As-built trench survey with PIX4D & the Topcon CR-H1

Water is one of the earth’s most essential resources, and managing it goes far beyond supply; it requires the safe collection and disposal of wastewater through increasingly complex treatment processes. As global demands grow, continuous investment and technological advances are needed.

We spoke with Tomasz Witkowski, Regional Sales Manager at TPI, a leading surveying solutions company, about how to scan and generate an accurate CAD-ready 3D model in minutes for long-term asset tracking.

The limits of a traditional as-built trench survey

Traditional as-built trench surveys rely on single-point data collection using total stations or GNSS receivers. Despite their accuracy, these conventional methods take time, require physical access in potentially hazardous excavations, and record isolated points.

TPI uses the reality capture smartphone app PIX4Dcatch with the Topcon CR-H1 RTK device to overcome these challenges. They use the data in PIX4Dmatic for processing, generating a complete and measurable 3D environment.

TPI uses reality capture app PIX4Dcatch backed by high-precision RTK GNSS positioning, the Topcon CR-H1. Instead of recording isolated points, the field team captures the scene using PIX4Dcatch. They then use PIX4Dmatic then processes to automatically generate a complete, measurable 3D environment.

Water and wastewater utility mapping

To illustrate how mobile scanning with PIX4Dcatch and the Topcon CR-H1 optimizes as-built surveys, Tomasz walks us through one of the most demanding fieldwork tasks: mapping underground water and wastewater infrastructure before backfilling.

An open trench exposing a complex network junction (valves, flanged tees, couplings, or pipes crossing at various angles) is a daily reality for utility surveyors. Access to these trenches is often strictly time-limited. Green cameras indicate the trajectory in the dataset visualizer.

In this case study, the surveyor had only a brief window to capture data. A standard point-based survey would have taken several times longer and failed to capture the true spatial alignment and physical dimensions of the fittings.

How to speed up trench documentation with PIX4Dcatch and and RTK device

To execute high-speed, centimeter-accurate trench documentation, TPI used a set up of integrated smartphone scanning with RTK positioning, combined with desktop processing.

• Data collection: PIX4Dcatch for data capture, coupled with the Topcon CR-H1 system for accuracy.
• Processing: PIX4Dmatic is optimized for efficient processing and fast field-to-CAD processing.

Workflow: documenting a trench with a mobile device

1. Data collection with smartphone: instead of single-point measurements, the operator simply walked along the trench with a smartphone, viewing the live trajectory in the app.
2. Optimal geometry: walking around the utility network from accessible angles (including under exposed pipes) ensured complete geometry coverage without entering hazardous zones.

3D mapping of exposed pipes from accessible angles outside the trench. Green markers show the capture path

4. Control & spatial accuracy: three ground control points (GCPs) measured with the Topcon CR-H1 receiver ensured exact orientation in the project's coordinate reference system.
5. Processing in PIX4Dmatic:data was imported into PIX4Dmatic via simple drag-and-drop to generate a dense, geometrically accurate 3D point cloud and textured mesh*. The software automatically identified and isolated specific features, terrain breaks, clear pipe outlines, and fine fitting details from the 3D data.

*Note: PIX4Dcatch and PIX4Dmatic also support Gaussian splatting, enabling measurable and georeferenced hyper-realistic results while enhancing overall quality of other outputs

Marking the characteristic points of water and sewage fittings

Results & key benefits

TPI achieved significant efficiency gains over traditional methods:

• Substantial time savings: field scanning that previously took hours with a total station was completed in minutes. Office computation in PIX4Dmatic cut processing time nearly in half compared to standard photogrammetry tools.
• Zero omitted data: rather than storing isolated coordinate points, the entire trench is saved to digital memory. Missing details (such as pipe diameters or coupling slopes) can be extracted from the point cloud at any time.

The workflow enables taking high-precision distance measurements from a safe distance

• In-software vectorization: using PIX4Dmatic’s built-in tools, the team calculated trench surface areas, vectorized linear utility elements, and marked key structural points directly on fittings. The data can be exported to standard CAD/GIS formats.

Vectorizing utility elements and pipe centerlines directly inside PIX4Dmatic

• Enhanced field safety: High-precision data capture was completed entirely from the edge of the excavation, removing the need for field personnel to step into unsafe trenches.

Calculation of the excavation area

From site documentation to long-term digital assets

Post-construction and emergency repair surveys are often impossible to repeat once buried. What used to be a static photo record or a sparse set of survey points is now a fully measurable 3D model ready for instant CAD drawing and long-term asset tracking. Replacing slow, traditional methods with reality capture can meet the growing global demand and ensure that the cost invested in vital water and wastewater infrastructure is backed by an accurate, digital record.