Subsea photogrammetry

Understand subsea photogrammetry

Subsea photogrammetry leverages geometric measurements derived from multiple 2D images, captured from various viewpoints, to recreate precise 3D models of structures or areas. At IVM Technologies, all our Hydro Series cameras are equipped with dual cameras that capture 4 frames per second, while the surface unit software allows you to visualize 20 frames per second. The data is transmitted via a tether from the camera to a computer and, after the inspection, this data is processed by a software that transforms it into a 3D model, true to real dimensions of the inspected asset.

Step 1: Data acquisition

Every survey starts with an ROV fitted with a Hydro Series unit, capturing high-overlap images of the target structure. Since visibility directly impacts success, we’ve integrated an advanced lighting system to ensure uniform image quality under all conditions.

A structured coverage plan is critical: the ROV follows a pre-defined path tailored to the asset’s geometry. For flat surfaces (e.g., pipeline spans), parallel passes work best. For complex structures (like manifolds or jacket legs) we combine circular orbits and linear transects to eliminate blind spots and guarantee full coverage.

Step 2: Image processing

Once the images are collected, advanced software identifies common points across the photographs. This creates a sparse point cloud, which serves as the foundation for the model.

Step 3: 3D reconstruction

The sparse point cloud is then densified into a detailed mesh, where every surface feature is preserved with sub-millimeter precision. The result is a digital twin of the asset, which can be: measured for dimensional control, compared against CAD designs or previous inspections to detect changes over time, and annotated to highlight defects, such as cracks, marine growth, or structural deformations.

Step 4: Analysis & delivery

The final 3D model is more than just a visual tool, it’s a powerful analytical resource. Deliverables are tailored to each project, whether it’s a simple visual inspection or a comprehensive structural integrity assessment.

What does calibration involve?

At IVM Technologies, each underwater photogrammetry unit is pre-calibrated in a controlled tank environment, using a 3D calibration device that features 71 high-precision targets. The process includes capturing multiple images of the device from different angles to:

• calculate lens distortion
• define the relative geometry between the two cameras
• scale the system using known distances

From that, a unique calibration file is generated and linked to the device’s serial number. Both the calibration device and its associated file are provided with each unit, ensuring you have everything needed to import accurate parameters into your processing software.

Underwater photogrammetry offers a unique combination of accuracy, cost-efficiency, and visual clarity that conventional inspection methods like video recording or sonar often can’t match. Beyond creating beautiful 3D renderings, photogrammetry enables highly accurate models that offer quantifiable data for critical metrology. Unlike conventional video, which is limited by low resolution, poor visibility, and motion blur, it generates fully usable 3D models with true texture, allowing for precise measurements and analysis. It is also a time-saving solution, significantly reducing operational time and costs of subsea asset inspections: spool metrology surveys, for instance, can be reduced by up to seven times compared to methods using expensive acoustic spreads.

As a fully independent, non-contact measurement tool, the Hydro Series cameras require no additional sensors, ladders, or asset markers, enabling 100% free-flight inspections without reference points or navigation aids. Compared to sonar or acoustic methods, underwater photogrammetry delivers the millimetric accuracy needed for detailed dimensional control and integrity analysis. Digital stills used in our subsea photogrammetry units also outperform conventional video in terms of resolution, exposure control, and measurement accuracy.