This page contains answers to common questions handled by our support staff, along with some tips and tricks that we have found useful and presented here as questions.
- Is Phase MOSAIC a phase shifting data acquisition program?
- How do I register surfaces together?
- Can I register surfaces without using fiducials?
- Graphics appear blocky on my display. Does this mean my results will be inaccurate?
- How are pixel values chosen for surface frame operations (registration, addition, subtraction, maximum, minimum,averaging)?
- I am Zernike fitting a surface and the resulting coefficients don't seem to make any sense. Whats' going on?
- After matching coordinate systems using fiducial groups, the surface now seems to be skewed. How can I stop this from happening?
Phase MOSAIC supports data acquisition with Phase MOSAIC AQ. This version works with a server program connected to phase shifting hardware. The client and server programs connect over a LAN connection. Extra functionality supported by Phase MOSAIC AQ is represented by the AQ symbol in this help documentation.
Surfaces are registered or "stitched" together by using coordinate systems. To start, make sure a proper global coordinate system is defined in each surface to register. One way to do this is to use fiducials. In each surface file, mark fiducial locations at known physical locations. Then use the Modify | Coordinate System | Match | Fiducial Groups | menu item. Edit the fiducial values in the group to match to be the known physical positions. Then fit the coordinate system to this group using the Match button. Be sure to save a version of the file with the corrected coordinate system for each surface to be registered. Load the first file and use the Modify | Pixels | Frame | Register menu item to select the other file. At this time you can select the aberrations to be adjusted to match the surfaces together.
Yes. Registration uses the coordinate system defined for each file. If each surface to register uses the same set of pixel locations, the default coordinate system on each surface can be used to register since it will be the same. One limitation to this is allowing aberrations higher than focus to be adjusted during registration. Higher aberrations require a correctly identified center. In this case, the center that is used for registration needs to be the optical center of the part registered.
Not necessarily. Phase MOSAIC uses the "document-view" model of programming. This means that the data and the display of the data are separated. Calculations in Phase MOSAIC use the actual pixel values, not the displayed pixels on the screen. Graphical display of data can appear blocky if the graphics resolution setting is much lower than the number of pixels being represented. The graphics resolution of the 2D surface view can be adjusted by right-clicking in the view and select the Properties menu item. The render resolution can be changed with the Preferences tab. This adjusts the desired resolution of the graphical representation of the pixel data. For more information, see Plots and Views.
These operations work by choosing a surface height from the surface to be registered, (or added, subtracted, etc.), and modifying the base surface height based on this value. Generally, surface height can be chosen by finding the nearest pixel value to the desired location, or interpolating the value. Interpolation may result in more accurate results in some situations, but may also result in smoothing of the surface data. For this reason, Phase MOSAIC chooses the pixel overlay value by finding the nearest pixel value to the desired location. If interpolation is desired, it is recommended that the surface be resampled to a square grid using the Modify | Pixels | Resample | Square Pixels | command. Be sure to check the Use Bilinear Interpolation checkbox. Frame operations can be executed on the resampled surfaces after saving.
Phase MOSAIC fits Zernike polynomials around the currently defined coordinate system origin. By default, it then defines a normalization radius to be the distance from the origin to encompass all of the valid pixel data. If the origin of the coordinate system is far from the centroid of the valid pixel data, the data will be non-orthogonal and the resulting fit coefficients will not appear to be correct. In order to evaluate Zernike polynomial coefficients for an arbitrary surface, translate the origin of the coordinate system to the centroid of the valid data using the Modify | Coordinate System | Translate | To Centroid menu item.
Phase MOSAIC uses a least-squares optimization to match fiducial groups containing 3 or more fiducials. This results in all six coefficients of the affine transform matrix being treated as free parameters. This means translation, x- and y- scaling, rotation, and x- and y- skew are allowed in the fitted transformation. If only translation, scaling, and rotation are allowed, match fiducial groups containing only 2 fiducials. The 2 fiducials can be created from average positions of a larger number of fiducials. If only translation is desired, match fiducial groups containing only 1 fiducial.