SLAM Scan Path Planning Guide: Better Handheld LiDAR Mapping

Direct Answer

Scan path planning is the key to obtaining high-quality SLAM mapping results. Core principles: ① Initialize in feature-rich areas; ② Maintain a stable walking speed (0.5–1.0 m/s); ③ Create loop closures whenever possible (every 100–200 m); ④ Use a "small loop within a large loop" room-by-room strategy for indoor spaces; ⑤ Scan large scenes by zones, keeping single sessions under 30 minutes; ⑥ Slow down during scene transitions and keep both scenes visible simultaneously; ⑦ In special environments (epoxy floors, glass curtain walls, long straight corridors), adjust scanning angles or place reference objects with distinct features.

Why Is Scan Path Planning So Important?

The SLAM (Simultaneous Localization and Mapping) algorithm continuously matches environmental features to calculate the device position and build a map. When the scan path is properly designed, the system can:

Obtain more environmental features
Improve trajectory matching stability
Reduce accumulated errors
Increase loop closure detection success rate
Improve overall point cloud accuracy

If the path planning is poor, the following issues may occur:

Point cloud drift
Wall misalignment
Floor tilting
Local ghosting
Mapping deformation
Point cloud layering

How Should the Route Be Planned Before Scanning?

It is recommended to observe the site environment before starting the scan.

1. Plan the Complete Route

Familiarize yourself with the scanning environment and plan the route in advance — avoid changing the route during scanning
Open doors that need to be entered in advance
Turn on indoor lighting
Remove obvious obstacles
Minimize pedestrian movement and object movement

2. Check Device Status

Ensure sufficient battery power and storage space
Check whether the camera lenses and LiDAR are clean

Initialization Guidelines

Select a feature-rich location for initialization. Place the scanner at a certain height on a level surface. Initialization priority: tabletop > floor.
Orient the device toward the target object whenever possible, such as a tunnel entrance, soil pile, or building facade.
Do not initialize in open areas with insufficient features, such as plazas or grasslands.
Avoid initializing too close to a wall (less than 1 meter), which may result in insufficient environmental features due to a limited field of view.
Avoid areas with many dynamic targets, such as intersections, crowded pedestrian areas, or water surfaces. If there is abundant vegetation, initialize under calm or light-wind conditions.
Avoid initializing in highly reflective environments, such as mirrored walls, bathrooms, glass curtain walls, epoxy-coated garages, or large metallic reflective areas.

Path Planning Strategies

1. Plan the Scanning Route in Advance

Avoid frequent backtracking or irregular movement. Keep the route smooth and continuous.

2. Create More Loop Closures

① Start-End Loop Closure

At the end of the scan, if the start point and end point form a loop, accumulated errors can be effectively reduced. It is recommended to form an "O"-shaped loop instead of returning along the same path. The overlap trajectory should be maintained at 5–20 m. For long continuous scans, create a loop every 100–200 m.

② Intermediate Loop Closure

During scanning, intentionally revisit previously scanned areas to create an "8"-shaped loop. Each loop closure provides an opportunity to reduce accumulated errors.

③ Indoor Spaces — Scan Room by Room

Use a "small loop within a large loop" strategy:

Each room forms a local loop
Each floor forms a global loop
For complex spaces, scan one loop clockwise and one loop counterclockwise to reduce blind spots and occlusions
After finishing a room, return to the doorway or corridor before entering the next room

3. Large Scenes — Collect by Zones

For large residences, villas, or office buildings, long continuous scans are not recommended. Data can be collected by floor, functional area, or room, and then merged afterward to reduce layering risks.

Recommended maximum duration:

Point cloud acquisition: within 30 minutes per task
Gaussian Splatting (3DGS): within 10 minutes per task

Scene Transition Techniques

When transitioning between different environments, the scanner must re-establish feature matching between the two scenes.

1. Room Transition

When two rooms are connected by a narrow doorway, slowly enter sideways while holding the device close to your chest. Keep both rooms visible for several seconds until the system establishes feature correspondence before fully entering. Avoid scanning a door while it is being opened — enter after slowly opening the door while standing behind it.

2. Corridor Turns

Slow down at corridor corners, especially in narrow corridors. Use a larger turning radius and keep the scanner facing the inner corner wall.

3. Stair Turns

Keep the LiDAR facing the inner handrail and avoid blocking the LiDAR with your body. Avoid rapid rotation in place.

4. Staircase Scenes

When scanning stairs from bottom to top, the downward blind zone of the LiDAR may cause incomplete capture of stair treads and risers. It is recommended to scan from lower floors to higher floors and from bottom to top.

Special Environment Considerations

① Epoxy-Coated Parking Garages

The high reflectivity of epoxy floors may enlarge LiDAR spot size and cause Z-axis drift. In such environments, slightly tilt the scanner upward to reduce the influence of ground points.

② Glass Curtain Walls and Highly Reflective Scenes

Highly reflective scenes such as glass curtain walls, mirrors, and dance studio mirrors can reflect or transmit laser light, easily leading to missing point clouds, increased noise, or abnormal mapping. It is not recommended to use these environments as the primary scanning area. If necessary, adjust the scanning angle and add other features to assist in data acquisition.

③ High-Rise Buildings and Obstructed Scenes (RTK)

When using RTK, choose environments with open skies and avoid tall buildings, trees, etc., that obstruct satellite signals to ensure effective RTK positioning.

④ Repetitive Texture Scenes

Scenes with many repetitive structures, such as long straight corridors, tunnels, and underground utility tunnels, are prone to trajectory drift or layered resolution due to similar environmental features. It is recommended to place reference objects with distinct features approximately every 50 meters and combine this with loop-back scanning to improve mapping stability.

⑤ High-Noise Scenes

In dusty construction sites, recently blasted mines, rainy or snowy weather, or environments with a large amount of floating particulate matter, laser echoes are easily interfered with, leading to increased point cloud noise and decreased data quality. It is recommended to avoid scanning in such environments, or to wait until the environment stabilizes before commencing operations.

Best Practices During Scanning

1. Maintain a Stable Movement Speed

Recommended speed:

General indoor and outdoor environments: 0.5–1.0 m/s
Narrow spaces (corridors, tunnels, stairs, etc.): ≤ 0.5 m/s

Avoid: running, frequent stopping, sudden acceleration or deceleration, sharp turns or sudden turnarounds.

2. Maintain Device Stability

Keep the device stable and avoid excessive shaking or rapid swinging. Maintain a natural and stable walking posture, slow down when turning, and avoid large device swings.

3. Monitor Scan Coverage in Real Time

Check the real-time point cloud preview in the App regularly. Pay special attention to: room corners, doorway areas, wall corners, stair areas, around large equipment, under furniture or equipment.

4. Adjust Scanning Angles Flexibly

For areas prone to occlusion — corners, tight turns, under equipment, under furniture — adjust device height or scanning angle as needed.

5. Multi-Angle Coverage of Key Areas

In complex spaces, use a combination of forward and reverse scanning to improve completeness and reduce blind spots.

6. Reduce Dynamic Object Interference

Avoid frequent pedestrian traffic, moving vehicles, doors or windows opening and closing continuously, and large-scale vegetation movement. If dynamic objects cannot be avoided, reduce movement speed and increase loop closures.

SHARE3DCAM Scanning Recommendations

✓ Start scanning in feature-rich areas
✓ Maintain a stable speed (approximately 0.5–1.0 m/s)
✓ Create multiple loop closures whenever possible
✓ Cover important areas from multiple angles
✓ Scan multi-story buildings floor by floor
✓ Check point cloud completeness before leaving the site

These practices can significantly reduce drift and achieve more stable and complete SLAM mapping results.

Conclusion

For handheld SLAM LiDAR scanning, scan path planning is often just as important as the device itself. Proper path planning, effective loop closure design, and sufficient multi-angle coverage can significantly improve point cloud quality and reduce post-processing effort. Taking a few minutes to observe the environment and plan your scan strategy before each project will save significant time in downstream data processing and application.