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UniVert User Manual
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6. Modify search parameters:
Source
Template The optimal source template is difficult to predict, but in general it is
advantageous for the template to be large enough that it contains at
least one feature, but not so large that it contains multiple features.
Typical values for this parameter are between 15 and 55, with 35
being a good starting point for most users. Noticeable light/dark
(grayscale) contrast is critical for the source template.
Search Region The search region needs to be large enough that the optimal
location for the template is found. In general, no part of the
specimen moves more than the grips or platens, so the motion of
these is a good guideline for how large the template needs to be.
For example, if they move 50 pixels over the 10 frames you are
interested in, it is unlikely that any part of the specimen is moving
more than 5 pixels/frame and so a good value for the search region
parameter would be 11 (5 pixels each way, plus the center pixel).
Use Source
Template From First Image tracks all images against the first in the series (1
→2,
1
→3, 1→4…).
Previous Image tracks each subsequent image against the image
before it (1
→2, 2→3, 3→4…).
First Image Tracking tends to have poorer correlation than Previous
Image Tracking because the current image is usually closer in
content to the previous image than it is to the first image in the
sequence. Previous Image Tracking tends to have good correlation
for each individual step, but is prone to error accumulation since
each step is independent. The best method for a given data set will
depend on the number of images and the content of the images.
Sometimes it is best to use Previous Image Tracking but to only
use every other image or every n
th
image rather than all the images
available. Sometimes it is best to use First Image Tracking and use
every image but set the source image in the middle of the image
series rather than at the beginning.
Set Search
Region Centre New Point Locations The location of the center of the search
region is set to the same location of that point in the previous image
(even when the source template is from the first image).
Existing Point Locations The search region center location is set
to the previously tracked location of that point. When no previously
tracked point exists, the location is chosen in the same way as New
Point Locations.
Use Strain
Based
Deformable
Templates When this option is checked, the source template will be scaled
according to strains calculated from the Size parameters from the
test data. In other words, the source template will be deformed
according to the displacement of the grips or platens at that point in
the test. Best tracking results are often obtained when using this
option. However, this option may not be the best for simple uniaxial
tests or tests where the specimen deformation is non-uniform.
7. Perform tracking with either Track All Points or Track Selected Points .