Tracing - 70% of Tech-Illustrations are born this way!

Ask any tech-illustrator about the kind of work which takes up majority of his time, pat will come the reply 'Tracing'. Tracing is a fundamental method of creating technical illustration line work. It is something which I personally dislike doing it, as it is a monotonous task and involves pretty much less use of creative side of my brain. Well, that's me!

Actually photo tracing or tracing as many of us love to call this activity, is useful when dimensions, engineering drawings, or CAD data do not exist, but when photographic data does. Tracing is the first step in creating accurate line work for technical graphics. So even though it is a boring thing, I will try explaining why it is so important and yes Tech-companies do have big projects which involve only tracing and creation of line-work. It is a huge profit raking activity with minimum error margin for these companies.

Why Tracing?

It is common, when assigned a technical illustration task, to be presented with photographs as the only source of information about the job. Possibly, the assembly or product you are illustrating is a custom prototype, and no drawings exist. Or such significant changes have been made that drawings, if they do exist, are worthless. Usually I have seen this happening with most of aircraft programs as they tend to be pretty old like 1990's. I love to call them 'Pre-Illustrator' era graphics. If you are used to working from CAD data or engineering prints, and neither is available while photographs are, you must be able to use the photographs. The photo tracing technique is usually faster and more accurate than starting a construction from scratch. Results are directly proportional to the expertise of illustrator doing the tracing.

Photographs Really?

Photographs have two advantages:

  1. A photograph reflects the actual condition of the subject - If the technician is under belly of an hot engine carrying out task, he is sure as hell gonna ignore installation diagram, in this case the photograph on the package illustrates how the product looks when it's shipped.
  2. Sizes and geometric relationships are correct - You don't have to worry whether you have the correct ellipse exposure or the right measurement.

And serious disadvantages:

  1. The photo has already been taken and there is much you don't have control over. The projection is perspective, and the distance from the subject and the angle of view have been fixed.
  2. There needs to be a lot of guesswork to be done, to figure out what smaller components exactly are. - a screw head might look like a big black blob due to light effect and orientation
  3. Orientation issue - Ever tried taking a truly 'isometric' photo of something. It is really difficult to do so in real world. Real world is in perspective. A perspective view, by its very nature, is the exact opposite of an axonometric view. Similar distances cannot be compared across a perspective view because distances appear smaller the further the distances are from the viewer due to a phenomenon known as convergence.

The way we do it!

This is the image of a roadster chassis that we are going to photo-trace. Look how dirty and fuzzy it looks!

Roadster Chassis Bitmap file to be traced

I would like to illustrate how tracing works by a small example. This is a very simple and basic isometric image. It looks very fuzzy and pixilated. It will lose it's quality if we change the resolution. That is why we are going to trace it to a resolution independent vector graphic.

We begin tracing by opening the image and placing it on the canvas in Adobe Illustrator, Corel, Isodraw or any vector program which you use. Place the image on the lowest layer and lock the layer. Locking the layer prevents the image from moving on the canvas/artboard.

Two layers for tracing

I like to dim the image by 80%, since it helps me to focus more on vector lines while tracing.

Dim Opacity to 80%

Begin tracing over the image on a new layer placed above the locked layer. It helps to focus if the stroke color is something bright like red or blue. It acts as a good contrast allowing us to visualize the output.

Magenta color strokes provide good contrast

After you are done tracing, hide the layer containing the image and do feel good looking at the stunning magic you have done just using a photograph!

Final Traced output

This is how the final image looks like. Notice the high quality, sharpness and it effectively communicates the graphic data. This is ready to be inserted into the documentation now!
There are some things to be kept in mind when photo-tracing:

  • Large, complicated pieces of equipment are prime candidates for photo tracing. For example, observe the engine pic below:
  • It would take hundreds of engineering drawings to describe all its components. Construction in perspective might take a week or longer. But with tracing, if you have an acceptable photograph, an experienced illustrator might require only 8 hours from start to finish. So the quality of photograph is inversely proportional to the time required to produced desirable output. Higher the quality lesser the time!
  • For better quality, keep Smart Guides on in AI and by extending the Cap and Join with the Rounded option, smooth lines can be

There are more advanced techniques which I use for tracing, I will add them in future posts. Thanks for reading!

Surge valve image credits: Greg Maxson and Jon Duff, The Complete Illustrator, McGraw-Hill Press