Wednesday, July 23, 2008

Engineering Essentials - Segment Four (Orthographic Drawings)

In discussing the orthographic drawing for vehicle prototypes, I noticed that the original sketches of the side of some vehicles don't seem to match the proportions of the orthographic tape drawing. When I raised the question as to why there was a difference, Ben explained that often times when a designer sketches the side of the vehicle it isn't necessarily from a straight on perspective, but may be either from the perspective of viewing the vehicle from a slightly upward or downward angle, depending on the vehicle. For example, for a larger vehicle like a truck or SUV, you don't see over the roof line so it would be sketched from the perspective of looking up at it. On the other hand, for a lower vehicle like a 2 door coupe, in the designer's original sketches, you may see more of the roof line so the sketch would be from looking down at the car. As the perspectives change, the reflections off the body panels also change. Shading and reflections give a 2D sketch the depth to represent what the car would look like in 3D.

images.traderpub.net


http://car-blueprints.narod.ru


The difference in going from a sketch to the orthographic tape drawing is that you aren't using perspective to show a "round" vehicle, or colors or value to represent the reflections and surfaces. To represent the complex curvature in 2D on the tape drawing, essentially what you're doing is taking the centerline features and bringing them to the front of the drawing to represent a straight on view, from every point, of what the vehicle's curves look like. This is where the difference in the profile between the initial sketch and the orthographic come from. This seemed counter intuitive to me at first, but after having it explained, it makes sense that although often times you may think you're looking at a vehicle from straight on, your eye doesn't necessarily perceive the vehicle as such, due to the perspective of seeing an object from a single vantage point.

Therefore, the tape drawing is used in conjunction with the original sketches as a tool to grab data to model the vehicle's curvature in 3D. If you were to skip the orthographic tape drawing step in the design process and model in 3D CAD using only a designer's hand sketch, the vehicle may come out looking somewhat flat due to the notion I mentioned of sketching from what I'll call from a perspective view. The orthographic tape drawing is a data point to represent the exact curvature of the body in four views (front, back, side, top) critical in avoiding a flat design since it represents these views with all of the packaging constraints in addition to the curvature at the center of the body.

Not being an artist, and not having formal transportation design training, this was very interesting to learn and I hope to continue to further my knowledge of "the other side". Although I may never be the one to create the sketches or tape drawings AND engineer the vehicle (although the thought does interest me), having an understanding of this process is critical in our ability to destroy the convention of design and engineering collaboration (or lack thereof), and as a result our ability to deliver a differentiated overall customer experience, not just a differentiated product.

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