Make Measurements

You can make different types of measurements either directly from the image or from points that you detect in the image.

Making Distance Measurements

Use Measure Distances VIs to measure the separation between two edges in a rectangular search region. Specify the parameters for edge detection and the separation between the search lines that you want to use within the search region to find the edges.

Note  Use the IMAQ Select Rectangle VI to generate a valid input search region for the clamp VIs.

First the VIs use the rake function to detect points along two edges of the object under inspection. Then the VIs compute the distance between the points detected on the edges along each search line of the rake. The VIs return the largest or smallest distance in either the horizontal or vertical direction, and they output the coordinates of all the edge points that they find.

The following list describes the available clamp VIs:

• IMAQ Clamp Horizontal Max—Measures the largest horizontal separation between two edges in a rectangular search region.
• IMAQ Clamp Horizontal Min—Finds the smallest horizontal separation between two vertically oriented edges.
• IMAQ Clamp Vertical Max—Finds the largest vertical separation between two horizontally oriented edges.
• IMAQ Clamp Vertical Min—Finds the smallest vertical separation between two horizontally oriented edges.

Use the IMAQ Point Distances VI to compute the distances between consecutive pairs of points in an array of points. You can obtain these points from the image using any one of the feature detection methods described in Find Measurement Points.

Making Analytic Geometry Measurements

Use the following VIs to make geometrical measurements from the points you detect in the image:

• IMAQ Fit Line—Fits a line to a set of points and computes the equation of the line.
• IMAQ Fit Circle 2—Fits a circle to a set of at least three points and computes its area, perimeter and radius.
• IMAQ Fit Ellipse 2—Fits an ellipse to a set of at least six points and computes its area, perimeter, and the lengths of its major and minor axis.
• IMAQ Lines Intersection—Finds the angle and point of intersection of two lines specified by their start and end points.
• IMAQ Perpendicular Line—Finds the perpendicular line and distance from a point to a line.
• IMAQ Bisecting Line—Finds the line that bisects the angle formed by two lines.
• IMAQ Mid Line—Finds the line that is midway between a point and a line and is parallel to the line.
• IMAQ Polygon Area—Calculates the area of a polygon specified by its vertex points.

Making Instrument Reader Measurements

Use the following VIs to make measurements based on the values obtained by meter and LCD readers:

• Use the IMAQ Get Meter or IMAQ Get Meter 2 VIs to calibrate a meter or gauge that you want to read.

• IMAQ Get Meter calibrates the meter using the initial position and full-scale position of the needle. This VI calculates the position of the base of the needle and the arc traced by the tip of the needle.
• IMAQ Get Meter 2 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. This VI calculates the position of the points along the arc covered by the tip of the needle.

• Use the IMAQ Read Meter VI to read the position of the needle using the base of the needle and the array of points on the arc traced by the tip of the needle.
• Use the IMAQ Get LCD ROI VI to calculate the ROI 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 the IMAQ Read Single Digit VI to read one digit of an LCD or LED. Use the IMAQ Read LCD VI to read multiple digits of an LCD or LED.