Chapter 5
Machine Vision
©
National Instruments Corporation
5-5
IMAQ Vision for LabWindows/CVI User Manual
Figure 5-3.
Locating Coordinate System Axes with Two Search Areas
2.
Use the
options
parameter to choose the options you need to locate the
edges on the object, the coordinate system axis direction, and the
results that you want to overlay onto the image. Set the
options
parameter to NULL to use the default options.
3.
Choose the mode for the function. To build a coordinate transform for
the first time, set
mode
to IMAQ_FIND_REFERENCE. To update the
coordinate transform in subsequent images, set this mode to
IMAQ_UPDATE_TRANSFORM.
Using Pattern Matching to Build a Coordinate Transform
You can build a coordinate transform using pattern matching. Use
imaqFindTransformPattern()
to define a coordinate system based on
the location of a reference feature. Use this technique when the object under
inspection does not have straight, distinct edges. Follow the steps below to
build a coordinate reference system using pattern matching:
Note
The object may rotate ±360
°
in the image using this technique if you use
rotation-invariant pattern matching.
1
Primary Search Area
2
Secondary Search Area
3
Origin of the Coordinate System
4
Measurement Area
1
3
2
4
1
3
2
4
a.
b.
