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National Instruments IMAQ Vision for Measurement Studio Analytic Geometry Measurements, Instrument Reader Measurements

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Chapter5 MachineVision

©NationalInstruments Corporation 5-27 IMAQVision for LabWindows/CVI User Manual

Analytic Geometry Measurements

Use the following functions to make geometrical measurements from the

points you detect in the image:

•imaqFitLine()—Fitsa line to a set of points a ndcom putes the

equation of the line.

•imaqFitCircle()—Fitsa circle to a set of at least three points and

computes its area, perimeter and radius.

•imaqFitEllipse()—Fitsan ellipse to a set of at least six points and

computes its area, perimeter,and the l engths of its major and minor

axis.

•imaqGetIntersection()—Findsthe intersection point of two lines

specifiedby their start and end points.

•imaqGetAngle()—Findsthe smaller angle between two lines.

•imaqGetPerpendicularLine()—Findsthe perpen dicular line

froma point to a line and computes the perpendicular distance between

the point and the line.

•imaqGetBisectingLine()—Findsthe li ne that bisects the angle

formed bytwo lin es.

•imaqGetMidLine()—Findsthe line that is m idwaybe tween a point

and a line and is parallel to the line.

•imaqGetPolygonArea()—Calculatesthe area of a polygo n

specifiedby its vertex points.

Instrument Reader Measurements

Youcan make measurements based on the values obtained by meter, LCD,

and barcode readers.

Use imaqGetMeterArc()to calibrate a meter or gauge that you want to

read.The imaqGetMeterArc() function calibrates the meter using one of

twomodes. The IMAQ_METER_ARC_ROI mode uses the initial position and

the full-scale position of the needle. When using this mode, the function

calculatesthe position of the base of the needle and the arc traced by the tip

ofthe needle. The IMAQ_METER_ARC_POINTSmode calibrates the meter

usingthree points on the meter: the b ase of the needle, the tip of the needle

at its initial position, and the tip of the needle at its full-scale position.

When using this mode, the function calculates the position of the points

along the arc coveredby the tip of the needle. Use imaqReadMeter() to

readthe position of the needle using the base of the needle and the array of

points on thearc traced by the tip of the needle.

Contents

Main IMAQ Page Important Information Warranty Copyright Trademarks WARNINGREGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS Conventions Contents Chapter 1 Introduction to IMAQ Vision Chapter 2 Getting Measurement-Ready Images Chapter 3 Grayscale and Color Measurements Chapter 4 Blob Analysis Chapter 5 Machine Vision Page Introduction to IMAQ Vision About IMAQ Vision Documentation and Examples Application Development Environments IMAQ Vision Function Tree Page IMAQ Machine Vision Function Tree Creating IMAQ Vision Applications Chapter1 Introductionto IMAQ Vision Figure1-2. InspectionSteps for Building a Vision Application IMAQVision for LabWindows/CVI User Manual 1-6 ni.com Getting Measurement-Ready Images Set Up Your Imaging System Calibrate Your Imaging System Create an Image Page Source and Destination Images AcquireorReadanImage Acquiring an Image Reading a File Converting an Array to an Image Display an Image Attach Calibration Information Analyze an Image Improve an Image Lookup Tables Filters Convolution Filter Nth Order Filter Grayscale Morphology FFT Page Complex Image Operations Grayscale and Color Measurements Define Regions of Interest Interactively Defining Regions Page Page Page Page Programmatically Defining Regions Defining Regions with Masks Measure Grayscale Statistics Measure Color Statistics Figure3-4. Primary Components of a Color Image Comparing Colors Learning Color Information Choosing the Right Color Information Specifying the Color Information to Learn Using the Entire Image Using a Region in the Image Using Multiple Regions in the Image Choosing a Color Representation Sensitivity Ignoring Learned Colors Blob Analysis Correct Image Distortion Create a Binary Image Improve the Binary Image Removing Unwanted Blobs Separating TouchingBlobs Improving Blob Shapes Make Particle Measurements Page Page Convert Pixel Coordinates to Real-World Coordinates Machine Vision Locate Objects to Inspect UsingEdgeDetectiontoBuildaCoordinateTransform Page Using Pattern Matching to Build a Coordinate Transform Page Chapter5 MachineVision NationalInstruments Corporation 5-7 IMAQVision for LabWindows/CVI User Manual ChoosingaMethodtoBuildtheCoordinateTransform Figure5-4. Buildinga Coordinate Transform Set Search Areas Interactively Defining Regions Programmatically Defining Regions Find Measurement Points Finding Features Using Edge Detection Finding Lines or Circles Figure5-5. Findinga Straight Feature Finding Edge Points Along One Search Contour Finding Edge Points Along Multiple Search Contours Finding Points Using Pattern Matching Defining and Create Good TemplateImages Symmetry Feature detail Positional information Background information Trainingthe Pattern Matching Algorithm Defining a Search Area Setting Matching Parameters and Tolerances Match Mode Minimum Contrast Rotation Angle Ranges Testingthe Search Algorithm on Test Images Using a Ranking Method to Verify Results Finding Points Using Color Pattern Matching Defining and Creating Good Color TemplateImages Color Information Symmetry Feature Detail Positional Information Trainingthe Color Pattern Matching Algorithm Defining a Search Area Setting Matching Parameters and Tolerances Color Sensitivity Search Strategy Color Score Weight Minimum Contrast Rotation Angle Ranges Testingthe Search Algorithm on Test Images Finding Points Using Color Location Convert Pixel Coordinates to Real-World Coordinates Make Measurements Distance Measurements Analytic Geometry Measurements Instrument Reader Measurements Display Results Page Calibration Perspective and Nonlinear Distortion Calibration Defining a Calibration Template Defining a Reference Coordinate System Page Page Learning Calibration Information Specifying Scaling Factors Choosing a Region of Interest Choosing a Learning Algorithm Using the Learning Score Learning the Error Map Learning the Correction Table Setting the Scaling Method Calibration Invalidation Simple Calibration Save Calibration Information Attach Calibration Information A Technical Support Resources Web Support NI Developer Zone Customer Education System Integration Worldwide Support Glossary Numbers/Symbols A B C Page D E F G H I Page J K L M N O P Page Q R S T Page Index A B C D E F G H I Page Page L M N O P R S T V W Z