How to Modernize Your Paper Engineering Drawings
A White Paper From the Paper to CAD Experts
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.
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.
© Copyright 2017 GTX. All Rights Reserved.
GTXScanClean™ is protected by U.S. Patent No. 7,016,536
GTX Europe, Ltd. •
Unit 9A, Intec 2 •
Wade Road, •
United Kingdom RG24 8NE •
tel: +44 (0)1256.814444 •
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Company: GTX Europe Ltd. •
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Place of registration: England)
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