OCR reads text. It cannot read a P&ID. Identifying a control valve, a centrifugal pump, or a pressure transmitter from an engineering drawing requires computer vision — specifically a custom-trained object detection model. This guide trains YOLOv8 from scratch on P&ID symbols: dataset annotation strategy, ISA symbol taxonomy, high-resolution tiled inference, global NMS across overlapping tiles, spatial association with instrument tags, and production export to ONNX. Full working code for every s

Converting a scanned PDF to structured JSON is not a 10-line script — it's a six-stage pipeline. This guide builds it end-to-end in Python: PDF-to-image conversion at 300 DPI, OpenCV preprocessing, OCR with both Tesseract and AWS Textract, field extraction using regex patterns, table parsing, confidence scoring, and a production FastAPI endpoint with Pydantic validation. Full working code for every stage, Docker setup included.

Most OCR comparisons benchmark on invoices. This one doesn't. We tested AWS Textract, Google Document AI, and Azure Document Intelligence on what engineering teams actually need — high-resolution P&IDs, dense instrument tags, complex table structures, and legacy scans. One service lacks custom training entirely, one requires more setup than most teams can justify, and one consistently outperforms in production. Here's exactly what we found — with scores, code, and a clear recommendation.