Appendix
Glossary
Terms as this manual uses them. Where SurView's own screens use a different word for the same idea, that word is given alongside it.
- Reference image
- The photograph taken before deformation. Every displacement in a run is measured relative to it.
- Target image
- A photograph taken after some deformation has occurred, compared against the reference (or, after reference updating, against a previous target) to measure movement.
- Subset
- The small patch of pixels around one measurement point that is matched between the reference and the target. Its size is the subset radius.
- Grid step
- The spacing, in pixels, between neighbouring measurement points.
- Correlation coefficient (ZNCC)
- A number stating how closely a candidate match in the target resembles the original subset in the reference. A measure of matching confidence, not of physical correctness.
- Displacement field
- The measured movement, in pixels, at every point of the grid.
- Strain
- Local stretching or shearing, fitted from the displacements of neighbouring points rather than measured directly at any one point. Reported in three common forms: Cauchy (small-strain), Green-Lagrange, and Euler-Almansi, which agree closely at small deformations and diverge at large ones.
- Region of interest (ROI)
- The boundary restricting where measurement points are placed, drawn by hand or proposed by automatic segmentation of the speckle quality. May exclude one or more holes: places inside the outer boundary that are not to be measured.
- Sequence
- A reference image plus an ordered series of target images, making up one loading test.
- Reference updating (re-anchoring)
- Switching a sequence's comparison from the original reference to a more recent frame, once too little of the field still correlates against the original. Off by default.
- Recovery pass ("Points that failed" in the Analysis panel)
- A second attempt at points the first correlation could not measure well, seeded with a displacement fitted from nearby reliable points and then fully re-solved. On by default; never accepts an answer worse than the one it would replace.
- Noise floor (sigma)
- The finest displacement a given subset's own speckle quality could resolve against the camera's sensor noise. A lower bound, computed from the reference image alone.
- Match conditioning (beta)
- How sharply the matching cost rises around the solution actually found for one point. Meaningful only within a single run.
- Virtual extensometer
- Two points placed on the measured field whose changing distance apart is plotted against frame, standing in for a physical clip gauge.
Where to find it on screen
| To do this | Look here |
|---|---|
| Import the reference or target images | Toolbar: Reference, Target |
| Draw or auto-detect a region | Toolbar: Define ROI, Auto-detect ROI |
| Exclude a hole from a region | Toolbar: Add Hole (needs a region first) |
| Choose the solver, subset, grid step, strain settings | Analysis panel |
| Turn reference updating on and see its cost | Analysis panel, "Reference" group |
| Turn the recovery pass on and adjust it | Analysis panel, "Points that failed" group |
| Start or stop measuring | Toolbar: Run Correlation, Stop |
| Read a value at one point of the field | Point panel; hover the field, click to pin |
| Switch between displacement, strain, and reliability channels | The "Showing" selector above the field |
| Place a virtual extensometer | Toolbar: Extensometer, then two clicks on the specimen |
| Plot a quantity against frame | Plot panel |
| See provenance for an imported image | Record panel |
| Export a field | File menu: .vtu for ParaView and FreeCAD, or .csv |
What is not in this manual yet
Written up only where the screen it describes actually exists, this manual is necessarily behind SurView's own roadmap. As of this writing, the following are real, tracked work that simply has not landed:
- Stereo and out-of-plane (2.5D) measurement, and the camera calibration workflow it depends on.
- Reading a quantity along a line, rather than only at one point or between two extensometer anchors.
- Multi-view measurement from a single moved camera, for slow or static tests such as creep.
- Sparse point-marker tracking, alongside the dense speckle field.
See ROADMAP.md for the current state of each. This manual will gain a chapter for each one as it ships.