Desktop Engineering test Calcomp's ScanPlus with Scan2CAD

Henrik Vestermark looks at the combination of GTCO Calcomp’s ScanPlus 6 LF542 scanner and Softcover’s Scan2CAD raster to vector conversion software. This article first appeared in Desktop Engineering's Elements of RP&M/Reverse Engineering (23rd January 2007, USA).

Converting Old to New

Your company has a new CAD system and several 1000 old engineering drawings representing years of intellectual property. Your challenge is to store all that knowledge for re-use by the new CAD system.

Do you scan and convert those drawings or do you redraw them all?

Because of advances in scanning technology and new raster to vector conversion software that is less expensive than it once was, choosing to scan and convert your existing drawings makes more sense than ever. One solution is to combine a large-format scanner from GTCO Calcomp with affordable yet professional Scan2CAD raster-to-vector software from Softcover International.

GTCO Calcomp ScanPlus 6 LF542

GTCO Calcomp updated its entire scanner series with eight new scanners in August of 2006 ranging in size from 25 in. wide to 54 in. 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.

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 US. Outside the US, the two-year warranty covers only parts.

(Editor's Note: GTCO Calcomp scanners are, in fact, manufactured by Contex. AS Calcomp scanners are not generally available in the UK, British readers wanting something similar can see a list of Contex OEM scanners and comparable models in our November 2006 article: THE MARKET: Contex, GTCO Calcomp and Vidar equivalent models explained).

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.
GTCO Calcomp TWAIN Interface
Figure 1. The basic Calcomp scanner interface using a TWAIN driver.

Scan2CAD's current version is 7.5g. It's been on the market since 1996. Softcover International offers free upgrades within major releases and free email 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 3, below) 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.

GTCO Calcomp WIA Interface
Figure 2. The basic Calcomp scanner interface using a WIA driver.

TWAIN Scanning

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. The WIA driver offers limited control of scanning.

I recommend you use the TWAIN interface when scanning a traditional blueprint. My attempt below shows a blueprint that was difficult to scan. If scanned it on a WIA fixed-threshold, the result would be useless for any vectorization (see Figure 3, below).
Dirty Blueprint, Fixed Threshold Scan
Figure 3. A dirty blueprint scanned with a fixed threshold setting. This is absolutely no good for raster to vector conversion with Scan2CAD. You can't see any detail.

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).

Dirty Blueprint, Adaptive Threshold Scan
Figure 4. The same dirty blueprint scanned with adaptive thresholding. Scan2CAD will give good raster to vector conversion results from this. Like you, Scan2CAD can now see real drawing detail.

Scan2CAD Raster Editing, Cleaning, Vectorization

Before starting the Scan2CAD vectorization process, it is important to first clean up the scanned image. Among Scan2CAD's tidy-up tools is Simple and Adaptive Thresholding.

Typical Scan
Figure 5. A drawing scanned in portrait mode as opened in Scan2CAD, before rotation, cleaning or vectorisation.

Scan2CAD has powerful tools to do this to smooth edges and circles to get better vectorization results.

Rotated and Despeckled
Figure 6. The same drawing in Scan2CAD, now rotated, despeckled and smoothed prior to vectorisation. Shows Despeckle dialogue box with slider bar.

You can automatically thicken weak lines, fill hoes in them and perform all the usual manipulations: cropping, rotating, deskewing, despeckling and hole filling, scaling, enhancing contrast or brightness, and so on.

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. 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.

Figure 7. Detail of the same drawing in Scan2CAD, now vectorised with OCR.

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 lines. Scan2CAD has similar features for straightening arcs and circles.

Vectorised
Figure 8: The left side shows vectors based on a low-resolution image and the right side shows vectors after they have been straightened.

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.

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.

END

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.

Henrik Vestermark

The Other Solutions,
866 E Tuweep St
Meridian, ID 83642
USA.

Phone: +1 208 887 4780
Cell: +1 571 276 4050
Skype: henrikvestermark
Email: hve@theothersolutions.com
Web: http://www.theothersolutions.com

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