It is often necessary to be able to take measurements and compute point location is in places that cannot be directly reached or measured. Hidden-Point Bar definitions provide a means to do that. Hid- den points can be computed in two ways:
Using a Hidden Pt. to SA measurement profile with a laser tracker. This is a direct measurement process defined within the measurement profile.
Using the Hidden-Point Bar Database saved within the SA Users Options. This has the added advantage of being a dynamic process that can be recomputed at any time. These options are described in the following sections.
Hidden point positions are dynamic. The naming convention can be used to compute an offset point and this happens automatically when points with the given name are a measured from an instrument. There is also a button to trigger an update for all hidden point bar definitions in a job file that can be found on the instrument tab under Instrument Shots:
The Hidden-Point Bar Database offers a list of hidden point bar definitions. A single default 2 point bar is available as a reference only. Use the Edit and Delete buttons to edit or remove the selected bar.
The list of Hidden Point bars can be Imported or Exported as needed using an XML format.
Bars can be defined in either of three ways through the buttons at the top right of the dialog:
Add Gravity Frame. A gravity frame is a single point offset point. Added to support survey applications it can be used to compute the location of a point shifted a predefined distance along the Z axis of a reference frame.
Add 2 Point Bar. Define the distance of a third point (C) based upon the vector between the two measured or selected points and the entered distance from one of those points (A or B) .
N-Point Frame. With 3 or more points defined, a 3D position can be computed anywhere in space relative to the measured or selected points. N-Point Fixtures are defined by selecting a set of points and also selecting a measurement location to return when those points are measured.
The most effective way to use hidden point bars or fixtures is to use a naming convention to designate points as part of a defined hidden point bar or fixture. To do so follow this naming convention:
Point Name $ (Bar Index) _ (Point Index)
Point Name. The point name for the computed point should also be used for all the measurements of the reference points used to built it.
Bar Index. The Hidden Point Bars defined in the user options are not named but instead use an integer index. By specifying “MyPoint$0_0” you are specifying a point named “MyPoint” and telling SA to use the “0” index bar.
Point Index. Its important to specify a measured point as A or B for a 2 point bar to be computed correctly. Also the specific index of the points within an N Point Bar need to be defined. The final piece of the naming convention is the point index. So “MyPoint$0_1” tells SA to use the 0 index bar and that this point represents the “1” index point.
If this naming convention is followed hidden point locations can be updated/recomputed at any point by using the menu command Analysis>Re-Compute Hidden Points. This can be quite helpful if hidden points are computed from multiple instrument plants and their relative positions are changed do to an alignment.