| Operators |
create_metrology_model — Create the data structure that is needed to measure geometric shapes.
create_metrology_model( : : : MetrologyHandle)
create_metrology_model creates a metrology model, i.e., the data structure that is needed to measure objects with a specific geometric shape (metrology object) via 2D metrology, and returns it in the handle MetrologyHandle.
Basic principle of 2D metrology
Generally, for 2D metrology approximate values for the positions, orientations and geometric shapes of the objects to measure must be provided. Within the image that shows the objects, the boundaries of these approximate objects are used to locate the real edges of the objects to adapt the parameters of the geometric shapes so that they fit optimally to the image data. The results of the measurements are the optimized parameters. The metrology model is used to store all necessary information like the initial parameters for the positions and geometric shapes of the metrology objects, parameters that control the measurement, and the results of the measurements. The geometric shapes that can be measured via 2D metrology comprise circles, ellipses, rectangles, and lines.
The edges of the object in the image are located within so-called measure regions. These are rectangular regions that the major axis are arranged perpendicular to the boundaries of the approximate objects so that their centers lie on the boundary. Parameters that adjust the dimension and distribution of the measure regions are specified together with the approximate shape parameters for each object. The measure direction for the detection of the edges within each measure region is from the inside to the outside of the object for objects of type circle, ellipse, and rectangle, and from left to right for objects of type line (seen from the line's start point to its end point). The edges are located internally using the operator measure_pos or fuzzy_measure_pos. The latter uses fuzzy methods and is used only if at least one fuzzy function was set via set_metrology_object_fuzzy_param before applying the measurement. The fitting of the geometric shape to the found edge positions is performed using a RANSAC algorithm.
In the following, the individual steps needed for such a measurement are described:
Providing approximate values
For an efficient measurement, after creating the metrology model with create_metrology_model, the image size for the image in which the measurements will be performed should be specified with set_metrology_model_image_size. Then, metrology objects are added to the metrology model. Each metrology object consists of the approximate shape parameters for the corresponding object in the image and of the parameters that control the measurement. The metrology objects are specified with the operator add_metrology_object_circle_measure for metrology objects of type circle, add_metrology_object_ellipse_measure for metrology objects of type ellipse, add_metrology_object_rectangle2_measure for metrology objects of type rectangle, and add_metrology_object_line_measure for metrology objects of type line. The parameters that control the measurement comprise, e.g., parameters that specify the half lengths of the measure regions and the distance between them. To visually inspect the measure regions, you can access the XLD contours of their boundaries with the operator get_metrology_object_measures. Furthermore, several generic parameters can be adjusted for each metrology object.
Modifying parameters
Many parameters can be set when adding the metrology objects to the metrology model. Some of them can also be modified afterwards using the operator set_metrology_object_param. For example, if a camera calibration has been performed, the camera parameters and the pose of the world coordinate system (WCS) can be added to the metrology objects using set_metrology_object_param. Then, the result of the measurements will be returned in world coordinates. Additionally, the metrology model or metrology objects can be copied with copy_metrology_model or copy_metrology_object, respectively. For an alignment, the metrology objects can be transformed using transform_metrology_object. To write a metrology model to file, the operator write_metrology_model is available. The model can be read from file again using read_metrology_model. The indices of the metrology objects can be queried with get_metrology_object_indices.
Applying the measurement
If all metrology objects were added to the metrology model and all parameters are finally set, the measurement in the image is applied with apply_metrology_model. The operator locates the edges within the measure regions and fits the specified geometric shape to the edge positions using a RANSAC algorithm. If more than one instance of the returned object shape is needed, the generic parameter 'num_instances' must be set to the number of instances that should be returned. The parameter can be set when adding the individual metrology objects or afterwards with the operator set_metrology_object_param.
Accessing the results
After the measurement, the results can be accessed. The adapted geometric shapes of the objects are queried with the operator get_metrology_object_result. Note that if more than one instance of an object is returned, the sequence of the returned instances is arbitrary, i.e., it is no measure for the quality of the fitting. The row and column coordinates of the located edges can be accessed with get_metrology_object_measures. When the metrology model is not needed anymore, it should be destroyed with clear_metrology_model.
Note, that after calling the operator create_metrology_model the operator set_metrology_model_image_size should be called for efficiency reasons.
A metrology model 'MetrologyHandle' cannot be shared between two or more user's threads. Different metrology models can be used independently and safely in different threads.
Handle of the metrology model.
read_image (Image, 'fabrik')
create_metrology_model (MetrologyHandle)
get_image_size (Image, Width, Height)
set_metrology_model_image_size (MetrologyHandle, Width, Height)
add_metrology_object_rectangle2_measure (MetrologyHandle, 270, 230, 0, 30, \
25, 10, 2, 1, 30, [], [], Index)
apply_metrology_model (Image, MetrologyHandle)
get_metrology_object_result (MetrologyHandle, Index, 'all', 'result_type', \
'param', Rectangle)
gen_rectangle2_contour_xld (ContRect, Rectangle[0], Rectangle[1], \
Rectangle[2], Rectangle[3], Rectangle[4])
clear_metrology_model (MetrologyHandle)
If the parameters are valid, the operator create_metrology_model returns the value 2 (H_MSG_TRUE). If necessary, an exception is raised.
set_metrology_model_image_size
2D Metrology
| Operators |