GE Mentor Visual iQ User Manual page 47

About the Matching Cursors
For each cursor you place on the left image during stereo measurement, the system
places a matching cursor on the right image for use in triangulation.
You must place each left cursor on an image point (a pixel) that has sufficient
surrounding detail to differentiate it from its neighboring pixels. If the neighboring
pixels look the same as the point you choose — especially the pixels to the point's left
and right, for example, pixels along a smooth horizontal line — the system cannot
accurately place the matching cursor. When there is enough differentiating detail,
the "match strength" is high (meaning that the generated match point clearly
matches better than its neighboring pixels — the system's confidence in the match
is high). But if there is not enough detail, the match strength is low (meaning that the
generated point and its neighboring pixels match almost equally well — the match
may be correct, but the system's confidence in the match is low).
For every matching cursor, the system calculates a match strength value between
<0> (lowest confidence) and <5> (highest confidence). If too little detail is present,
the system simply does not generate a matching cursor. Whenever possible, try
to achieve a match strength of at least <3>. If you cannot achieve this level, try
capturing another image with less glare or more image details. (Adjust the tip
orientation or image brightness.)
Even when match strength is <5>, and especially when the match strength is
lower, you need to verify that the matching cursor appears to be placed properly. A
matching cursor that is off by just one pixel can significantly impact measurement
accuracy.
Repositioning a Matching Cursor
Note: Misplaced matching cursors most likely occur when the measurement area
contains a repeating pattern. Generally, the best results are achieved by leaving
the matching cursors exactly where the system places them.
Move the matching cursor to the correct position.
When you stop moving the cursor, the system optimizes the match position. Each
manually corrected matching cursor is indicated by the absence of a match strength
number.
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07/30/2014