Voxel Cloud Display

Voxelization (enabling the voxel processing) provides an alternative to using the Cloud Display Control to help visualize large point cloud files by providing a 3D grid or volume based sub-sampling option. It also provides an alternative to vectors for displaying cloud to object deviations or other Surface Analysis displays

How it works is you specify a grid size or volume and then only the point closest to the average for a specified volume, which we call a “voxel”, is displayed. Displaying a cloud in this way creates a roughly uniform density display of cloud data cross the entire scan region, and the size of the voxel point (displayed as a screen oriented disc or blotch) can be adjusted as a percentage of the volume used in its computation.

 

Enabling Voxel Display for an Existing Cloud

The Voxel cloud display can be enabled either through a cloud’s properties or as an alternative vector display option from within a Cloud to Objects relationship

The Voxel Setting dialog provides the ability to adjust the display as needed with the following controls:

Traditional vectors reports consider cloud point deviations no different than points. You can sub-sample and you can ignore edge projections but its still just considering the points directly. Voxels are different. They are volume oriented. In each voxel volume the cloud points are processed and only the single cloud point closest to the average in that volume is considered. This dramatically down samples the cloud statistics and distributes the analysis much more equally across the part. In addition there is some built in outlier rejection. If a considered volume only has 1 or 2 points it, it will be ignored, which is ideal for ignoring noise from a scanner. This is an adjustable threshold (Min Point Count Per Voxel) that defaults to 3. If you set this value to 6 for example there has to be 6 points in that volume or no voxel will be built in the zone. The advantage in this method is that it is not just smoothing by a distance but instead it preserves the actual scanned data. If there is a blemish in the part then removing outliers by a distance threshold may hide those bad places on the part. Voxels will not.

If you change the Min Point Count Per Voxel to 1 and turn the option to ignore edge projections off you should see the Total and Valid point counts are equal

This statistic is basically telling you how many voxel volume’s were processed and ignored. The Voxel Size defines the volume considered so with larger point clouds you will want a larger volume. For quick graphics displays it seems that keeping the total displayed number of voxels to roughly 200K is a good rule of thumb for a reasonable laptop. The Auto Detect button tries to do that for you but is generally a little conservative.

 

Voxel Display Settings

The Voxel Display Settings are used to control the color and size of the blotch used to display the voxel.

 

Using Voxel Colors for Deviation and Analysis

Surface Analysis Mode

Each voxel point can be colorized to display different information us- ing the following settings:

The voxel processing takes place following the scan data arriving in SA so you will see a scan pass line appear first and then be converted to a surface voxel as you scan.

Basic Cloud Display Controls & Part Comparison In SpatialAnalyzer -

https://youtu.be/IzTV3lK4rVg

 

Simple Surface Deviation Display Process

To visualize the deviations between a cloud and a CAD model using Voxels follow these steps:

  1. Import the CAD Model, scan the part and align to it. Then dis- connect from the instrument.

  2. Build a Cloud to Objects relationship between the cloud and the CAD model.

  3. Open the Relationship properties and enable the Voxel Cloud Display. Select Voxelized Cloud Settings to adjust coloring or tolerance settings

  4. To add callouts displaying voxel deviation at particular locations, right click on the relationship and select Add Voxel Callout

 

Voxel callouts can be added through the right-click properties of a Cloud to Objects relationship or through the standard Callout drop down list. When you add a voxel callout you select a zone of voxels depending on how closely you are zoom in or out. The callout will by default identify the highest and or lowest voxel value for that region assuming all the voxel deviations are the same sign. If your selection bridges a zone where there are positive and negative values in that selection the callout will also display both the high and low values. The leader line will attach to the specific voxel being reported if selected directly or include a region based upon the zoom extent at the time the callout was added.