OmniSch: A Multimodal PCB Schematic Benchmark For Structured Diagram Visual Reasoning

Recent large multimodal models (LMMs) have made rapid progress on visual grounding, document understanding, and diagram reasoning tasks. However, their ability to convert Printed Circuit Board (PCB) schematic diagrams into machine-readable, spatially weighted netlist graphs that capture component attributes, connectivity, and geometry remains largely underexplored, even though such graph representations are the backbone of practical electronic design automation (EDA) workflows. To bridge this gap, we introduce OmniSch, the first comprehensive benchmark designed to assess LMMs on schematic understanding and spatial netlist graph construction. OmniSch contains 1,854 real-world schematic diagrams and supports four tasks: (1) visual grounding for schematic entities, with 109.9K grounded instances aligning 423.4K diagram semantic labels to their visual regions; (2) diagram-to-graph reasoning, which requires understanding topological relationships among diagram elements; (3) geometric reasoning, constructing layout-dependent edge weights for each connection; and (4) tool-augmented agentic reasoning for visual search, which invokes external tools to accomplish (1) - (3). Our results reveal substantial gaps in current LMMs’ ability to interpret schematic engineering artifacts, including unreliable fine-grained grounding, brittle layout-to-graph parsing, inconsistent global connectivity reasoning, and inefficient visual exploration.