56th Street Underpass – SLAM and Aerial Combined
Oct 02, 2024
Combining airborne LiDAR and colorized SLAM scanning can deliver unmatched detail for complex infrastructure projects. The 56th Street Underpass survey in Denver, CO is a perfect example—capturing both the above-ground roadway and the below-grade pedestrian pathway in one cohesive dataset.
Mission Overview
- Platform: DJI Matrice 300 RTK
- Sensor: ROCK R3 Pro V2 (32-channel variant)
- Flight Altitude: ~50 m AGL
- Flight Speed: 5 m/s
- Ground Scanning: ROCK R3 Pro V2 with SLAM Dock V2
- Deliverables: High-accuracy aerial LiDAR dataset, colorized SLAM point cloud of underpass, integrated dataset
This project demonstrates the R3 Pro V2’s unique ability to seamlessly combine aerial mapping and GNSS-denied scanning—all within the same workflow.
Project Location
The survey area is located near the intersection of 56th Ave and Dallas Street in Denver, Colorado.
Boundaries:
- North: 58th Ave
- West: Chester Way
- East: Dallas Street
- South: Area extending beyond 56th Ave to capture the entire underpass in the airborne survey
Additional coverage included the Northfield Tennis Courts, which served as an optimal location for camera calibration.
Why This Site?
The 56th Ave Underpass is a mixed-environment mapping challenge:
- Above-ground: 56th Ave roadway and surrounding infrastructure require high-altitude aerial LiDAR capture for context and integration into larger corridor datasets.
- Below-ground: The pedestrian underpass sits in a GNSS-denied environment, making SLAM the only practical scanning method.
- Seamless Integration: Merging aerial and SLAM datasets ensures a continuous, accurate, and visually rich point cloud from road surface to underpass interior.
Data Acquisition
Aerial Mission
The DJI M300 equipped with the R3 Pro V2 flew at 50 m AGL and 5 m/s, optimized for:
- High point density from the XT32 LiDAR sensor
- Dual returns for capturing both surface details and low vegetation
- RGB imagery for colorizing the point cloud and orthophoto generation
SLAM Mission
Using the SLAM Dock V2, the R3 Pro V2 was carried through the underpass to:
- Capture accurate geometry without GNSS
- Produce a colorized interior point cloud with 360° imagery
- Ensure alignment to aerial data through ground control tie-ins
Processing Workflow
Both datasets—airborne and SLAM—were processed through ROCK Cloud:
- PPK Trajectory Processing for aerial data to achieve 2–3 cm absolute accuracy.
- SLAM Alignment to merge the underpass interior seamlessly with the aerial point cloud.
- Colorization using RGB data from both aerial and SLAM missions.
- Final Integrated Deliverable ready for engineering and inspection workflows.
Results
1. Integrated Point Cloud
A single dataset containing both aerial and SLAM data offers a continuous 3D model of the roadway and underpass, eliminating data gaps.
2. High-Resolution Orthophoto
The aerial capture produced a crisp, survey-accurate orthophoto for planimetric mapping and visual analysis.
3. Colorized SLAM Interior
The underpass interior dataset, captured with the SLAM Dock V2, is fully colorized—ideal for inspection, clearance measurement, and asset documentation.
Applications for the Dataset
This combined dataset can be used for:
- Infrastructure Inspection
- Roadway & Pedestrian Pathway Design
- As-Built Documentation
- Clearance and Safety Analysis
- Urban Planning
Key Takeaways
- The R3 Pro V2’s dual capability for aerial and SLAM missions streamlines complex projects with multiple scanning environments.
- Combining 50 m AGL aerial LiDAR with SLAM interior mapping creates a dataset that would otherwise require multiple systems.
- ROCK Cloud’s integrated processing makes merging, colorizing, and delivering multi-source datasets simple and efficient.