Control Point Types: Surveyed and Alignment Markers

NavVis Cross-Dataset Alignment (CDA) processing supports two types of control point: surveyed control points and alignment markers. Both are physical markers placed on site and captured by the NavVis device during scanning. The difference is whether the control point has known coordinates. Surveyed control points have coordinates measured by a total station or other surveying method, in either a local or georeferenced coordinate system. Alignment markers have no associated coordinate file.

Alignment markers

Alignment markers (also known as targets, tie points, or unmeasured control points) are the simplest form of control point. When the device captures them during scanning, no coordinate file is involved.

When to use alignment markers

• You need to stitch multiple datasets together using CDA.
• No surveyor or survey equipment is available.
• Georeferencing is not required.

When not to use alignment markers

• You need to verify absolute accuracy against known reference points.
• The project requires georeferenced data (for example, for BIM coordination or regulatory compliance).
• You need to anchor data to a specific coordinate system.

Surveyed control points

You measure surveyed control points with a total station or another surveying method and upload them as a CSV or TXT file when creating a processing task. Surveyed control points georeference datasets by anchoring them to real-world coordinates. They can use either an arbitrary local coordinate system or a global geodetic survey system (called a Spatial Reference System in NavVis IVION). All control points in a project should be in the same system.

When to use surveyed control points

• You need georeferenced data (for example, tying data to a geodetic or site coordinate system).
• You need to verify absolute accuracy against known reference points using the Control Point Verification Log.
• You are aligning scan data with GIS, CAD, or BIM models that use a specific coordinate system.
• The project has regulatory or contractual accuracy requirements.

When not to use surveyed control points

• You only need to stitch datasets together without georeferencing. Use alignment markers instead.
• No surveyor or total station is available on site.
• The project does not require accuracy verification or a specific coordinate system.

Quick reference

Capturing control points on your device

For more information on how to capture control points on your device, see:

• NavVis MLX Control Point Capturing and Management
• NavVis VLX Control Point Capturing and Management