CAD FAQ

 Q. I have an old plan and profile drawing that was provided to us in paper form many years ago. I would like to have it in electronic form so I can use it in AutoCAD. How is it done?

The first step is to get the best quality paper copy of it and send it out for scanning. If your drawing is say a standard D sheet, (24 by 36 inches), you should not have any difficulty getting it scanned. Check the yellow pages.

Q. Exactly what should I ask for when I get it scanned?

There are three primary things to consider when doing this. These are listed and discussed following.

Optical scanning resolution

Output file format

Storage requirements

Optical scanning resolution

Typically no more than 300 dpi is required for a standard drawing. This should be adjusted upwards or downwards depending upon the condition and detail contained on the drawing to be reproduced. Scanning at 300 dpi will create a very large file and therefore will be difficult to handle on older machines. Sometimes you can get away with scanning at 75 dpi when drawings are in good condition with thick line work. We scan our drawings at 300 dpi, sometimes at 1200 dpi when their is fine linework.

Output file format

There are hundreds of file formats that scanned images can be stored in. The scanning vendor will ask which you want. The choice will be dictated by the capabilities of the software you will be using to convert the file. For example some CAD overlay prefers a very specific type of tif graphic file. Make sure that you know what type you need and that the vendor can provide the required file type. If they cannot, then you will need software that can convert the file into the appropriate type for you. There are many such shareware and freeware products that can be downloaded from the Internet. Tif files are great - however make sure you choose the correct flavour as their are hundreds of tif file formats out there.

You will usually want at least a colour scan in 256 colurs, monochrome scans can be used when the drawing is not detailed.

Storage requirements

The scanned files will be very large and you will require some kind of large storage device to transfer the image from the the vendors business to your computer, particularly if you are doing lots of them. Pick a vendor that uses rewritable CD's. This way you can buy a CD once for say $10 and use it many times for each drawing you do. Better yet choose someone that operates a BBS so you can download over the phone. Alternatively you can download from the vendors web site but scanned drawings can be very very big.

Q. What happens next?

In the case of CAD overlay software, it must be properly configured to run with your version of AutoCAD.

Q. Can't I use a non CAD based product?

Yes there are non CAD based solutions. For example a GIS based software package like MapInfo can be used. However chances are you might not have that. Other packages like CorelDraw can theoretically be used, but you will have a very difficult time getting acceptable results when you try to transfer the completed vector image from CorelDraw into CAD. The bottom line is that you'll need software that will permit you to trace over your existing drawing and save it in a CAD format.

Q. I've read the CAD manual and it says I can bring in scanned images. Why can't I just do that?

Your right it says that. But the reality is that CAD is not able to bring in large scanned images. Give it a try if you want.

Q How exactly do software conversion products permit you to create new drawings?

These products permit you to bring the image into CAD or near CAD environment and permit special functions for example:

as you trace elements using the software tools, the area that is traced is erased from the scanned image, permitting you to monitor your progress.

special tools also become available, for example the ability to snap to a bitmap point

Q. So you just trace the objects on screen?

Yes. The objects are traced manually by the operator and the elements and text can be placed onto appropriate layers, lines snapped to each other etc. Blocks can also be inserted as you progress. An example of a completed drawing.

Q. What about automatic vectorization of drawings. I've heard it works?

Yes it works to a limited degree. However the software technology still does not, and may never come remotely close to providing the kind of quality product that manual re-creation provides. For example text, a major component of many drawings is still very poorly recognized by software and the time involved in checking and correcting errors is better spent in our opinion in just doing it. This also provides the opportunity of correcting errors that may be on the original.

As a bonus, manual conversion also enables the drawing to be converted into metric units.

CAD files that have been simply vectorized can be several hundred times larger than those done interactively as we described above. When you attempt to edit these drawings, instead of simple changes taking minutes, they can take hours, sometimes the machine will simply hang.

Q. How much does it cost?

The price will vary from company to company. Sometimes it will be difficult to compare prices - apples to apples as they say. Quality is largely a function of the CAD operators performing the work, and their experience in the field of work related to the CAD drawing (ie mechanical, civil). We recommend you verify what each vendor you talk to provides as an end product. DART provides 100% true layered CAD files. DART's workers have an extensive background in CAD, and therefore aware of the needs of your ground floor CAD users. Simply put DART provides exactly what would have gotten from the designer originally. For an online anonymous quote click here.

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