Re: Scanned drawings and CAD

Paul Butler (
Tue, 8 Aug 1995 08:20:30 +1000

Hi All

While searching for something else, I discovered what appears to be a very
useful shareware utility for use with CAD systems. It is a program that converts
PCX scanned images into vector DXF files, which can be imported into many PC
based CAD programs.

The program is within a ZIP file called
and I retrieved it from the SimTel Software Repository under MSDOS/autocad
using the LYCOS search engine under NETSCAPE.

If you want to ftp the file direct, the address is:

The program offers a number of filtering controls and basically it seems to be
drawing lines through each horizontal row of pixels.

I tried it out last night on a 600dpi scan of the the left fuselage side of the
AGO C.IV at 1/48 scale. This drawing can be found in Windsock Vol9, No6 Nov/Dec

I was impressed with the result when I imported the DXF file into AutoCad LT 2.
The image was clear, and with due deference to the difficulty in using the
poor spline drawing tools that AutoCad provides, it should not be difficult to
use such images as a starting point for model plans. In the past, I have used
CorelDraw 3.0 for this purpose and then exported the Corel drawing to the CAD
as a DXF file (which can be huge because of the large number of DXF elements
created to represent curves).


The DXF files produced are VERY large. Apparently the registered version of the
program is a bit more economical in this regard. For example, the DXF file for
the AGO drawing was over 200000 bytes (can't recall the size of the original PCX

My computer is a 66mHz 486 DX2 with 8meg RAM, 24meg virtual memory, fast IDE
hard disks (750meg in total), 32bit VESA acelerator video card (with 2meg
onboard RAM) and
32 bit VESA disk controller card. The performance was satisfactory with AutoCad
LT 2.0 which is a Windows program. You might have difficulty with a lesser m/c
unless you use a DOS CAD program like Generic Cadd 6.0 (which is fast) and
perhaps do some filtering of the image. You could scan at a lower resolution
than 600dpi and perhaps have the conversion program ignore every second line or
so. This will significantly reduce the size of the DXF file.

BTW Generic CADD is more that adequate for drawing model plans, if fact better
than AutoCad LT in many ways, (it has decent bezier curves for one thing), but I have migrated to Autocad LT because AutoCad is an industry standard. It is also
a bit faster to use on my m/c than Generic Cadd. Generic Cadd doesn't appear to
be much slower on a 25mHz 386 m/c which I also have.

Of course, all of my earlier comments about scanning images still apply if you
want to use this technique for producing model plans. I have found that it takes
at least one hour to do a careful scan of a drawing like the one mentioned using
a flat bed scanner. To minimise the problems you will have at the CAD drawing
stage, you must take care to get major axes, like the engine thrust line,
to with a pixel or three of the major orthagonal axes of the scanner. You must \also scan each component separately. Do not simply scan the entire drawing in
one go because you will be disappointed.

On final word about scanners; don't try and do this with a hand held scanner,
they are useless for the task. Beg, borrow, hire or buy a flat bed for the job.
The low cost Hewlett Packard 3P should be more than adequate for the job.

I have not tried this technique with a colour scanner yet and I am not confident
of the result because many colour scanners use oval pixels which might introduce
unwanted distortion. I have been told, but not confirmed, that the HP 3C uses
round pixels like the B&W scanners.

If anyone would like to try this, I would be happy to hear from them.


Paul Butler