Thomas Schwarzer is a technical editor at commatec, a service provider for technical communication in Gießen, Germany. As an electronics engineer, he has been with commatec since 2006 as a project lead for the creation of documents in the areas of medical devices and mechanical/plant engineering. His earlier professional experience includes documentation related to products on drive technology and heating technology.
Illustrations based on 3D CAD data
Almost all products are designed using 3D CAD programs today. However the data created is seldom utilized in technical writing, often for cost reasons. Another reason is the lack of technical knowledge about the technology with which the 3D illustrations are created. This article explains two ways of how 3D illustrations can be used in technical documentation, and gives an example each from medical technology and plant engineering.
Both ways are based on CAD data from design. However the way the data is processed further differs significantly depending on the budget and required quality of the target files. The paths have already been tested in practice in projects: Version A for high value device documentation of a medical device, the more cost effect version B for plant documentation.
Version A – 3D illustration
CAD data must be available in an exchange format such as STEP or IGES for this version. This raw data was processed by an experienced 3D technology graphics expert in several steps for the practical project for a medical device. The end result were photo realistic images in TIF format, which were used in the manual. The graphics expert could rotate all or individual objects as required, define the surfaces and control the brightness and contrast settings.
Depending on the effort that can be invested, it is possible to achieve a quality of images that cannot be differentiated from photographs by most users. Unlike a photograph, the product does not need to be available in its final version when the image is created, which is definitely an argument in favor of the illustration during short development cycles. There were two more reasons to go the way of 3D illustration in our project:
- Existing manuals had primarily been illustrated with isometric or 2D line drawings. These require a small step of “translation” towards the real device by the users’ minds. Users without technical knowledge accept line drawings only to a certain extent.
- Since animation films were already planned for marketing purposes using the 3D data, the prepared data could be used jointly.
Image 1: Example for an isometric representation for how it was used for preceding products (Version A).
Version A - Process and tips
The raw data in STEP format is converted in the first step and cleaned of superfluous objects in 3D software. If components, parts from vendors for instance, exist as separate STEP files, they must be added to the entire group. Missing parts, such as outsourced items must be reconstructed in 3D.
Once the base data is complete each object is assigned surface properties in 3D software, e.g. Maxon Cinema4D or Autodesk 3ds Max. The type of light source and the positions of the lights are then defined. Individual areas need to be illuminated with additional sources of light in some images, so that these areas do not appear dark, because they are in the shadow of the defined standard sources of light. The files are subsequently rendered as so called previews with a resolution of 300 dpi. The program Mental Ray is appropriate for this process, for example. The graphics expert delivers the previews to the technical editors for a check. Once the previews are approved, the images are finalized. This means, the graphics expert improves the brightness and contrast, adds shadows, evens out colors and cleans up where necessary.
Image 2: New 3D illustration of the same component (Version A)
Version A - Recommendations
The following is recommended for using 3D illustrations in technical documentation:
- Specify with the graphics expert before the beginning of the project: How much photo-realism is necessary? Which colors should be used and how? What dimensions should the images have? How are movements shown? How are objects highlighted?
- Submit the first sample images to a larger committee for approval, before many illustrations are created in the selected style.
- Provide the most definite specifications possible for the illustrations required: Text alone is hardly suitable for conveying information about images. Better: Provided photographs of a device prototype or images of earlier products with comments. PDF is suitable for this task. Even better: a video conference to see the images together on the monitor with external graphics experts.
- Check the first previews thoroughly to ensure that all objects relevant to operation are available in the base data, e.g. the small lever found below a flap and required only for a specific maintenance task. This saves subsequent work on base data with possible impact on the previews that have already been completed.
- Mark the TIF-files with XMP-metadata to be able to differentiate final files reliably from previews. We have consciously selected identical file names in the practical attempt, to allow exchanging referenced previews with their final version without any problems in Adobe FrameMaker.
Image 3: Representation of steps in 3D illustration (Version A)
Version B - 3D screenshots
Our second version is based on screenshots prepared with the help of a 3D-Viewer. It is therefore much simpler, since the technical editor can prepare the screenshots himself, and the collaboration with an external graphics expert is not required. The results cannot be compared with professional illustrations, but then that is not the objective at all. The images and details are intended for experts, in our case for the operations and maintenance personnel. The important advantages of this method lie in the quick and economical realization. Compared to photographs, it has the additional plus point of being able to clearly map large objects such as a hall sized plant.
Image 4: Example for a 3D mapping based on screenshots (Version B)
The plant manufacturer provides the CAD-data in an internal exchange format DXF in AutoCAD, but all other proprietary CAD formats are also possible. The only prerequisite is that a license-free view is available for the format as far as possible. The viewer should also allow rotating, moving and hiding selected objects or even making them transparent. Moreover the viewer must be able to save views. In our case, we use the program AutoDesk Design Review.
Version B - Process and tips
Even though this method appears trivial, a design process saves time as well in this case. Before the technical editor begins creating many screenshots from different perspectives, he should think about which perspectives are appropriate for most of the required images. He should save base perspectives as views in Viewer to show several images from the same angle. It is obvious that the editor should select a very natural perspective corresponding to the visual angle of the user. It is also advisable to save the views from which screenshots were created. In case changes are made later, there is a defined starting point.
Version B - Recommendations
The compact but loss free format PNG is recommended for saving the screenshots. The PNG screenshots are imported to Adobe Illustrator, to apply position lines there and to reduce them to previously defined image size. In spite of the shot with just 96 dpi, a resolution of 200 dpi for an image width of up to 13 cm can be realized by scaling (without recalculation) which is sufficient for laser printing. Even objects missing from the CAD data or roughly modeled objects of outsourced parts can be added in Illustrator, e.g. switch, keys or control displays. However, this perspective post processing is time-consuming and naturally has to be completed again for every changes perspective. The completed Illustrator-files can be referenced directly as EPS in layout program, in principle. Since we were using Microsoft Word for the plant we were documenting, we decided to save the files in PNG format due to the greatly reduced file size, and to insert and link them in Word. Performance of Word does not have problems with the typical file size of between 100 to 300 KB for the 3D-images. The instructions illustrated in this manner have a volume of about 150 pages.
Summary
3D illustrations convey a photo realistic impression and are found to be more expressive by many as compared to line drawings. The type of representation is optimally suited for product representations. To some extent it is difficult to position movement arrows clearly at a component part to show maintenance tasks. For future projects we are considering reducing the degree of photo realism in favor of better options for highlighting. The limits of this method are reached when it concerns showing the same tasks for different component parts, e.g. cleaning. Like photographs, the images are so concrete that a separate image is usually required for each component part.
The image quality of 3D screenshots is not comparable in any way. However the plant operator found the technical documentation with the screenshots to be so positive overall, that it can be considered for other suppliers as reference document. For similar costs, the only alternative would have been creating few drawings, i.e. 2D overviews and representing details and work steps with separate photographs. The 3D screenshots are a better alternative in comparison, especially when during completion of the documentation a part of the plant had already been assembled and could be photographed.
Links to version A
- http://de.wikipedia.org/wiki/Standard_for_the_exchange_of_product_model_data
- http://en.wikipedia.org/wiki/ISO_10303