National Instruments IMAQTM - Manual (Page 80)

Chapter 5 Performing Machine Vision Tasks
IMAQ Vision for Visual Basic User Manual 5-28 ni.com
• FindMidLine —Finds the line that is midway between a point and a
line and is parallel to the line.
• FindPolygonArea —Calculates the area of a polygon specified by its
vertex points.
Instrument Reader Measurements
You can make measurements based on the values obtained by meter, LCD,
and barcode readers.
Use CWIMAQMeterArc.CreateFromPoints or
CWIMAQMeterArc.CreateFromLines to calibrate a meter or
gauge that you want to read. CWIMAQMeterArc.CreateFromLines
calibrates the meter using the initial position and the full-scale position
of the needle.
CWIMAQMeterArc.CreateFromPoints calibrates the
meter using three points on the meter: the base of the needle, the tip of
the needle at its initial position, and the tip of the needle at its full-scale
position. Use
CWIMAQVision.ReadMeter to read the position of the
needle using the CWIMAQMeterArc object.
Use CWIMAQVision.FindLCDSegments to calculate the regions of
interest around each digit in an LCD or LED. To find the area of each
digit, all the segments of the indicator must be activated. Use
CWIMAQVision.ReadLCD to read the digits of an LCD or LED.
Identify Parts Under Inspection
In addition to making measurements after you set regions of inspection,
you also can identify parts using classification, OCR, and barcode reading.
Classifying Samples
Use classification to identify an unknown object by comparing a set of its
significant features to a set of features that conceptually represent classes
of known objects. Typical applications involving classification include the
following:
• Sorting—Sorts objects of varied shapes. For example, sorting different
mechanical parts on a conveyor belt into different bins.
• Inspection—Inspects objects by assigning each object an identification
score and then rejecting objects that do not closely match members of
the training set.