. Don't confuse a 2-D circle drawn on the face of a 3-d structure.

I generally use 40 reference points - or isoframes - for each 90 degree segment of a circle. That's good enough to display a fairly reasonable rendition of an arc or circle. Each one of those points are shown as a straight line across the Z-axis of the arc or curve.

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