curvy slabs

[Anonymous]

Hello,

assume you have a 40 years old archive of about 500 hand made projects. As they are both valuable and profitable, you want to convert them into a digital archive. About 4/5 of the drawings consist of projections that can be calculated on the fly by a BIM CAD, so the problem reduces to importing the 2d plots. You take someone in your staff and ask him to do this accurately. He takes an old project, make a tiff image out of it, then read the image with the CAD and... now what? The person comes back to you with a pesky problem: the slabs are curvy, hand drawn, and the conversion turns out to be really difficult and less than accurate. You are not allowed to change the original shapes: the digital version must be an accurate 1:1 import of the original. I recollect the similar problem occurring in the 80', when the CAD could only draw straight lines and we had to give up with the very idea of using a CAD. Twenty+ years later, the situation has improved, so much that you can draw a curvy slab directly on the CAD, but the problem is still pending when importing old projects. There is indeed a difference between drawing directly in CAD and importing from an old project, and the 1:1 conversion is a must. The conversion of hundreds of project makes the case for a rapid method. Then my question is, how would you solve this problem with AC10?

[Thomas Holm]

There is special software available to convert and vectorize scanned drawings. I wouldn't buy it, I'd buy that service from a service bureau instead, especially if it's a big one-time job. (I hear they're cheap in India).

But if you plan to go on working on an existing building, I'd still advice you not to vectorize, just import the raw scans into Archicad as background images, and then re-draw over them with Archicad's tools, all the time checking against dimensions obtained from on-site measurements.

The thing is you need human intellgence and architect's knowledge to interprete the scanned lines: What are walls, windows, etc, And if you want to re-use this info in Archicad, you need to be in the correct format, drawn with the correct tool.

Besides, there is no such thing as a 1:1 exact drawing. It was once interpreted and built. Unless this is a pure drawing archive, what you are really interested in is the existing building.

[Anonymous]

The projects have been kept up-to-date, and the dimensions are highly accurate, thank goodness. 🙂

What I have in mind is a magic wand that translates any line under the cursor as "part of" the slab, it then draws the edge of the slab until it finds a junction, then wait for my input, and so forth. In this way, selected lines in the background tiff image are automatically converted, with no need to make any guess work. This would be the ideal solution...

I agree against vectorization. We tried two different programs, but they were not good enough. We are still looking for a high quality vectorizer, but I think the above magic-wand would be a better solution.

[Thomas Holm]

jdk wrote:
...a magic wand that translates any line under the cursor as "part of" the slab, it then draws the edge of the slab...

That works already, more or less, IF the line is a vector (line or polyline or curve).

But not if it's just a chain of dots from a scanner. If that would work, it would be nice, but still it would be vectorizing! If you're familiar with Archicad, I think you could draft using Archicad tools and pet-palette tweaks faster, or at least with much better precision, than the tool you describe, if you include all the time needed to correct errors.

The problem lies in the difference between CAD precision and hand drafting scanned. No matter how good the original drawings, the paper copies scanned, the scanner and the software is, you will get a result with more errors to correct than acceptable for BIM work!

[Anonymous]

> you will get a result with more errors to correct than acceptable for BIM work!

Thomas, are you referring to the type of errors that one observes when passing the drawing through a vectorizer? Although a magic wand could be affected by the similar problem, it could be easier to manage, as it would be limited to one segment at the time, the one under the cursor, instead of making guess work with all the imperfections of an old technical drawing. Further, as my concern is about curves, vectorizers deal with them via a chain of knots instead of a proper curve; the magic wand would use a proper curve between two points. As I have never had the pleasure to see one such tool in 20+ years, mine is an informed wish... 😉

If you are referring to distances, I am lucky enough to have a very good scanner that returns trouble free images on this respect.

.... Just in case, what is the very best vectoriser to date?

Bob

[Anonymous]

Thomas wrote:
No matter how good the original drawings, the paper copies scanned, the scanner and the software is, you will get a result with more errors to correct than acceptable for BIM work!

Even worse...

The better the originals...the smaller the errors...the greater the nightmare of repairing the model.

It is MUCH harder to fix errors of 64ths of an inch, hundredths of a degree and parts of a millimeter than to simply draw things right from scratch.

[Anonymous]

jdk wrote:
Although a magic wand could be affected by the similar problem, it could be easier to manage, as it would be limited to one segment at the time, the one under the cursor, instead of making guess work with all the imperfections of an old technical drawing.

What advantage do you see to this as opposed to accurately tracing the drawing using the tools we already have?

Numeric input is now so direct and easy in AC10 that using the scan as a guide and entering the correct values as you go seems easier to me than getting close with a magic wand to raster approximation followed by tweaking and adjusting.

[Dwight]

The way I do it is after assessing the drawing for inherant repeatable modules, I have a helper call out the dimensions as we work around the structure in a clockwise direction. The wall is applied first using the segment wall method. Then the helper only calls the displacement from the last node:

x, 1
y, 1
etc.

This CAN be done overlaying the plan scan, but it is quicker to do it from scratch as far as possible and only then make the scan visible.

Windows and other elements are added later according to dimension, not graphics, because Archicad can supply so much more data than the plan view can. At this point, assessing geometry repeats is important because once windows in one repeat unit are placed, the efficiency of copying grows.

This method seems archaic because it denys the graphic input of the existing plan but is really fast and completely ignores the flaws in scanning technology and printer stretch - Once the basics are located dimensionally, the graphic flaws in the underlay reveal themselves.

[Anonymous]

Looking around, right now, I bumped into these two programs:

http://www.adobe.com/products/illustrator/pdfs/creating_vector_content.pdf
http://www.silhouetteonline.com/

Both seem to make a very nice job, so it looks possible to make a good vectorization. I shall give them a go.

>Numeric input is now so direct and easy in AC10 that using the scan as a guide and entering the correct values as you go seems easier to me than getting close with a magic wand to raster approximation followed by tweaking and adjusting.

I am not an AC10 wizard, yet. Could you be more specific?

[Dwight]

A scanned plan is always going to dither and anti-alias drafted lines - If you have a 24x36" scan, that scan will probably not exceed 100 dpi.
Also the printed lines are FAT.
Actually picking the center of a line is tricky. Combined with the crooked fuzziness of antialiasing, graphically, you are alway 3 to 6" out of true on a 1/8" scale plan.

For accurate tracing you need absolute hairlines - no print on paper scanned can do this.