For 3D instruments (e.g., Trackers) transforming objects in real time requires at least three on-line trackers. This functionality is often referred to as Trans-Track.
Each instrument will monitor and update a point. The movements of the set of points are used together to update objects in 6D. Select one point per instrument. The point selection order must be consistent with the Instrument selection order e.g., select the points in the instrument sequence. After defining the instruments and tracking points; select the objects that need to move with the point set. The Trans-Track interface (shown below) indicates the instruments being monitored and the respective fit error for the point that it is tracking. The time lapse value indicates the time lapse between the measurements (i.e., synchronization error).
SA has the capability of synchronizing three degree-of-freedom measurements from 3 or more instruments and combining them to calculate a six degree-of-freedom transformation. For Trans-Track to function correctly, three or more instruments must first be tied to a common coordinate system. This can be achieved using any accepted technique, such as USMN, bundling, or best-fit. Once the instruments are tied together, each instrument must measure a single point, which becomes the reference point for that instrument.
The Trans-Track operation is then started, and the instruments are simultaneously polled for updates. A real-time transformation is then calculated, and that transformation is applied to any objects of choice.
Ensure that you have three or more instruments tied together to the same reference system (usually a set of common points), and that their interfaces are all running in SA.
Affix three targets to the moving object, with one instrument watching each target--these will be your reference points.
Measure a single reference point from each of the instruments.
From the menus, select Move Objects in 6D Using Multiple Instrument Updates
When prompted, select the instruments that will be part of the operation. You must be explicit about the order in which you pick the instruments and pick them in an order that you will remember.
Now select the earlier-measured reference points that correspond with the instruments. The points must be selected in the same order as the instruments. (That is, select the first instrument’s reference point first, then the second instrument’s point, etc.)
When prompted, select the object or objects to which you’d like the transformation applied. The Transform Using Multiple Instrument Updates dialog will appear:
Click the Query Instruments button, and SA will begin polling the instruments and calculating the transformation. The dialog will list the fit error between the live set of points and the reference set. The time lapse among the measurements is also displayed. Measurements cannot be perfectly synced, therefore slower movement will result in more accurate real-time transformations due to a smaller time delay among the instrument measurements. Allowing the targets to become stationary for a moment will remove sync-based error from the transformation.
The Trans-Track dialog also has a few settings that can be modified:
Point Best-Fit Error Tolerance. If a point’s best fit error to the corresponding reference point exceeds this threshold, the point will be highlighted as a warning.
Time Lapse Tolerance (sec.). If the time difference between the first point and another point exceeds this threshold, the point will be highlighted as a warning, indicating that the measurement sync was not acceptable. This can be ignored when- ever the targets are stationary.
Delay after update (sec.). The time delay between one set of measurements and the next.
Trans-Track can be accomplished with a single instrument if the instrument supports a 6D target. Examples are the Leica T-probe/T-Mac, API STS and GSI V-Stars Phtogrammetry. These instrument can monitor and measure in 6D. The functionality is identical to Multiple Updates except that it is completely dependent on the 6D measurements of a single instrument. This makes setup much easier but may not offer the same degree of angular precision as can be obtained using multiple instruments.
Some instrument systems, such as photogrammetry systems, are capable of tracking several points simultaneously. SA is capable of watching this batch of points and updating the transformation of one or more objects as the updates arrive. Since this command only involves one instrument, alignment among multiple instruments is not required as it is with Transform in 6D Using Multiple Instrument Updates.
From the menus, select Move Objects in 6D Using a Batch of Points from an Instrument.
Select the object(s) that you would like to transform. The Trans-Track a Point Set dialog appears will then appear.
Before moving anything, measure a set of points. This will be used as the reference for the initial position.
As each set of measurements are taken, the position of the selected objects will be updated, and the fit error will be re- ported in the dialog.
When finished, click Done: Leave Objects in Current Position to accept the transformation, or Cancel: Restore Object Positions to cancel the command and put all objects back into their original positions.
Relationships are dynamic by nature and work great with Trans- Track. Watch windows can be displayed for relationships which will allow real time monitoring while moving. shows an example of Trans-Track being used to join two cylindrical sections. A frame to frame relationship was used to monitor the position and orientation of the moving unit with respect to its final nominal location.