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How to Modernize Your Paper Engineering Drawings
A White Paper From the Paper to CAD Experts

Getting Started

It Starts With a Scan

Scanning is perhaps the most overlooked factor in the conversion process. Scanning archives into compressed raster format allows them to be enabled for faster revisions and improved distribution. This process can be painless and cost-effective. Good separation of text, quality line representation and smooth raster geometry are also important aspects that should be considered in more detail when selecting a solution. Conversion to full vector CAD format is the most sensitive to a well-scanned image.

What is a Scanner?

A scanner is a device that makes electronic images of documents. It is much like a photocopier, except that it produces electronic copies of drawings instead of paper.

How Does It Work?

A scanner contains an electronic camera and a light source. The drawing is fed through the scanner and the details are seen by the camera which then creates an electronic file. This file is called a raster or bit-map file. Much like a photocopier, a scanner has a threshold, or contrast setting. This is adjusted to produce the best electronic "copy." Usually a test scan is done to make sure that the threshold setting is good for the entire drawing, i.e., the faint lines are visible and the strong lines are not too dark.

The accuracy of the scanner is measured in Dots Per Inch (DPI). This is the number of pixels or dots that the scanner sees for every inch of paper. The higher the DPI, the more dots that are produced, and the more accurate the scan is. Typical resolutions are 200, 300 or 400 DPI. The higher the DPI setting, the larger the resulting electronic file will be. Some scanners have the ability to interpolate or expand the scanned DPI to very high resolutions. It is important that the true optical resolution of the scanner is high enough for each particular project. Most archival and raster applications are best served at 200 DPI.

There are many types of scanners that are capable of scanning A to E size paper (and larger) or aperture cards. When choosing multiple platforms, look for common user interfaces and for an intuitive look and feel.

Raster File Types

There is a wide range of standards and formats for raster files. File types can be split into two broad types: compressed and uncompressed. Some common file formats are Group 3, Group 4 and TIFF Compressed. Common uncompressed formats are PCX, RLC and TIFF Uncompressed. There are also several standards used by government and military organizations, such as the CALS standard created by the DOD and used through commercial industry. These standards are usually applied to existing formats, producing file types such as CALS Group 4.

Compression Methods

Data compression techniques have emerged in the market to allow raster-based drawings to be stored in less space than a three-dimensional CAD file. This is due to the use of two-dimensional compression that can reduce an eight MB uncompressed raster file to approximately 100KB without any loss of information. The most popular formats found in the market today are CALS Raster and TIFF format. Both use the CCITT Group 4 compression method.


A viewer is a software package that allows you to look at documents without having to use the application that created them. Viewing technologies offer a natural approach to integrating paper archives and CAD in a distribution function. In many cases, companies already maintain an active non-graphical database of drawing revisions. This database can be leveraged and "viewer-enabled" to provide the graphical link between paper and CAD-based designs. As progress is made toward EDM/PDM, the viewer can be integrated at an API level for direct communications with EDM/PDM systems. Introducing a viewer is a simple and inexpensive way to link scanning with the ongoing build of a total solution. A small investment in a powerful viewing software package offers immediate benefits with little capital outlay and minimal training time. The right viewer can help increase access to information, speed up time to market, streamline workflow, comply with ISO 9000 and OSHA standards and review and process change requests rapidly.

When selecting a viewer, look for speed, simplicity and the ability to view multiple formats. The Engineering Change Order/Engineering Change Notice (ECO/ECN) process can be improved by introducing users to the concept of redlining and integrating redline annotations on all drawings (Raster and vector CAD-based) that are now contained on-line. More sophisticated editing systems can use the approved redlines as tools to facilitate accurate and timely revisions. As workflow is introduced, the process is enhanced further with a more controlled approval procedure.

Coming Together, Raster and CAD

With a scanned drawing, revisions can be made through raster or hybrid-enabled drafting within a CAD system. The result is increased value from CAD, even before a full EDM/PDM system is in place. As EDM/PDM is implemented, full management of the ECO/ECN process will be realized.

Raster Versus Vector

CAD Systems use vector files and scanners produce raster files. What is the difference? Raster files are fundamentally different than vector files. A line drawn with CAD software is stored as a vector primitive. The software knows the starting and ending points and the line thickness. The line is "intelligent" because any part of the line "knows" that it is part of the line and what the rest of the line looks like. When a drawing is scanned, it is broken down into row after row of dots or pixels. A scanned line is "dumb" because it is made of dots or pixels forming the shape of a line. There is no information or intelligence associated with the pixels. The dots do not "know" that they are part of a line. In order to modify scanned data as CAD data, it has to be made intelligent.

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GTXScanClean is protected by U.S. Patent No. 7,016,536

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