Markers for 3D scanning: how to choose and place them correctly

What are positional markers used for in 3D scanning, how to select and place them on a part, tooling, and a large object, and how to verify the results.

Position markers are not needed for every object. They help the scanner maintain position on flat, solid‑colored, and repetitive surfaces, on large parts, and when shooting in multiple positions. In this article, we will look at when markers are needed, how to select and place them, and how to check the result. General preparation steps (cleaning, working area, calibration) and matte sprays are described in the article “How to prepare an object for 3D scanning: matting spray”

Markers in 3D scanning: a brief overview

markers do not improve the visibility of the surface itself; they provide the system with stable reference points for more accurate and correct data collection about the object’s geometry.
markers alone do not increase the scanner’s accuracy, but they help maintain it.
spray and markers serve different purposes and can be used separately or together.
there is no universal scheme for placing markers: the type, size, and required number of visible markers are determined by the scanner model, the working area, and the selected mode.

What are markers used for in 3D scanning

Position markers are markers recognized by the scanner; based on their relative position, the system determines the position of the frames or the scanner. They are especially useful on flat, uniform, and repetitive surfaces where there are too few geometric features.

Markers work only in a static and unchanging scene. If the marker has shifted relative to the object, the reference coordinate system becomes unreliable.

Different technologies use different markers: white, contrasting, or retroreflective, adhesive, and magnetic, in several diameters. The most common diameters are 3, 6, and 12 mm. Compatibility must be checked according to the scanner’s manual. The RangeVision page lists markers of various types and sizes for the corresponding equipment modes. RangeVision Helix and RangeVision Fenix handheld laser scanners, as well as the stationary RangeVision PRIME, support marker operation, and all models are listed in the 3D scanner catalog.

Different marker sizes are supported by various 3D scanners

When markers are needed

Markers are needed when the scanner has nothing to latch onto in the geometry or when the object is too large for a single position: on flat, solid‑colored, and repetitive surfaces, on large parts and assemblies, and when shooting from multiple positions. If the reason for data loss is glare, transparency, or a dark surface, markers will not help: here, a spray or another scanning mode is required.

Geometric markers not only create a reference network around the object but also add geometry that makes it easier for the scanner to orient itself.

When you need a spray, markers, or both

Placement of markers

The part must not shift relative to the markers, the turntable, or the external support frame during scanning. At the same time, the clamp must not alter its shape. This is especially important for thin‑walled parts, rubber, soft plastics, and long elements.

If the object needs to be rotated, determine the overlap areas and the method for aligning the individual scans in advance. Markers located only on the table or the substrate around the object are helpful as long as the relative position of the table and the part does not change. If the scanning program supports working with groups of scans, the object can be captured in several positions, with a separate set of marks for each, but when aligning the groups, you will mainly rely on geometry for orientation.

How to place markers correctly

Arrange the markers irregularly, without straight lines, symmetrical grids, or repeating shapes.
Ensure a transition from one group of markers to the next along the entire scanning route.
Make sure that each frame contains the required number of markers for the specific mode. Some laser scanner manuals require at least four markers to be visible, but this number cannot be applied to any device.
Do not attach markers to highly curved areas if the sticker deforms and is no longer perceived as a circle.
Do not cover edges, holes, and small elements that need to be measured with marks.
Do not use damaged, dirty, or partially detached marks.
At transitions across a large angle, increase the density of the marks so that some of the reference points remain visible from both directions.
For a small part, place the marks on a fixed tooling or table if their relative position to the object will not change.
For a sensitive surface, use a coordinated protective tape, magnetic holders, or an external frame instead of direct adhesion.

If both a spray and markers are needed at the same time, usually an even coating is created first, and then the markers are applied: spraying over the markers may impair their recognition. However, the adhesion of the stickers to the specific coating must be checked. For information on selecting and applying the spray, see the article on preparing the object.

The shiny metal part is coated with a matting layer, over which markers are attached: the object’s geometry is too simple to do without them

Preparation of large objects

When scanning a body, engine, mold, or large assembly, a single local group of markers may not be sufficient. A continuous reference network along the entire route is required. To improve the stability of spatial referencing, photogrammetry, code markers, and scale rulers can be used.

The RangeVision material on 3D scanning with photogrammetry demonstrates the workflow: cleaning complex surfaces, matting, applying process and code markers, installing scale rulers, building a reference network, and subsequent geometry capture. This scheme is not required for every large object, but only when the requirements for size, route, and dimensional accuracy justify an additional stage.

Before applying markers to a vehicle, a painted body, or a finished product, the method of attachment should be agreed upon. In practice, markers can be placed on safe masking tape or removable magnetic carriers, provided this does not violate the requirements of the specific system.

Reusable magnetic markers are easy to apply to the metal body of a car, and, most importantly, they are just as easy to remove after scanning

How to check the placement of markers

The placement is considered complete if the test pass confirms two conditions simultaneously:

Positioning stability. The system does not lose tracking while moving along the planned route.
Preservation of geometry. The fasteners and markers do not obscure critical elements and do not deform the object.

Common mistakes when using labels

Attempt to correct glare with markers
Markers help position the frames, but they do not make a mirror‑like or transparent surface accessible for digitization. To achieve this, the scanning mode or settings, or the optical properties of the surface, are changed.

Place markers in rows
A regular pattern creates ambiguous combinations. Markers should be distributed irregularly, while maintaining continuous visibility of the reference points.

Move the object relative to the markers
If the marks are on the table, but the part has moved, their coordinates no longer describe the position of the part. The data set needs to be re‑taken or divided into correctly aligned projects.

FAQ — common questions about markers

There is no fixed number per object. It is more important that the scanner consistently sees the required number of uniquely positioned marks when moving between areas. The specific minimum, diameter, and permissible density depend on the model and mode; they are taken from the equipment manual.

Video Tip

Conclusion

Markers are needed where the scanner lacks geometric features for stable positioning: on flat, monochromatic, and repetitive surfaces, on large objects, and when shooting from multiple positions. Place the markers irregularly, ensure continuous visibility of the reference points, and do not shift the object relative to the markers. Before the main scan, check the placement with a trial run.

If the object cannot be safely processed or the requirements for the result have not yet been formalized, the methodology can be tested on a demonstration fragment, or the task can be handed over to RangeVision’s 3D scanning specialists.