topic Re: curvy slabs in Modeling

curvy slabs

Anonymous — Thu, 25 May 2023 15:58:26 GMT

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?

Re: curvy slabs

Thomas Holm — Tue, 10 Oct 2006 10:16:55 GMT

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.

Re: curvy slabs

Anonymous — Tue, 10 Oct 2006 13:52:43 GMT

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.

Re: curvy slabs

Thomas Holm — Tue, 10 Oct 2006 15:57:11 GMT

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!

Re: curvy slabs

Anonymous — Tue, 10 Oct 2006 16:29:51 GMT

> 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

Re: curvy slabs

Anonymous — Tue, 10 Oct 2006 16:34:25 GMT

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.

Re: curvy slabs

Anonymous — Tue, 10 Oct 2006 16:40:06 GMT

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.

Re: curvy slabs

Dwight — Tue, 10 Oct 2006 17:08:39 GMT

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.

Re: curvy slabs

Anonymous — Tue, 10 Oct 2006 17:09:27 GMT

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?

Re: curvy slabs

Dwight — Tue, 10 Oct 2006 17:14:10 GMT

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.

Re: curvy slabs

Dwight — Tue, 10 Oct 2006 17:17:07 GMT

Vector scan programs only define contrast edges, not drawing intent. Printing induces ambiguities that these applications cannot overcome to the detail architects need.

Re: curvy slabs

Anonymous — Tue, 10 Oct 2006 17:37:00 GMT

Mhhh... looks like we should give up with the very idea of automatic 1:1 vectorization for CAD.

I looked at SketchUP again, which is so easy with straight lines and regular half circles. But when it comes to free curves, I have trouble in matching vectors with the underlying raster. My own eyes are in pain (-6 of myopia).

Re: curvy slabs

Dwight — Tue, 10 Oct 2006 18:06:11 GMT

Some things that should be automatic, aren't.

It always depends on your standards. How close do you need to be?

I figure you'd need to scan a 6x0 rapidograph on mylar film at 300 dpi to get an acceptable auto-trace, but even then, inadvertent stretching of the film and imperfect placement will mean the scanlines will occasionally misalign one or more pixels for a crooked interpolation.

Man-yule is best.

Re: curvy slabs

Thomas Holm — Tue, 10 Oct 2006 21:30:42 GMT

Seems like my masters are chiming in to save my skin....

Bob. The truth is, you will never get an accurate model from the process you describe. If you're ready to accept errors, then OK. But small errors tend to add up, or worse, multiply.

In addition to what my colleagues say, I'd like to add the obvious fact that a line drawing is a symbol. When we draft manually, we utilize this fact. Things are supposed to look good and clear, and roughly to dimensions given. But we also state (usually in the drawing's description) that when dimensions are given as numbers, they count. Dimensions taken by measuring the drawing with a ruler are not valid. There's a reason for that!

Also, I've used Illustrator's vectorizing, I just say good luck! It will even save as dwg which you can import into Archicad lines, not just as an uneditable pdf. It is very good. For logos.

But not good enough for this purpose. If you want vectorizing as good as it gets, you will need a specialist - a service bureau. Take Matthew's and Dwights advice! Also, get some professional Archicad training! Money spent on that will pay for itself, many times over what you spend on useless vectorizing!

Re: curvy slabs

Dwight — Tue, 10 Oct 2006 21:33:58 GMT

The parallel is renovating an old house. At some point you make new over what is a crooked original. Twenty coats of paint and the dimensions aren't real anymore.

Re: curvy slabs

Anonymous — Wed, 11 Oct 2006 08:57:33 GMT

>Also, get some professional Archicad training!

This is past the deadline, as we are near the decision of Archicad vs Revit, stepping away from AutoCAD. But the specific problem of automatic vectorization from a printed project has nothing to do with an individual's expertise in using the tool named ArchiCAD. I disagree with the very claim that automatic vectorization is necessarily bad. It just happens that the present vectorizers are less than perfect, just like OCRs are, but some are better than others, and technical research is making progress, just like it did with stone-age AutoCAD vs ArchiCAD's BIM. I am free from the dogma that things must stay as they are at this time. I understand that the main argument against proper vectorization is, that it would take work away from human professionals. I just belong to a different school.

Bob

Re: curvy slabs

Thomas Holm — Wed, 11 Oct 2006 10:55:25 GMT

jdk wrote:
I understand that the main argument against proper vectorization is, that it would take work away from human professionals.

Bob,

I'm sorry, but if THAT is what you've read in our posts, then you've understood nothing!

Even if I'm old, I've used CAD since it was new, and have had - and still have - high hopes for automation. I've used vectorization too. It's fine for what it does, but it simply doesn't give you a good base for BIM models, when what it does is interprete manual, copied and scanned drawings And the reasons for this are inherent in the process.

It's not the vectorization per se. We're telling you that today it is faster to use a trained person to input the data, than to use that same person to correct erroneous input from a program.

My conclusion might be different if you were speaking about using data from on-site point cloud laser measurements. But you are not.

If you don't want to listen, you've got a problem. Not our problem though. Take off those pink glasses!

Re: curvy slabs

Anonymous — Wed, 11 Oct 2006 13:30:38 GMT

jdk wrote:
I disagree with the very claim that automatic vectorization is necessarily bad. It just happens that the present vectorizers are less than perfect, just like OCRs are, but some are better than others, and technical research is making progress

Bob,

You are talking to some of the most advanced, technology friendly people anywhere. We all got into this to find ways to automate the drudge work so that we can spend more time improving the quality of the work (design). We are also realistic about what is possible.

My physics professor once pointed out that if you have paced off the diameter of a circle you can't get a more accurate value for the circumference by adding decimal places to your value for pi.

As far as vectorization goes it is fundamentally limited by the quality of the information going in (the GIGO principle in computer science). Line work on paper (or ink on mylar) simply isn't accurate enough to produce a proper base for a building model. Now it may be that someday computers will actually be able to read drawings, but I wouldn't hold my breath waiting for this development. Especially considering that most of our highly educated clients don't understand architectural drawings either.

I can imagine two developments that might improve the situation.

1. BIM software could become more accommodating of errors and discrepancies. This was sort of true with integer based CAD since the field of available points was more limited. In the floating point world it would require some built in way to keep things tidy within some defined margin of error and prevent small errors accumulating or showing up as gross anomalies. This could be an advance if well implemented, but any time the software makes assumptions and automatic adjustments I get worried about how well the programmers have anticipated my needs.

2. Vectorization with interpretation. This would require some advanced heuristics to rectify nearly right angles, normalize small fractions, and so on. This would be similar to adding a spell checker to OCR to improve accuracy, only much more complex.

The comparison to OCR is probably apt if you also consider that vectorization is a much more complex task. Considering that OCR has a vastly larger market and is still not entirely worked out I think we can expect to wait a very long time before we see any acceptable results in this area for our little corner of the marketplace.

There are some things that computers just aren't very good at and recognizing complex patterns of information represented graphically is one of them. There are some ways that John Henry still beats the steam drill.

Re: curvy slabs

Anonymous — Wed, 11 Oct 2006 14:11:26 GMT

I enjoyed the discussion, and I thank you for it. We still have the problem of how to vectorize cury slabs, by hand or otherwise. The type of curves we have are difficult to replicate, firstly because they were hand drawn without any geometrical reference, such as foucs points for ellipses. The 1:1 replication of these curves is a challenge. Perhaps the most rapid solution is to use a very-high resolution tablet, with a digital pen, and go over the lines by hand.

>I've used vectorization too. It's fine for what it does, but it simply doesn't give you a good base for BIM models, when what it does is interprete manual, copied and scanned drawings And the reasons for this are inherent in the process.

As I go along with most of what I've red in the messages, I conclude that we misunderstood each other. I was not wishing for a magic tool that builds and ArchiCAD model out of a printed project; it would be wonderful to have, but is clearly not around at this time. It is clear that one has to rebuild the model by hand, and I cannot recollect anything I've said that might have triggered the doubt. What I have said is, that a magic wand (similar to the one that already exists in ArchiCAD) could help in the process of vectorizing curvy slabs. Another idea is to use interpolating points with concavities, instead of re-tracing the curves by hand, which process is error prone. I've seen many CAD designs, but none of them had this problem. CAD is good for straight lines and regular curves, but the sort of curves we have are a challenge.

Re: curvy slabs

Anonymous — Wed, 11 Oct 2006 14:18:56 GMT

jdk wrote:
I enjoyed the discussion, and I thank you for it. We still have the problem of how to vectorize cury slabs, by hand or otherwise. The type of curves we have are difficult to replicate, firstly because they were hand drawn without any geometrical reference, such as foucs points for ellipses. The 1:1 replication of these curves is a challenge. Perhaps the most rapid solution is to use a very-high resolution tablet, with a digital pen, and go over the lines by hand.

For tracing freehand curves I use the spline tool. It is very easy to use with a minimum of control points. If your curves do not have a strict defining geometry then close enough probably is. You can then magic wand to the spline to approximate the curve with arcs for the model elements (they don't like splines).