Explanation 

Holes 1, 2 and 3 are used to control the Primary Plane in this example this is the X+ Plane. From Point 1 to Point2 defines
the Y+ axis. These five features are controlling the orientation
of X+ and Y+ axis, Z+ follows the Right hand rule. These features do not control the Origin of the Alignment in these
Axis' this can be done using additional features if required.  
The Tertiary Point defines the Origin and offset (if any) for X,
Y, Z, these Features do not control the orientation of the axis ONLY the origin of each Axis. In this example, the Origin (0.000) of X is a circle named XOriginPoint, while Plane1 is the origin (0.000) of Y, and the cylinder named Shaft1 is the origin (0.000) for Z. 

As defined in the Feature Align dialog the X+ axis is in the vector direction of Holes1, 2 and 3 with its origin at XOriginPoint, the direction of Y+ is defined from Point1 to Point2 with its origin being on Plane1, and finally Z+ following the right hand rule has its origin in the center of the Cylinder named Shaft1. 

Creating a Reference System from a Feature Alignment 

When measurement tasks require Alignments be performed using "Features" that are not easily measured or may not be measured in the future due to construction a "Reference System" may be established that will provide not only a method to more precisely Align to the object, but a method to monitor movement in components. 

By measuring "Reference" points (points that will NOT move") in conjunction with the Feature Alignment features (or points used to fit features), the Reference Points can be valued relative to the Feature Alignment. By Exporting, these aligned "Reference Points" to a .CSV or Excel file ALL future Alignments may be performed by importing the Reference Points and doing an AutoAlignment in Verisurf X. 

Benefits of using a "Reference System" 

The Feature Alignment process must be completed only once eliminating the need to measure the Features (or points used to Fit Features) each time an Alignment must be performed. 

On structures or machines where the Alignment Features are NOT tied together mechanically, they move independently, when performing Feature Alignments this movement is not easily detectable. However, when using Reference Points and an AutoAlignment the results are shown in X, Y, Z, 3D deviations relative to the "nominal" value, giving the operator the ability to monitor the movement in an object constructed of multiple components.

With proper installation of the "Reference Point" monuments, any subset of the points can be AutoAligned to; this allows work to be performed locally as the entire Object does not need to be measured to perform the Alignment process. 

Increased precision of Alignments - when Feature Alignments are performed they are typically controlled using a 3-2-1 method, with the origin being known in three directions, the axis known in two directions and the plane known in one, this provides a total of six "transformation" parameters to complete the Alignment process. As each of the saved Reference Point is known in X, Y, Z when performing an AutoAlignment Verisurf will utilize these 3 parameters from EACH Reference Point during the AutoAlignment process. Therefore, if 7 Reference Points are measured 21 Transformation parameters will be used to solve the Alignment (7 points, 3 parameters each = 21), giving a much higher precision than a Transformation using only 6 parameters.

Reference System Suggestions 

Place "Reference Points" in high visibility, stable locations to allow measurement from multiple device locations.

If a Reference System will be established it is recommended that, a verification survey is performed following the initial valuing using the Feature Alignment process. This ensures that the repeatability of the Reference Points is within expected tolerances and that the initial Feature Alignment was performed correctly. 

If measuring a large object in an area where the temperature is not controlled, the use of Object Temperature during the initial measurement process is recommended, all following AutoAlignments would use "Scale" when they are calculated. Proper implementation of Scale will provide precise Alignment results regardless of object temperature. 

For more information on Verisurf, visit http://www.mcamnw.com/verisurf.html or contact Mike for a quote.