As well as creating parallel perspectives, phototracing is an effective technique for achieving rapid results. However, it does require more experience than other techniques.

Phototracing has various advantages:

• It produces very realistic images
• Using a photo is a fast way of creating an illustration
• Non-technical information can be included in the photo (hands, users, etc.)
• The graphic information can be reduced or expanded as required
• Troublesome shadows are eliminated

It can sometimes be difficult to start using phototracing without some guidance or experience. It is essential to take a structured approach to the task. A few important points are considered below.

Assessing your photo
Before you start tracing the photo, take a moment to look at it closely. Look at the areas which will subsequently be the focal point of the information. What do you see? What role do the photographed elements play in the picture?

Describe for yourself what you can see:
"I can see a gear lever. It has a sphere on the top. The top of the sphere has been cut off and replaced by a matching plastic part showing the position of the gears. The joints are rounded so that I can't hurt myself on them. This creates a kind of groove all the way round."

Check what materials have been used.
A dashboard is always heavily rounded and has a soft covering. There are numerous radii. These need to reflect the rounded look in the finished picture. Take a look at this picture and the radii it contains.

Make sure you understand how the parts you are depicting function.
They must be depicted so that this is readily apparent. Distorted or imprecise images can make this difficult. For example, a distorted rotary switch may look as though it wouldn't turn properly.

You can suggest radii merging into each other by means of small hooks at the ends of the curves. If you only use straight lines, your illustration will resemble an arrangement of disjoined lines rather than a depiction of an object.

Learn to use perspective properly
Cylindrical elements consist of at least two ellipses and two lines. It is important to ensure consistent perspective within such elements, and also to make sure that the element is placed in the correct perspective relative to its surroundings.

The image shows the correct perspective on the left (A), and an incorrect, inconsistent perspective on the right (B).

The incorrect view becomes clear if you look at the minor axes which have been drawn in:

In figure (A), the minor axes of the elements in question are correctly lined up, while in figure (B) they are out of line.
Remember that, when tracing a photo, a vanishing point perspective is used. This means that elements cannot simply be copied and moved to a different place.

An element needs to be depicted differently if it is moved to a different location.

In the following example, the two bolts at the top are almost identical, but their orientation is different. The distance between the two minor axes is different, (A) being greater than (B):

As the distance between the elements increases, the size, ellipse value and orientation of the ellipses differ visibly. These points must be taken into account when producing the illustration. If you ignore this theory and arrange the elements incorrectly, your illustration will lack spatial effect, and will appear flat and meaningless.

Since our daily experience of looking at the world around us has taught us to use perspective correctly, we will all judge such an illustration as poor, even though we may not be able to explain exactly why it is so.
 

Learn to use your graphics program properly
Your graphics program is there to help you with your work, but cannot do everything for you. You must select the tools and arrange the elements. Along with the ellipse, the Bézier curve is your most important tool when tracing photos.

Learn how to use it and read the documentation provided with your graphics program to find out exactly what you can do with the Bézier curve.

Soften your illustration
You may often find that you have drawn everything and got the perspective right, but your illustration still looks static and angular. The illustration is only "technically" finished. It still needs to be softened to make it look less stiff.

Lines with small gaps in them (known as inner edges) will provide the necessary softening effect.

These two images demonstrate the use of inner edges. The right-hand image clearly shows that our brains require only the suggestion of two edges on the horn plate to be able to fill in the rest.

There does not need to be a line on every edge, in fact, there should not be a line on every edge.
To assist you, take a careful look at the photo - you need to draw in the inner edges where light can be seen reflecting off an edge.

If this is not sufficient, draw them in individually using an imaginary light source. You will soon find that the task becomes easier as you become more experienced.