The most popular scanner width among CAD users is 36 in., though most scanner vendors now offer comparable 42-inch models that are only slightly more expensive. But GTCO released a new 42-inch monochromatic scanner, the LF542, for the same price as its mainstream 36-inch model.
|GTCO Calcomp ScanPlus 6 LF542|
GTCO Calcomp offers three 42-in. scanners. The least expensive is the LF542 (click here to download a small PDF on the LF542). At $10,900 with scanning speeds of 12ips (inches per second) in black and white, it offers a combination of excellent performance and low price for most CAD businesses. The others are the LF742, a 12ips black-and-white scanner with a moderate color speed of 0.6ips for $14,900, and the top-of-the-line LF942, with a top speed of 12ips in black and white and 1.5ips in color for $20,900. GTCO Calcomp series scanners have two-year on-site service warranties within the U.S. Outside the U.S., the two-year warranty covers only parts.
Softcover’s Scan2CAD Software
As the name implies, Scan2CAD is an all-in-one software application that can scan and convert a raster image to a DXF vector file. However, it also offers a full feature list of editing tools to clean, edit, and convert the raster file to a usable vector file for the CAD system.
Scan2CAD’s feature list and quality of conversion match rival applications, but it is priced to be more affordable than many. The basic version is $279, while the professional version is $469, both single-user licenses. The basic version does not have OCR (optical character recognition), batch conversion, and a few other features.
> > Figure 1: The basic scanner interface using a TWAIN driver.
Scan2CAD is currently in version 7.5g, having been on the market since 1998. Softcover International offers free upgrades within major releases and free e-mail software support.
The software can work simultaneously in both raster and vector domains. In the raster domain, it can load files from a variety of raster file formats, including BMP, PCX, TIFF, IMG, CAL, GP4, CG4, MIL, JPG, GIF, PNG, and CIT. You can also scan a drawing using either TWAIN or a WIA (Windows image acquisition) driver. With the WIA driver, you can use a digital camera to capture the image. I currently use TWAIN, which in most cases offers more control of the captured image, particularly when handling difficult drawings (see Figure 1, above) where scan parameters must be tweaked to make the image suitable for a vectorization.
A WIA driver interface offers very limited control of the captured images and is not suitable for older, faded CAD drawings (see Figure 2, below). In those cases, using optimal scan parameters is crucial for a good vectorization conversion.
When scanning using Scan2CAD, you set up basic scan parameters prior to scanning: scanning mode (such as color, gray tone, or black and white); scanning resolution in dpi; and drawing size. There is even a preset list that gives you default scanning parameters for various types of engineering drawings (such as blueprint, brown, or sepia-toned images) and maps.
While scanning or in preview mode for black and white, you can adjust scan parameters for fixed threshold, sharpening, de-speckling a hole-filling, softening, and blurring, making it easy to set optimal scan parameters.
>> Figure 2: A WIA (Windows image acquisition) driver offers limited control of scanning.
I recommend you use the TWAIN interface when scanning a traditional blueprint. My attempt shows a blueprint that proved difficult to scan. If you were to try a fixed-threshold scan, the result would be useless for any vectorization (see Figure 3, left-hand image, below).
Scanning Difficult Drawings
The TWAIN driver for the LF542 has an advanced feature called Adaptive Threshold for cleaning deteriorated drawings and blueprints. Deterioration can result from many years sitting in a drawer, exposure to light, or blue background noise on a blueprint; its effects can be minimized by selecting the Adaptive Threshold scanning mode. It’s a must when planning to vectorize or perform raster editing on the drawing (see Figure 4, right-hand image, below).
Scan2CAD Raster Editing, Cleaning, Vectorization
Before starting the vectorization process, it is important to first clean up the scanned image. Scan2CAD has powerful tools to do just that. In addition to the Smooth tool for smoothing edges and circles to get better vectorization results, you can thicken weak lines and perform all the usual manipulations: cropping, rotating, de-skewing, de-speckling and hole filling, scaling, enhancing contrast or brightness, and so on.
Figures 3 & 4: On the left is a scan of a blueprint using fixed-threshold scanning. On the right is the same drawing scanned with Adaptive Threshold. This time, the result can be used for vectorization.
After cleaning up the raster image, you can go straight for a fully automated vectorization, which is very fast. Even a difficult E-size drawing took less than two minutes on my notebook, and it created more than 163,000 vector objects. After vectorization, you can toggle between the raster image, the vector image, or both at the same time. This feature makes it easy to adjust the vectors for higher accuracy.
Vectors, although always perfect, rely on a raster image that is less than perfect. For example, an angle line in raster usually looks like a staircase. Scan2CAD has some very powerful vector editing capacities. With a few clicks, you can merge vectors and straighten the line as shown in Figure 5 (below). Also, vector lines on the right have been smoothed while the vectors on the left have been left unaltered. Scan2CAD has similar features for straightening arcs and circles.
Scanner and Raster Conversion for CAD
The GTCO Calcomp ScanPlus 6 LF542 large-format scanner represents the best value for your money. Its combination of midrange pricing, a 42-inch-wide scanning capability with fast black and white speed makes it a good choice for those who only need monochromatic scanning.
> > Figure 5: The left side shows vectors based on a low-resolution image and the right side shows vectors after they have been straightened.
Combined with the Scan2CAD application, you now have powerful tools for taking engineering drawings from your archive into a useful vector file format that you can import into your CAD system. Scan2CAD is rich in features and matches considerably more expensive packages on the market.
Henrik Vestermark is an independent consultant who has been in the large-format scanner industry since 1988. His expertise includes large format and large-format digital capture, development, sales, and marketing. He is now the president of The Other Solutions — a Web-based provider of affordable solutions and consultancy to the IT and large-format markets. You can contact him about this article via e-mail sent to firstname.lastname@example.org or to DE’s editors by clicking here. Please reference “Converting Old to New” in your message.