--- title: "How do we know if a SLAM is drifting or broken?" slug: "how-do-we-know-if-slam-is-drifting-or-broken-1" description: "Learn how control points enhance scan accuracy and when they can't fix drift or breaks in SLAM, especially in challenging environments." tags: ["Control Points", "Fly away", "G10", "G11", "G9", "Scanning Accuracy", "SLAM break", "SLAM drift", "SLAM Error", "Troubleshooting", "twisted"] updated: 2026-07-03T07:49:51Z published: 2026-07-03T07:49:51Z canonical: "knowledge.navvis.com/how-do-we-know-if-slam-is-drifting-or-broken-1" --- > ## Documentation Index > Fetch the complete documentation index at: https://knowledge.navvis.com/llms.txt > Use this file to discover all available pages before exploring further. # How do we know if SLAM is drifting or broken? Using control points (also called checkshots or check points) during a scan helps improve Point cloud accuracy. However, the use of control points cannot always prevent twisted or tilted scans. This article describes when control points can improve your scanned data and in which scenarios they cannot. The NavVis device uses an algorithm called Simultaneous Localization and Mapping (SLAM). You can find more information on SLAM here: - [https://www.navvis.com/technology/slam](https://www.navvis.com/technology/slam) - [https://www.navvis.com/blog/how-slam-affects-the-accuracy-of-your-scan-and-how-to-improve-it](https://www.navvis.com/blog/how-slam-affects-the-accuracy-of-your-scan-and-how-to-improve-it) - [Common Causes of Poor SLAM Results and How to Solve them](/v1/docs/challenges-in-mobile-scanning) ## SLAM Drift During NavVis Post-Processing, control points are used to eliminate drift within the walked trajectory during the scan. A drifting SLAM is more common in outdoor environments due to the size and because the scanned loops are often made bigger than when indoors. Drift means that the scans were correctly matched to the map, but each scan has some distortion due to small accumulating errors over time. Using surveyed control points (sometimes called checkshots or check points) during post-processing will generally be able fix a drifting Dataset. Drifts can be recognized by: - A consistent and continuous trajectory. - Long straight walkways or corridors being slightly tilted along the whole distance (not in one exact spot). - Larger loops not closing in the same location. ## SLAM Break In more challenging environments the SLAM can break. This means that during scanning the maps are matched incorrectly, e.g. because of insufficient distinctive features in the environment or in very noisy environments. Using control points with this type of issue will not help. In most cases a break can be recognized by: - A jumping trajectory. - Duplicated structures like buildings. If the SLAM breaks, there is a possibility it can be fixed during post-processing, but in extreme cases it cannot. In such situations, control points will be not able to correct the breaking trajectory since there is no data on how to distribute the difference in distances between the control point coordinates and the scanned control point coordinates. --- ### FAQ #### What are control points used for in scanning? Control points help improve the accuracy of point clouds during a scan. #### Can control points fix all types of scan issues? No, control points cannot always save twisted or tilted scans. #### What is SLAM in the context of NavVis devices? SLAM stands for Simultaneous Localization and Mapping, an algorithm used by NavVis devices. #### How does SLAM drift occur? SLAM drift occurs when there are accumulating errors due to imperfect sensors, especially in outdoor environments. #### What are signs of SLAM drift? Signs of SLAM drift include a consistent trajectory, tilted long walkways, and larger loops not closing in the same location. #### What happens when SLAM breaks? When SLAM breaks, maps are matched incorrectly, often due to insufficient distinctive features or noisy environments. #### Can control points help if SLAM breaks? No, control points cannot correct a breaking trajectory if there is no data on how to distribute the differences. #### How can I recognize a breaking SLAM? A breaking SLAM can be recognized by a jumping trajectory and duplicated structures like buildings. #### How do I perform checkshots? A checkshot (also called a check point, checkpoint, or control point verification) involves placing the scanner at a known location and capturing the coordinates to verify scan accuracy. For step-by-step guidance on placing and using control points, see [Introduction to Control Points](/v1/docs/an-introduction-to-control-points). A Point Cloud is as a collection of data points in space that typically represent the external surface of an object or environment. Point clouds are used in various applications, including 3D scanning and mapping, and can be visualized and manipulated using Navvis IVION. You can perform actions such as panning, orbiting, cleaning up noise, cropping, and downloading data in formats like .e57 or .ply. The resolution of point clouds processed with NavVis Software achieves a minimum detail of 5mm, indicating the precision of the spatial data points. Simultaneous Localization And Mapping A dataset is a piece of a site, the result of a continuous recording with a NavVis mapping device or the result of an imported point cloud. Datasets can contain panoramic images and point clouds.