Global Registration

Registration is the re-orientation of two or more objects (point or polygon) that comprise a single object, so that identical regions of different objects are made to coincide and a more complete composite object can be constructed (by means of Points > Merge or Polygons > Merge).

Tools > Registration > Global Registration automatically fine-tunes the orientation of two or more point or polygon objects (or selected subsets of those objects) so that identical regions match up as perfectly as possible.

This function cannot be un-done after OK is pressed.

The Global Registration dialog is divided into two tiles:

• Registration tile - presents controls and indicators for the registra­tion of two or more objects. Registration is the re-orientation of two or more objects that comprise a single object, so that identical regions are made to coincide and a more complete composite object can be con­structed.

•    Analysis tile - presents controls and indicators to analyze the devi­ation between objects

The controls on the Registration tile are:

• Registration tile - This is the set of controls when the Registration icon has been pressed.

•   Control group - permits registration controls to be set.

• Tolerance field - specifies the average deviation between points on different objects that causes the iteration process to stop.

• Max Iterations field - specifies the maximum number of iterations that will be performed in the attempt to reach the goals. If optimal registration is achieved, fewer iterations will be performed.

• Sample Size field - specifies the number of points from each point object that will be used to guide the registration process. A lower number may increase performance. A higher number may increase the accuracy of the registration.

• Update Display checkbox - specifies real-time display of the regis­tration process in the Viewing Area. Uncheck this box to increase per­formance.

• Object Colors checkbox - specifies whether to indicate each object with a vivid, contrasting color.

• Slip Control checkbox - activates an automatic translation-limitation. This prevents "featureless" parts such as turbine sections from slipping and sliding with respect to each other during the registration process and giving poor results.

• Limit Translation checkbox and Max Translation decimal field - is a "manual" form of Slip Control. During the registration process, no point of any involved object is allowed to move more than Max Translation. If Slip Control and Limit Translation are in effect simultaneously, the actual maximum translation is the automatic value or the manual value, whichever is less.

• Constraints group - applicable only when the two or more to-be-registered objects have at least one target (as generated by Tools > Registration > Detect Sphere Targets) on each. By using tar­gets as points of constraint during a global registration, two objects that are otherwise unsuitable for global registration become suitable. For example, two cylindrical objects are typically unsuitable for global registration because exact orientation cannot be achieved, but if each has a target that is known to correspond to the same target on the other, exact orientation can be achieved.

• Apply Datum Constraints checkbox - causes similarly situated targets on the objects to serve as constraints of the registration process. Before this Global Registration function is started, the two objects must be at least roughly registered so that the software can detect the correspondence of targets on the two or more objects. There must not be so many targets that the software can­not recognize the correspondence, and the targets must not be so close to each other that the software cannot distinguish them. This checkbox also activates the following controls:

• Strength (%) slider (0% to 100%) - is the priority that is placed on the registration of targets versus registration of the objects’ surfaces. Low strength applies low priority on the registration of targets and high priority on the objects’ surfaces. High strength pulls corresponding targets closer together, possibly at the expense of perfect registration of the objects’ surfaces.

• Datum Cluster Statistics checkbox - A datum cluster is the set of corresponding targets on the two or more objects. When activated, a label appears in the Viewing Area on each cluster. It is not neces­sary to press Apply button to change these settings. The contents of each label depends on:

• Average Distance radio button - Each label shows the aver­age distance between targets within a datum cluster.

• Maximum Distance radio button - Each label shows the max­imum distance between any two targets within a datum clus­ter.

• Statistics group - presents diagnostic details about the registration process. For greater detail, see the Analysis panel.

• Per Scan group - For each object involved in the registration, this sec­tion presents:

• Motion - a measure of the movement of this object in the last itera­tion. Typically, this value decreases with each iteration.

• Distance - the average deviation between this object and overlap­ping objects on the most recent iteration.

• OK button - stores registered objects to the Model Manager and closes the dialog.

• Cancel button - discards the registration and closes the dialog.

• Apply button - performs the registration as configured and leaves the dialog open.

The controls on the Analysis panel are:

• Analysis panel - This is the set of controls when the Analysis icon has been pressed.

•   Display group -

• All Objects radio button - specifies that the analysis will be per­formed upon all the scan objects.

• Single Object radio button - specifies that the analysis will be per­formed upon a single, selected scan object.

• Scroll arrows - Use these to select the single object for analysis.

• Density drop-down - (low, medium, high, full) selects the rigorous­ness of analysis.

• Compute button - starts analysis of selected scan object(s), puts results into the Statistics group, and generates a deviation spec­trum.

• Spectrum group - Deviation values are computed for points in overlap regions. A deviation value is the shortest distance from one point to a comparable point on any of the other scans.

• Spectrum Name dropdown - (Registration, indicating that the spec­trum is a default based on the registration deviations, or the name of a custom deviation spectrum designed with Analysis > Edit Spectrum.

• See All About Spectrums.

• Statistics group - indicates the Maximum Distance, Average Distance, and the Standard Deviation of points manipulated during the registration.

• OK button - accepts the registration and closes the dialog.

• Cancel button - discards the registration and closes the dialog.

• Apply button - no function.

To perform global registration:

1. Use Tools > Registration > Identify Groups if necessary.

2.  In the Model Manager, activate two or more groups or individual point objects.

3. Click Tools > Registration > Global Registration.

4. Adjust the settings in the dialog as necessary, then click Apply.

5. When registration is complete, click the Analysis icon to determine whether the registration is satisfactory, OK to save the point objects in their new positions, or Cancel to close the dialog without saving the point objects in their new positions.

To obtain visual feedback about the precision of a registration process:

1. If you clicked the Analysis icon, use the Display group to select objects for analysis, then press the Compute button.

2. If the Deviation Spectrum or the Statistics section indicate excessive deviation in the registration of the object, press the Registration icon to refine the registration. If registration is acceptable, press the OK button, note the properly registered objects in the Model Manager, and continue with Points > Merge or Polygons > Merge Polygon Objects.

See the settings at Tools > Options > Operations > Registration > Global Registration Parameters.