By Chris Miller

Cad Services Manager, Autovectors.com

Of all the technologies that have or can improve the life cycle of drawings within the realm of design, drafting and geographic information systems (GIS), none has offered more promise than to convert raster scanned old drawings into the desired format of CAD or GIS tools, vector. However, with paper based archives growing at an astounding rate of 26 million new drawings per year, and CAD representing 20 percent or fewer of a company's information assets, why haven't the associated technologies been embraced?

Over the years, CAD and GIS have proven themselves as necessary tools for manufactures, architects, engineers, planners, etc., reaching a point of necessity for a company to compete with quality products and improved delivery of goods and services. Unfortunately, the integration of those dirty old paper drawings has not been an easy process, or one as clear-cut as vendors preach

and end users desire.

The issues surrounding the bridging of a corporation's two most valued assets, information and information processing, have never been more misunderstood. This paper looks at the technologies, techniques, and cost justification factors to bridge these corporate assets together.

Beginning

The process of converting paper based archives into the CAD environment can be best modeled as one of transitions and needs. First, a paper drawing is converted into an electronic form by a scanner. Then CCD Cameras or array's take the paper into a compressed raster digital image of unintelligent dots or pixels. At this point, the electronic drawing can be enhanced and stored within a controlled document management system, such as "SCAN-ARC".

Scanning Basics

Our scanners produce raster format files which include a series of black or white pixels or dots. The accuracy is often measured in dots per inch (DPI) and include typical resolutions of 200 or 400 dpi. When a document is scanned, it is viewed as a series of greyscale levels which a scanner will threshold to either a black or white pixel. This process is often referred to creating a binary image. With our Image-Logic features we are able to perform many additional, on the fly, functions to enhance and cleanup drawings , such as with despeckling.

Once threshold, the scanned drawing can be saved in any of a variety of raster formats including TIFF, CALS Group 4, or various RLE formats. Data compression techniques have emerged in the market to allow raster based drawings to be stored in less storage space than a native CAD file. This is due to the use of two dimensional compression which can reduce an 8MB uncompressed raster file to approximately 100kB without any loss of information. The most popular formats found in the market today are the CALS raster and TIFF format, both utilizing the group 4 compression method.

Lower storage costs have also added significantly to the cost benefits of scanning. Storage costs have continued to diminish to the point of affordability for handling complete archives of company's drawings. Rewritable and WORM (write once, read many) optical technologies configured within jukebox systems now make it possible to place hundreds of thousands to millions of drawings on-line.

While scanners produce unintelligent raster files, most users are familiar with the benefits of a vector/CAD environment. While the "religious war" between these two formats continues, it is raster and hybrid environments where the benefits of both raster and vector based systems are best realized. Some of the leading tools today even behave much like CAD allowing complex selections of raster geometry.

Raster is best suited for capturing a company's archives into manageable files that are well suited for simpler drafting modifications. Vector/CAD based systems provide easier editing and are best where modeling and analysis are required. To utilize the CAD system for all documents, however, requires the added costs of converting the raster information to vectors.

What is the quality of your originals? A significant differentiator with leading scanners is in their ability to handle poor quality drawings. This led Action DIS to obtain a device that includes adaptive and linear thresholding where varying enhancement techniques are used to process a drawing with ever changing quality.

What is the density of your drawing? This issue will determine the maximum resolution required for a company's needs. The most common resolution is in the 200/400 dpi range, but some applications can approach 800/1000dpi resolutions.

How do you maintain quality of the scanned images? This requires operators to view the scanned images. This process will probably control the throughput of scanned drawings.

What are your throughput requirements? Affordable in-house scanners may offer one 90 seconds or more. Sending to a service bureau could cut time of getting large sets produced by more than 80 percent.

How much additional database information is needed to incorporate scanned files into your existing system? In most cases the viewing of the tif file for collecting database information is the same for a file from a service bureau as it is for drawings scanned in house.

In house or out source scans to Signature Designs? There are significant advantages to companies looking at incrementally implementing "SCAN ARC" by using Signature Designs whose expertise and equipment is available. This affords a smaller company and pilot systems or larger companies an affordable method of capturing their paper archives.

Plan Globally, Implement Locally

The most successful implementations of scanning solutions are those which are planned globally but implemented locally while focused on a specific and justifiable business issue. Once expected productivity has been attained, companies can incrementally expand to a broader implementation:

Most companies prefer to convert paper archives into the proven CAD environment where electronic drafting was first introduced to their business. This approach can take additional time to convert the raster images to vectors due to the complexities of the process and the often poor quality of original drawings. However, once converted to vector, the cost of savings can be large when considered over the life cycle of the drawing.

Often called "hyperlinking," an emerging alternative is the use of raster images and hybrid raster/vector editing and maintenance tools that take advantage of CAD's modeling and analysis benefits with the cost effectiveness of scanning and preserving drawings libraries by simply pointing and clicking on the appropriate element for which they desire more information. This search method can replace the sometimes tedious method of keyword searches.

While CAD conversion and raster/hybrid editing are focused on improving individual productivity, scanning paper drawings can provide improvements to a company's business process. A fully implemented database system can help reduce product cycle times and produce lower cost by addressing business process issues related to design release management, document storage management, ISO 9000 compliance, and more.

When drawings become active within the design and drafting environment, changes can be incorporated and a new revision or an updated as-built created. This process is where most confusion exists and the opportunity for success or failure is greatest.

There are three distinct methods of updating old paper drawings using scan-conversion based systems. The are (1) raster drafting or enhancement, (2) raster-to-vector conversion, and (3) a hybrid approach. All methods have their place in most organizations influenced by the following factors:

Your application (GIS, mechanical, AEC...)

Revision frequency throughout the drawing's life expectancy

Your expertise and availability with raster or vector tools

Modeling or analysis requirements

To many, a religious war has existed between staying in raster or converting to vector. In looking at the hierarchy of the engineering archive, three distinctive environments have emerged where raster and vector systems apply. Most information is maintained in an archival state representing older and obsolete designs within a company. These are best suited for a raster environment due to the economics involved. Once within an active revision cycle, drawings can be handled in either a raster or vector environment for the design and drafting environment. At the high end of corporate value are drawing requiring modeling and analysis to them and can only be handled by vector based drawing.

The Raster Drafting Process

Raster editing or drafting is the simplest and most productive way to modify scanned paper drawings. It incurs the lowest cost to enable the drawings into a format where changes can be made. This is supported by the availability of many service bureaus, and the recent price breakthroughs of large format scanners. Raster drafting works best when simple updates are required in nondimensioned or analysis-oriented drawings.

There is significant differentiation with the products found in the market today in terms of feature functionality and positioning. The more advanced systems are capable of snapping to or selecting and manipulating raster "entities," just like vector CAD entities. Some packages are specifically positioned for niche applications, like mapping, where distortion correction is required to update drawings to world coordinate systems.

The autovector process

Drawings with the highest degree of corporate value are those used within analysis and modeling systems and are required in a fully vectorized format. For instance, a company may need to develop a 3-D model from an old drawing and run FEM or interference checks within the model. Or a city planner is looking at developing a new structure and requires using 3-D terrain models from old paper drawings. Both environments require vector CAD models in its purest form and consequently require the full conversion to vector. The tools to accommodate this are:

Match conversion tools, which work with a set of predefined rules to accommodate unique settings like text classification, width separations, and types of entities to recognize. This works best when drawing quality is very good, drawings are consistent, and the desired result is basic primitives. The results of batch systems will often require cleanup to rectify the results into the desired results.

Manual tracing, which, although very labor intensive, still has its place for converting drawings that have very poor legibility and cannot be used with automated techniques. Using raster snap techniques and heads-up digitizing, this method offers improved throughput and accuracy over traditional hand digitizing methods still widely used by many companies.

The Hybrid Process

The most promising of the conversion techniques joins the intuitive knowledge of the user in an interactive line-following or selective process, or raster/CAD environment. These tools allow an operator to work with the limiting factors of the technology, while realizing the productivity gains provided by inexpensive raster scanning. As an example, a topographical map is converted by selecting a raster contour, the software vector traces it to an intersecting or gap position. The process is completed for the entire trace, and an elevation assigned to make it a 3-D model for the GIS systems to take over.

Another approach, and one which works best on facility or mechanical details, is a selective conversion process. Under this method, raster areas and elements are manipulated within a raster selection set. From that point, the selection set is auto-vectorized using a unique set of rules like applying orthogonal rectification, conversion to line styles, or even raster smoothing. Again, the advantages of man-machine working together creates an efficient process with savings over manual or batch only alternatives.

A fully hybrid approach is one where raster and CAD information are maintained for a drawing. Changes can be made to either environment and information exchanged back and forth between the two thus offering the most efficient manner for modifying the old with the new.

Cost Benefit Analysis

Cost justification of the technologies described in this article is based in labor savings in the drafting process, improved time to market, and better management of the data. In looking at a life cycle model first appearing in Document Management magazine, each technique has an inherent cost associated with initial capture of the archives (scanning and conversion), and a cost associated with implementing revisions throughout the drawing's life.

Vector/CAD drafting offer the most cost effective method of modifying drawings and can't be beat for those drawings already in CAD. Of the scanning methods, raster or hybrid drafting and raster-to-vector conversion will attain a break even at anywhere from one to one revisions over the life cycle of the drawing.

While a break even of drawing revisions will be dependent on many factors, it is clear that a trade off of investing in the up front conversion to full CAD versus taking advantage of lower cost hybrid and raster systems is the crucial issue for companies to consider when looking into the economics of the conversion effort. Now is the time for companies to take control of their paper assets and utilize proven tools to make their products more timely and competitive within today's market.

Chris Miller is the CAD Services Manager with Signature Designs, which specializes in document and system management for companies implemented Internet, Intranet, and file manipulation systems, for archiving or editing new and existing raster/CAD files. Mr. Miller can be reached at the following 770-439-9383