fit_primitives_object_model_3d — Fit 3D primitives into a set of 3D points.
fit_primitives_object_model_3d( : : ObjectModel3D, GenParamName, GenParamValue : ObjectModel3DOut)
The operator fit_primitives_object_model_3d fits a 3D primitive,
i.e., a simple 3D shape, into a set of 3D points given by a 3D object
model with the handle ObjectModel3D. The shapes that are
available as 3D primitives comprise a cylinder, a sphere, and a plane.
As the operator does not perform a segmentation of the set of 3D points
that is contained in the input 3D object model, you have to make sure
that the contained 3D points already correspond to a 3D primitive.
A segmentation can be performed, e.g., with the
operator segment_object_model_3d.
fit_primitives_object_model_3d returns the handle
ObjectModel3DOut for the output 3D object model, which
contains information that concern, e.g., the type and parameters
of the fitted 3D primitive.
This information can be queried from the 3D object model with
get_object_model_3d_params. Note that the extent of primitives
of the type plane and cylinder can be queried with
get_object_model_3d_params, as well.
The parameters of a cylinder are the (x-, y-, z-)coordinates
of the center, the normed (x-, y-, z-)directions
of the main axis of the cylinder, and the radius of the cylinder. The
center does not necessarily lie in the center of gravity of the
cylinder (see the explanation of the parameters MinExtent and
MaxExtent of the operator gen_cylinder_object_model_3d).
The sign of the main axis is determined such that the main axis points
towards the half space in which the origin is located.
For a sphere the parameters are the (x-, y-, z-)coordinates of the
center and the radius of the sphere.
A plane is given by the 4 parameters of the hessian normal form,
i.e., the unit normal (x-, y-, z-) vector and the orthogonal
distance of the plane from the origin of the coordinate system.
The sign of the hessian normal form is determined such that the normal
vector points towards the side of the plane on which the origin is located
and the distance is not positive.
If no primitive can be fitted to the set of 3D points, the returned object
model will not contain a primitive. However, depending on the parameter
values for 'output_point_coord' and 'output_xyz_mapping'
(see below), the returned object model is either empty, or contains
the 3D points, or contains the 3D points and the mapping from the 3D
points to image coordinates of the input object model
ObjectModel3D.
To control the fitting, you can adjust some
generic parameters within GenParamName and GenParamValue.
But note that for a lot of applications the default
values are sufficient and no adjustment is necessary.
The following values for GenParamName and GenParamValue
are possible:
The parameter specifies which type of 3D primitive should be fitted into the set of 3D points. You can specify a specific primitive type by setting 'primitive_type' to 'cylinder', 'sphere', or 'plane'. Then, only the selected type of 3D primitive is fitted into the set of 3D points. You can also specify a set of specific 3D primitives that should be fitted by setting 'primitive_type' to a tuple consisting of different primitive types. If all types of 3D primitives should be fitted, you can set 'primitive_type' to 'all'. Note that if more than one primitive type is selected, only the best fitting 3D primitive, i.e., the 3D primitive with the smallest quadratic residual error, is returned.
List of values: 'cylinder', 'sphere', 'plane', 'all'
Default value: 'cylinder'
The parameter specifies the used algorithm for the fitting of the 3D primitive. When fitting a plane, the results are identical for the different algorithms. If 'fitting_algorithm' is set to 'least_squares', the approach minimizes the quadratic distance between the 3D points and the resulting primitive. If 'fitting_algorithm' is set to 'least_squares_huber', the approach is similar to 'least_squares', but the points are weighted to decrease the impact of outliers based on the approach of Huber (see below). If 'fitting_algorithm' is set to 'least_squares_tukey', the approach is also similar to 'least_squares', but the points are weighted and outliers are ignored based on the approach of Tukey (see below).
For 'least_squares_huber' and 'least_squares_tukey' a robust error statistics is used to estimate the standard deviation of the distances from the object points without outliers from the fitting primitive. The Tukey algorithm removes outliers, whereas the Huber algorithm only damps them, or more precisely, weights them linearly. In practice, the approach of Tukey is recommended.
List of values: 'least_squares', 'least_squares_huber', 'least_squares_tukey'
Default value: 'least_squares'
The parameter specifies the minimum radius of a cylinder or a sphere. If a cylinder or a sphere with a smaller radius is fitted, the resulting 3D object model is empty. The parameter is ignored when fitting a plane. The unit is meter.
Suggested values: 0.01, 0.02, 0.1
Default value: 0.01
The parameter specifies the maximum radius of a cylinder or a sphere. If a cylinder or a sphere with a larger radius is fitted, the resulting 3D object model is empty. The parameter is ignored when fitting a plane. The unit is meter.
Suggested values: 0.02, 0.04, 0.2
Default value: 0.2
The parameter determines if the 3D points used for the fitting are copied to the output 3D object model. If 'copy_point_coord' is set to 'true', the 3D points are copied. If 'copy_point_coord' is set to 'false', no 3D points are copied.
List of values: 'true','false'
Default value: 'true'
The parameter determines
if a mapping from the 3D points to image coordinates is
copied to the output 3D object model. This information is
needed, e.g., when using the operator object_model_3d_to_xyz
after the fitting (e.g., for a visualization). If
'output_xyz_mapping' is set to 'true',
the image coordinate mapping is copied. Note that the parameter is
only valid, if the image coordinate mapping is available in the input
3D object model. Make sure that, if you derive the input 3D object
model by copying it with the operator copy_object_model_3d
from a 3D object model that contains such a mapping, the mapping is
copied, too. Furthermore, the parameter is only valid, if
the 3D points are copied to the output 3D object model, which is set
with the parameter 'output_point_coord'.
List of values: 'true','false'
Default value: 'false'
The minimum number of 3D points that are necessary to fit a plane is three. The minimum number of 3D points that is necessary to fit a sphere is four. The minimum number of 3D points that is necessary to fit a cylinder is five.
ObjectModel3D (input_control) object_model_3d(-array) → (handle)
Handle of the input 3D object model.
GenParamName (input_control) attribute.name-array → (string)
Names of the generic parameters.
Number of elements: GenParamName == GenParamValue
List of values: 'fitting_algorithm', 'max_radius', 'min_radius', 'output_point_coord', 'output_xyz_mapping', 'primitive_type'
GenParamValue (input_control) attribute.name-array → (string / real / integer)
Values of the generic parameters.
Number of elements: GenParamValue == GenParamName
Suggested values: 'cylinder', 'sphere', 'plane', 'all', 'least_squares', 'least_squares_huber', 'least_squares_tukey', 0.01, 0.05, 0.1, 0.2, 'true', 'false'
ObjectModel3DOut (output_control) object_model_3d(-array) → (handle)
Handle of the output 3D object model.
fit_primitives_object_model_3d returns 2 (H_MSG_TRUE) if all parameter
values are correct. If necessary, an exception is raised.
xyz_to_object_model_3d,
read_object_model_3d
get_object_model_3d_params,
object_model_3d_to_xyz,
write_object_model_3d,
clear_object_model_3d
3D Metrology