SDX-Compact: Scans differ in height after SLAM processing

If high-resolution scans of the same flat area differ in height, check whether SLAM was used to process them. SLAM needs distinct 3D features to align scan data reliably. On mostly open, flat ground with few features around it, SLAM can add height differences instead of removing them.

What you see

Scans of the same flat area may show different heights, and objects in the processed point cloud may look noisy or distorted. You can see the difference when you compare the scans in SDX-CAD or against known points.

Why it happens

SLAM aligns scan data by matching 3D features in the scene. On open, flat ground there is little geometry to match, so the alignment can drift. With SLAM off, processing uses the system's recorded positioning without SLAM-based alignment corrections.

Check whether SLAM was used

Open the project and go to Settings > Systems, and look at the SLAM mode column for the system that captured the scan.
Open the Data models list and look at the SLAM mode column of the high-resolution data model.
Open the processing report of the high-resolution run. It shows whether SLAM was active.

SLAM is a setting per system within a project. The setting of the system supplies the default for new projects, and the setting in the project controls processing. Changing it does not change a model that is already processed.

What to do

For future scans: turn SLAM off for the system in the project's system settings before the data is processed, if the scene is mostly open, flat ground.
For models that are already processed: contact Sodex Support. Support can check the processing report and, if needed, process the data again without SLAM. You cannot do this yourself.

Recalibration does not address SLAM alignment errors caused by insufficient scene features. If height differences remain when the data is processed without SLAM, contact Sodex Support to check positioning and calibration.

What to send to Sodex Support

The SDX-Cloud project link and the names or links of the affected data models
The system serial number
The scan date and approximate time
A description of the scene, especially whether mainly flat ground was visible
The measured height difference, the unit, and where and how you measured it
Screenshots that show the issue
The processing report, if available
Independent check-point measurements, if you have them
Whether the difference also appears when the data is processed without SLAM

Plan the next scan

This applies to high-resolution processing of SDX-Compact scans. Use SLAM when the scene shows distinct 3D geometry, such as buildings, walls, or piles. For a scan of mostly open, flat ground with few features around it, process without SLAM.