Merge scans in Aura

This article explains how to merge multiple Aura scans into a single, seamless point cloud using the Merge workflow.

Aura's Merge workflow uses a SLAM-based algorithm to non-rigidly align datasets, improving efficiency, accuracy, and usability for complex multi-scan projects. Aura supports merging a combination of georeferenced and non-georeferenced scans, and outputs one .laz file per scan. The individual files can then be combined in Aura to produce a unified point cloud.

What you will need

Capture and system requirements

• Approximately 20% overlap between scans to support accurate alignment.

• Each scan processed individually in Aura before merging, according to its type.

• Sufficient available RAM. Avoid merging point cloud files that exceed available RAM, and use subsampled point clouds to reduce computational load.

Vehicle RTK, backpack RTK, and non-RTK scans can be merged together. RTK scans improve the alignment of non-RTK scans in areas where they overlap.

Scan processing requirements

Each scan must be processed in Aura before merging, according to its type.

Procedure

Step 1: Configure the merge job

1. Open Emesent Aura and click Process Scan in the top-left corner.

   

2. Select the Merge workflow in the Configure New Scan Job panel.

3. Click Add Datasets, then click Add next to Add dataset folder.

   1	ScanJob123/
   2	├── Output/

4. When prompted, select the Scan Environment that most closely matches the scan.

   

5. Wait for Aura to detect and list the available files.

   

6. Repeat steps 3 to 5 for each additional scan to include in the merge.

Select the offload folder containing the .bag files. Do not select the Output folder, as Aura will not detect the scan files.

Step 2: Choose an alignment base for preview

In the Alignment Preview File column, select any scan to use as the alignment base. This file is used for preview purposes only and does not affect the final output. Where available, Aura defaults to a subsampled version.

For RTK merges, select an RTK scan as the Alignment Preview File (satellite icon) to avoid unnecessary manual alignment.

Step 3: Configure overrides

Use Apply Overrides to configure scan-specific settings such as exclusion zones or trim data.

For RTK and RTK + non-RTK merges, verify that RTK scans have the correct georeferencing method and GNSS receiver type assigned. Aura applies these automatically.

Step 4: Select a reference scan (Optional)

For Non-georeferenced scans (Non-RTK) Merges:

• You can choose one scan to act as the reference scan. This scan will be locked in place, and all other scans will align to it.

For non-georeferenced (non-RTK) merges, one scan can be set as the reference scan. The reference scan is locked in place, and all other scans align to it. If no reference scan is selected, Aura performs pairwise alignment between all point clouds, which increases computational complexity and processing time.

If a reference scan is not selected, Aura will perform pairwise alignment between all point clouds. This increases computational complexity and may extend processing time.

For RTK Merges and RTK + Non-RTK Merges:

• Reference scans are supported for merges involving RTK scans. Proceed to Step 5.

Step 5: Configure processing settings

1. Define the location and name for the merged output.

2. Adjust the general merge and output options as outlined in the Aura User Manual, Section 3.3 (Process Tab).

For RTK and RTK + non-RTK merges, also configure the following:

1. Set the Base Coordinate Reference System to match the original horizontal CRS used during scan acquisition (for example, EPSG:4326, WGS 84).

2. To manually enter a full PROJ string, enable Custom base CRS.

3. (Optional) Enable Reprojection to transform the output into a different coordinate system, then define the Target Coordinate Reference System by selecting the desired horizontal and vertical CRS values.

Step 6: Review and manually align

Aura's SLAM algorithm relies on overlapping features between scans to perform a merge. When georeferencing is unavailable or inconsistent across datasets, manual alignment provides an initial position estimate, reducing drift and improving the merged point cloud.

Manual alignment is required in the following scenarios:

• Merging scans without georeferencing (for example, non-RTK).

• Merging georeferenced and non-georeferenced scans together (for example, RTK + non-RTK).

For RTK-only merges with correct setup, Aura indicates that no manual alignment is required. Skip to Step 7.

For RTK Merges:

• If setup is correct, Aura will notify you that no manual alignment is necessary and you can skip manual alignment and start processing.

Aura will attempt to merge scans even if they are misaligned, either horizontally or vertically. This can result in a skewed or inaccurate final output. Always verify alignment before continuing.

1. Click Load Scans to load all selected point clouds into the viewer.

   • Each scan is assigned a unique color to assist with differentiation and alignment.

   • To add or remove datasets from the current merge job, click Edit Point Clouds Selected.

Align scans manually using the Translate and Rotate tools:

2. • Start in Top View to position and rotate scans horizontally.

   • Switch to Front View to adjust scans vertically.

Click Reload Scans in the Configure New Scan Job panel to reset a scan’s position.

Step 7: Start the merge

1. Click Start to begin processing.

   

Start button not visible

If the Start button is hidden, click the Configure New Scan Job panel at the bottom of the window to reopen the Processing Scan panel.

Step 8: View and combine datasets

When processing is complete, Aura outputs one .laz file per scan to the directory specified in Step 1. Files are aligned using the SLAM algorithm and georeferenced where applicable. The outputs are grouped in the Merge Complete panel.

1. Click View in the Merge Complete panel to inspect each output dataset individually.

   

2. Minimize the Merge Complete panel to access the Visualize tab.

   

3. (Optional) Adjust the color of each point cloud in the Visualize tab to compare and validate the alignment.

4. Hold Shift and click each dataset to select multiple point clouds.

   

5. Open the Project menu and select Save As to save the combined dataset as a single point cloud.

Combine datasets later

1. Navigate to the Visualize tab.

2. Click Add to load previously processed .laz files.

3. Repeat steps 3 to 5 above to compare, validate, and save the combined dataset.

Outcome

The merged scans are saved as a unified point cloud, aligned using SLAM and georeferenced where applicable.

View the combined accuracy report (RTK only)

After processing an RTK merge, each scan generates a .csv accuracy report stored in the output folder of the individual scan. Multiple reports can be loaded into Aura to generate a combined accuracy report.

1. Open the Merge Complete menu in Aura. The menu appears automatically after processing, or click the Merge Complete bar to open it.

   

2. Click View on the right-hand side of any metrics.csv accuracy report to open it.

   

3. Click + CSV in the report window. Windows Explorer opens.

   

4. Navigate to and select any additional .csv accuracy reports to include.

5. Select the Combined Report tab to view the merged accuracy data.

Additional information

Colorize or extract 360 images

After merging, point clouds can be colorized using camera imagery. Follow the instructions in the Aura User Manual — Colorization Workflow.

Merge compatibility summary

Troubleshooting