photographs of CAD drawings

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I would like to know the methodology of taking digital photographs of CAD drawings of a maximum bounding-box size of approx. 40 inches by 20 inches and sending them to the computer in real size in order to operate on them on the computer. These CAD drawings are only line drawings and they do noy contain heavy graphics. I also would like to know the particular type of digital camera suitable for this purpose.

Thanks, Devarajan

-- T.E.Devarajan (tedevraj@satyam.net.in), July 29, 2000

Answers

As far as I know, one normally uses a wide format scanner to scan the images into bmp or tiff files and then uses a program designed to turn bmp or tiff files into vector based files. I'd say the best place to start looking would be to find the bmp to vector file conversion program. The program should provide something in the way of specs concerning acceptable scanning resolutions to pick up sufficient detail to reproduce the drawing as lines or vectors. It seems to me you'd want to start looking at your CAD program manufacturer's door first. Some CAD programs have converters built into them. I seem to recall a couple of very cheap CAD programs that had those capabilities.

At any rate, capturing a 40x20" document with even a 3.3MP digicam would only yield 51 PPI (2048/40"), that's not much to work with for schematics or drawings with any level of detail. You could do better by capturing two shots and stitching them together.(102PPI)

If it were me, and I had to do a lot of them or do them over a long period of time, I'd consider buying a large format scanner or scanner/plotter combo. If not, I'd find a place that does CAD work and pay them to scan them for me. They may even have the conversion software and be able to offer you vector files.

Bear in mind, that vector files aren't the equivalent of CAD drawings made with symbol primitives. As far as I know, in the resulting vector file EVERY line segment(as in every segment that makes up each symbol, etc.) is a separate entity, so any editing that needs to be done can be VERY cumbersome. If any significant amount of editing must be done to such a file it may be simpler to redraw it -especially if the file is likely to be edited several times over a long period of time.

Lots of luck!

-- Gerald M. Payne (gmp@surferz.net), July 29, 2000.


We experimented with vectorisation programmes at our architecture practice a few years ago and were extremely disillusioned with the results.

I would say that if you are hoping to get fully editable CAD files you will be very disappointed. (ie no layers, some lines become confused, no text is editable etc.)

The 1 big advantage is that the resultant vector files are significantly smaller than their graphic counterparts.

I would agree with the comments above, try a vectorisation programme first and see if you are happy with the results first before investing heavily in any equipment.

Again as mentioned above, a consumer digi-cam will fall woefully short of capturing enough detail from a 40x20 size drawing to provide you with a useful image - any fine detail will be lost.

What do you want to do with the resultant files ? this will dictate whether it is worthwhile pursuing, and the best methods.

all the best

Martin

-- Martin Ellis (inca@globalnet.co.uk), July 29, 2000.


If they are CAD drawings, why not export them as WMF files or plot them as tiff files. No scanning necessary.

However I suspect that they are blueprints. If they are line drawings, the fastest way to deal with them is to have a redo them as AutoCad files. The amount of cleanup that you will need to do will come close to redoing the drawing originally,

-- Jonathan Ratzlaff (jonathanr@clrtech.com), July 30, 2000.


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