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 work

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.