converting old drawings

huangyhg

converting old drawings
i am doing an addition/renovation project on a 1963 building. i am just daydreaming here... but it wouldn't be great if:
i could take a scanned image of the original drawings...
pull up the negative of it...
adjust the color and contrast to gray scale...
erase some extra information...
insert it into cad very close to scale...
and draw my new framing on top of that image in cad.
i am not afraid of drawing the existing conditions... i just thought maybe someone had a more novel way of doing this.
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i thought certain reprographic companies did do digitizing of old drawings through scanning.
inserting scanned images into cad is simple enough, it's the 'erase some extra information' that is the difficult bit.
perhaps removing the additional information prior to scanning is an option, using white-out for example.
you want software that will convert raster to vector. i searched the forums with keywords "raster vector" and saw 52 threads on this topic.
i've used an outfit in ontario that scans old drawings and converts them to vector drawings... i've used it quite successfully for several hospital projects i've been involved with.
dik
we have used raster image in the past with mixed results.
for smaller renovations or additions it worked okay. problem
is, even if you get the scale worked out, the drawings are hand drawn and therefore errors will be evident.
the other problem is the speed. we found that raster images make the drawing regens sluggish.
if accuracy in dimensioning is not an issue, then you probably could use a raster image.
we have found the cost to vectorize an raster drawing image too high especially if you consider the possible inaccuracies that could be present. i prefer to have a junior draft the plan. at least any possibility of liabilities due to inaccurate drawings can be minimized.
thank you all for your comments. i have played around a bit with the file and i think i could make it work with enough time and effort. however, i have the same concerns as onteng... and they may win out in the end.
all of onteng's concerns are correct. but if you want to continue we use gtx rastercad with autocad successfully for what we want to accomplish.
mike