OCR for construction documents does not work, we fixed it
79 points - today at 4:05 PM
Source> OCR for construction documents does not work
I'm reminded of the Xerox JBIG2 bug back in ~2013, where certain scan settings could silently replace numbers inside documents, and bad construction-plans were one of the cases that led to it being discovered. [0]
It wasn't overt OCR per se, end-user users weren't intending to convert pixels to characters or vice-versa.
[0] https://www.youtube.com/watch?v=c0O6UXrOZJo&t=6m03s
hackcasual
today at 8:30 PM
JBIG2 does glyph binning, as you say not exactly OCR, but similar. So chunks of the image that look sufficiently similar get replaced with a reference to a single instance.
sreekanth850
today at 6:53 PM
We’re taking a different path, building a parsing engine that converts CAD (DWG/DXF) into fully structured JSON with preserved semantics (no ML in the critical path).We also have a separate GIS parser that extracts vector data (features, layers, geometries) independently,
Like to know how you handle consistency and reproducibility across runs using models and how you make it affordable, especially at scale. because as far as i know CAD and GIS need precision and accuracy.
interesting yeah parsing DWG/DXF natively makes sense when the source file is clean and well-structured. The precision argument is valid in controlled environments.
The challenge we kept running into is that construction drawings in the wild aren’t always that clean. Unresolved xrefs, exploded dynamic blocks, version incompatibilities, SHX font substitutions — by the time a PDF hits a GC’s desk it’s often the only reliable artifact left. The CAD source may not even be available.
That’s why we see vision becomes the more pragmatic path — not because it’s more precise than structured CAD parsing, but because PDFs are the actual lingua franca of construction. Every firm, every trade, every discipline hands off PDFs. So we made a bet on meeting the document where it actually lives.
On consistency and reproducibility — that’s a real challenge with vision models. Our approach is to keep detection scope narrow and validate confidence scores on every output rather than trying to generalize broadly. Happy to go deeper on that if useful.
oneneptune
today at 7:38 PM
Is this a service / product you plan to offer outwardly? I'd be interested in learning more. Use case: estimation.
I ran the example doors given and it missed 9 swinging doors, some that were in double swing pairs, and a few that were just out on their own not clustered. Not bad overall though
i18nagentai
today at 7:06 PM
OCR accuracy on technical documents is one of those problems that looks 95% solved until you hit the edge cases. Construction docs are especially tricky because of mixed handwriting, stamps, revision clouds, and poor scan quality. Curious how you handle multi-language documents — a lot of international construction projects have specs in two or three languages on the same page.
Looks cool! Where are you getting the data to finetune the cv models for element extraction? I'm worried there isn't a robust enough dataset to be able to build a detection model that will generalize to all of the slightly different standards each discipline (and each firm for that matter) use.
good q — we don't train on customer drawings. Our detection models are trained on a curated dataset of architectural drawings we've sourced and labeled ourselves, focused on the most common fixture and element types across CSI divisions.
The generalization problem you're pointing at is real and it's the hardest part of this. Our approach is to keep the detection scope tight — rather than trying to generalize across every firm's conventions, we train on a small but high-quality set of fixtures and optimize for precision within that scope.
The result is high confidence outputs on the elements we support, rather than mediocre coverage across everything.
We're expanding the detection surface incrementally as we validate accuracy division by division!
How in the world is an answer to a question from the account posting TFA replying directly to said question getting killed?
testUser1228
today at 5:37 PM
What do you foresee being the end use case for this (or most valuable use case)?
Anyone building in or for construction tech — whether that's a startup building estimating or project management software, a construction company with an internal tech team solving this themselves, or a builder looking to automate their workflow. The common thread is drawings. Every one of those groups lives and dies by their ability to extract actionable data from a PDF that was never designed to be machine-readable. We're building the layer that makes that possible so they don't have to start from scratch.
Why does the workflow lie at the level of a real or virtual piece of paper and not in the metadata from the applications used to create that piece of paper? Seems like a CAD tool would allow you to identify each element of the drawing, assigning metadata as required.
Only a small set of construction stakeholders participate in the CAD ecosystem (e.g., architects, large GCs) while a broader set of stakeholders (subcontractors, trades, smaller GCs/CMs) do not receive BIM files and work with PDFs. CAD/BIM is a wonderful aspiration but for many the reality is PDFs.
instig007
today at 6:55 PM
Re. "CAD/BIM", technically speaking CAD doesn't imply BIM, and the industry's promotion of BIM is akin to AI promotion among software engineering teams - the benefits aren't clear upon detailed review of the advertised capabilities. The CAD part, on the other hand, is generally recognized as the essential tooling for the profession and I'm surprised to hear that it just is a "wonderful aspiration".
cyanydeez
today at 6:12 PM
Oh you sweet summer child. These draws are anywhere from 0 to 120 years old and might just be something pulled out of a floppy disk from 1970 to scanned in coffee ridden pieces of paper sitting in a desk folded a hundred times.
The world in which metadata is a common thing attached to any file doesn't exist, and probably never will, no matter how much you try to improve CAD work flow.
When will this be available for 30000x8000px electrical diagrams?
I have to make a BOM and oh boy I hate my job
What software made the bitmap? Seems like a step earlier in the pipeline could help generate a BOM more easily.
I'm not really sure and I don't have access to it, I just recive flat PDFs or TIFFs
A lot of them are "archival" so I'm pretty OOL
You might even be SOL
It is telling that so many of the comments here assume the person with a thing that is not the most practical would be easily able to request thing in a different format. The assumption that the person with the inconvenient thing would never have thought to ask if more convenient thing was available and just willfully toiling with the inconvenient thing is kind of insulting.
oneneptune
today at 7:40 PM
Also, in the construction industry you get an updated drawing file a day before the bidding closes... good luck getting the GC to send more detailed files (that they themselves got elsewhere) in that time. You're better off sending it to your estimation department in India and letting them work through the night to put together the new estimations.
alexeischiopu
today at 5:30 PM
I’m building a similar platform, with electrical being furthest ahead - SLD, panels, lights, power, comms.
Also do doors, windows, and mechanical equipment.
dm, and I can include you in the next preview.
testUser1228
today at 6:55 PM
I'm not sure how to dm on here, but I'm very interested
You can paste "who is alexeischiopu" to a search engine, and since there isn't an athlete with the same name, a good candidate appears.
I work in the automotive field, I don't know if this complicates the things further but I appreciate any help!
What do you hate the most?
stronglikedan
today at 6:51 PM
silly questions
hspraggins77
today at 5:47 PM
Great points raised!
alexeischiopu
today at 5:30 PM
Good idea :)
cool. What's pricing like?
achillesheels
today at 4:57 PM
Love it! Starbucks Vente Machiato sip
Love to give it to an arc client, not sure who the right person to implement this would be? Hmm…
Of course it is not working. PDF and images are supposed to be tamper resistant. OCR tries to reverse engineer them.
kube-system
today at 5:01 PM
Since when is tamper resistance a part of PDF or any common image format?
PDF files can be signed, that is tamper resistance. Tamper resistance doesn't have to make any difference to the readability of the document.
kube-system
today at 5:23 PM
So can any type of file -- that doesn't have any relevance to the supposed design of every file type in existence. Now, later versions of PDF do have explicit support for signatures, but what does this have to do with preventing OCR? OCR reads a file, it doesn't change the original file.
True but you can make modified copies if you reverse engineer it with OCR.
ranger_danger
today at 5:40 PM
Some OCR solutions do change the original file, like OCRmyPDF. They take layers that were just images before and replace it with text layers so that you can search the document.
kube-system
today at 5:48 PM
That isn't OCR, but an application of the resulting output of OCR. Again, a signature on a PDF or any type of file doesn't prevent you from reading it. (It also doesn't technically prevent you from changing it, it just enables the detection of changes to a particular file.)
There's nothing about PDFs or image formats that prevent anyone from doing OCR. The reason construction documents are difficult to OCR is because OCR models are not well trained for them, and they're very technical documents where small details are significant. It doesn't have anything to do with the file format
ranger_danger
today at 5:38 PM
Can't one just remove the signature and re-sign it with anything else after tampering? Who verifies PDFs that hard?
kube-system
today at 5:55 PM
If you're performing OCR, you're almost by definition, disregarding the source file. The whole point of OCR is to be transformative.
You can't change a PDF, it is by design to be not easy to OCRed
kube-system
today at 6:50 PM
PDFs are merely an collection of objects, that can be plainly read by reading the file -- some of those are straight up plain text that doesn't even need to be OCR'd, it can be simply extracted. It is also possible to embed image objects in PDFs, (this is common for scanned files) which might be what you are thinking of. But this is not a design feature of PDF, but rather the output format of a scanner: an image. Editing PDFs is a simple matter of simply editing a file, which you can do plainly as you would any other.
ware-intel
today at 6:04 PM
Your smart features looks like a game changer? Nice job!