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Compare technical drawings in your home office?

Compare technical drawings in your home office?

by Gerald Keil

This article is about advanced possibilities, in the office as well as in the home office, to quickly and reliably recognize the differences between different drawing versions in order to derive the appropriate measures for your process.

The advantages of electronic comparison of drawings:

Printing or plotting of drawings for comparison purposes is no longer necessary

All necessary information is contained in a single PDF document

Even on large drawings, you can see all areas where something has changed from a bird's eye view

When zoomed, you can see the detailed changes either in the Difference View or by switching between the original documents using the PDF layer technique

The numbering of the areas and a coordinate grid help to document the changes

Engineering in the home office?

There is an unmistakable tendency to move construction work to the home office. Nowadays, a lot can be done electronically - just think of powerful CAD laptops or high-performance access to CAD hardware in the office. In practice, there is a powerful CAD machine under the desk or in the server room, but useful alternatives for the home office are still rare. An average equipped laptop alone is certainly not the solution.

Compare drawing versions in the home office?

The comparison of drawing versions is undoubtedly also part of everyday life in the field of design and engineering, in order to completely record changes made by customers, suppliers or the company's own design department. With A4 drawings this is still quite easy to do electronically. With larger formats - ISO A2 and larger - this is usually more difficult.

It is certainly not an ideal solution to print out the drawings at work, take them home with you, hang them next to each other on the bedroom cupboard or stick them on top of each other on the patio door with transparent adhesive tape to discover the differences in the backlight of the morning sun - equipped with a pot of coffee and a few stickers.

Apart from the doubtful preparation effort, neither the boss nor the flatmates are really enthusiastic about this method.

Rather more acceptable would be a solution with which, with a normal laptop and the generally available Adobe Reader,

1. one can very quickly and reliably identify all areas in which changes can be found at all, even on large-format drawings (where are the changes?) and

2. that allows you to zoom into the documents with the option of viewing the details of the first drawing, the second drawing or the overlaid drawings (what has been changed?)

What is the scenario like, for example, with a contemporary Difference View in PDF format in the office or home office?

What is a „Difference View“ anyway?

A Difference View is a common PDF document, which - placed on different layers - contains the drawings of both the previous and the current version and the overlapping of both documents. With Adobe Reader, these layers can be shown and hidden in a targeted manner:

Where can I get the Difference View?

There are two basic ways to make the Difference View available:

a) automatic creation in the background

Such a Difference View is automatically generated on a company server on a specific event. The release process of the current version is often a good time to have a Difference View generated in the background and make it generally available in the PLM or document management system. Whichever department is involved in the change process - the Difference View is already there and can be used at any time.

b) interactive if required

With the help of a web interface, every employee can have a Difference View created ad-hoc by himself, if he has a connection to the server. Even in the home office. This may take a few seconds - but you can compare any versions with each other. The result can be displayed directly in Adobe Reader after generation.

How do I find all changes at a glance?

Using the Difference Mask, all areas where changes have been made are highlighted. Especially for large drawings and for a few small changes this is a great help. However, the Difference Mask can only be displayed if the drawing versions are sufficiently similar.

The numbered areas allow a systematic analysis of the differences. You can also refer to them, for example in a separate change description.

Through the Difference Mask you can even on a laptop view an A0 drawing from a bird's eye view and see all changed areas. Home-office capable.

What do the changes look like in detail?

Now you can view the changed areas one after the other. With the integrated zoom tools you can dive into the area and analyze the changes in detail.

Instructions on how to set up the Adobe Reader optimally can be found here.

Text changes in particular are often hardly recognizable due to a blue-red pixel mix. This is where the PDF layer technique comes into play. In the Difference View, the two original documents are additionally stored on separate layers that can be switched on and off (see picture above). Since the details of all three layers are exactly on top of each other, you can switch back and forth between the layers even when zoomed in and view changed texts, parts list tables or tolerance specifications before and after without the irritating difference information. Suitable for home office use.

What helps me to document the changes?

Finding and evaluating changes is one thing. Documenting the changes for subsequent processes is another.

If you like, you can use the purple area numbers to target the changes in your actions or reports, for example "#3: diameter changed from 10 to 12mm".

In order to address specific areas of drawings, it is traditionally customary to label the edges of the drawing frame with 1, 2, 3 etc. at the top and bottom and A, B, C etc. at the left and right. This allows the fields at the intersection to be clearly addressed, for example with "D8". However, this is problematic with large drawings in the home office. Either you can't see any details in the overall view or you are zoomed in in the middle of nowhere.

At this point, an optional coordinate grid can be displayed. These grids are created for A4 to A0 and then made available in the Difference View depending on the format. So you always know where you are - even if the drawing borders with the labels are no longer visible. You can write "C3/D3: diameter changed from 10 to 12mm". This detailed solution is of course also ... (well, you know already).

Unfortunately, despite ISO standards, in practice there are many different field divisions, so that the coordinate grids usually have to be adapted to company-specific requirements.


With the right tools, you can not only make better use of the advantages of digitization in the "engineering office" by dispensing to print out your drawings, but rather to identify all version changes reliably and quickly. Even your bedroom cupboard remains usable for the important things and you don't have to worry about Tesafilm leftovers on the patio door anymore.

Dr.‑Ing. Gerald Keil   //   Engineering with passion

With this blog, let us learn together from innovative companies.
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