CrackRuler

Photograph a concrete crack next to a printed marker. Get its width in millimetres and a clear next step.

Inspection inputs

1 Photo

or try a sample

    2 Exposure

    Sets the width the crack is compared with. Values from ACI 224R-01, Table 4.1.

    3 Marker

    Print the marker at 100 %, measure the black square with a ruler and enter what you measured.

    Choose a photo or a sample.

    Results

    What you get

    1. Width in millimetresalong the whole crack, from a printed ArUco marker that fixes scale and removes camera tilt
    2. A comparator readingeach crack plotted against the guideline width for its exposure
    3. A next steplog, monitor, engineer review, or retake, with the reason
    4. The agent's traceevery OpenCV tool it ran, what it saw and why it chose the next one

    Comparator

    Reference lines are drawn at their relative thickness. The notch is the guideline for the exposure you picked.

    How it works

    1. Quality gatesharpness and exposure of the frame; a blurred frame ends in a retake request.
    2. Scale and planeOpenCV 5 aruco.ArucoDetector finds the marker with sub-pixel corners; a homography makes the surface fronto-parallel at the marker's native pixel density. The marker edge doubles as a blur probe (10–90 % edge rise gives the optical sigma).
    3. Finda small U-Net (1.56 M parameters, ONNX) runs in the OpenCV 5 DNN engine on a 1024 px view; a classical multi-scale Hessian ridge detector runs as an independent second opinion.
    4. Measureon the full-resolution rectified image: centreline by thinning, grey-level profiles across the crack every few pixels with cv.remap, full width at half depth, then a blur model inverts the optics. Widths the optics cannot resolve are reported as upper bounds.
    5. Decidethe widest confirmed crack (95th percentile along its length) against the ACI 224R-01 guideline for the chosen exposure, with uncertainty. Too close to call, unconfirmed, or unresolvable cases go to a person.

    ACI 224R-01 Table 4.1 is a design guideline for new construction under service loads. ACI notes that a portion of cracks will exceed it. CrackRuler uses it to route a finding, never to certify a structure as safe. Photos you upload are processed in memory and are not stored; only the report and the annotated image are kept for 7 days.