About Laser Stripes On Cylindrical Tube Shapes

Laser stripes from the scan arms comprise a string of points in space. You can see how VTube-LASER scans the stripes for the cylinder in this image.

How VTube Uses Laser Stripes On Cylindrical Tube Shapes

Laser line scanner stripes form a polyline with a maximum curve on a tube when scanning a diameter.

Because of this, VTube expects a natural arc to occur as the scan line wraps around the diameter.

If any point departs too far from this path, the spike filter automatically removes outlier vertex spikes in cylindrical laser stripes.


 

It Finds Outliers called "Spikes" in the Curve

An outlier is detected when the angle between three adjacent points exceeds a user-entered Spike Angle value. The default value is 15 degrees.
No matter how the operator positions the laser line on the tube, the angles between these points should never exceed a limiting angle.

The two points shown in the middle of this illustration are points that VTube-LASER would remove from the scan data - because the angle exceeds 15 degrees.

The only case where this isn't true on a cylinder is if the cylinder contains deformations like pits and raised bumps. In that case, VTube-LASER may remove the holes, valleys, or raised bumps - which is helpful.

Handling High-Reflectivity Surface Spikes

The other situation where the laser scanner might see spikes is when measuring a highly reflective tube. The points returned from the tube surfaces from highly reflective diameter regions may be registered as spiking away from the diameter. This filter removes any data that spikes away from the curve before it is given to the VTube-LASER math engine.

Note that this issue is especially true for older generations of scanners. Any scanner released before 2020 may be subject to many more fliers during scanning. For example, this was a problem with FARO Edge arms and older. This filter is essential for scanning if you use a FARO Edge arm of any generation.

When to Increase the Spike Filter Angle

Doing what is described here is very unusual - but giving an example will help demonstrate how the spike filter works. 

If you measure a small diameter and/or have the maximum point-per-stripe count set very low, you will want to increase the spike filter angle value.

See the image on the right for an example. If you cull the point count down to three points per stripe, the angle between the 3 points on the diameter will almost always exceed 15 degrees. The angle would need to be increased to 80 or 90 degrees to measure the tube using this configuration.

How to Change the Cylinder Laser Spike Filter Angle

Edit the value at row 17 in the Measure Setup / Laser tab menu. This value is saved per project.