find_shape_model_3d — Find the best matches of a 3D shape model in an image.
find_shape_model_3d(Image : : ShapeModel3DID, MinScore, Greediness, NumLevels, GenParamName, GenParamValue : Pose, CovPose, Score)
The operator find_shape_model_3d finds the best matches of
the 3D shape model ShapeModel3DID in the input
Image. The 3D shape model must have been created
previously by calling create_shape_model_3d or
read_shape_model_3d.
The 3D pose of the found instances of the model is returned in
Pose. The pose is in the form
, where
ccs denotes the camera coordinate system and
mcs the model coordinate system (which is a 3D world coordinate
system), see Transformations / Poses and
“Solution Guide III-C - 3D Vision”.
Hence, it describes the pose of the 3D object model in camera coordinates.
It should be noted that the resulting
Pose does not refer to reference coordinate system that is
introduced in create_shape_model_3d but to the original 3D
object model coordinate system used in the CAD file. If a pose
refinement was applied (see below), additionally the accuracy of the
six pose parameters are returned in CovPose. By default,
CovPose contains the 6 standard deviations of the pose
parameters for each match. In contrast, if the generic parameter
'cov_pose_mode' (see below) was set to
'covariances', CovPose contains the 36 values of
the complete 6×6 covariance matrix of the 6
pose parameters. Note that this reflects only an inner accuracy from
which the real accuracy of the pose may differ. Finally, the score
of each found instance is returned in Score. The score is
a number between 0 and 1, which is an approximate measure of how
much of the model is visible in the image. If, for example, half of
the model is occluded, the score cannot exceed 0.5.
The domain of the image Image determines the search space
for the reference point of the 3D object model.
The parameter MinScore determines what score a potential
match must at least have to be regarded as an instance of the model
in the image. The larger MinScore is chosen, the faster
the search is. If the model can be expected never to be occluded in
the images, MinScore may be set as high as 0.8 or even 0.9.
Note that in images with a high degree of clutter or strong
background texture, MinScore should be set to a value not
much lower than 0.7 since otherwise false matches could
be found.
The parameter Greediness determines how “greedily” the
search should be carried out. If Greediness=0, a safe
search heuristic is used, which always finds the model if it is
visible in the image. However, the search will be relatively time
consuming in this case. If Greediness=1, an unsafe
search heuristic is used, which may cause the model not to be found
in rare cases, even though it is visible in the image. For
Greediness=1, the maximum search speed is achieved. In
almost all cases, the 3D shape model will always be found for
Greediness=0.9.
The number of pyramid levels used during the search is determined
with NumLevels. If necessary, the number of levels is
clipped to the range given when the 3D shape model was created with
create_shape_model_3d. If NumLevels is set to
0, the number of pyramid levels specified in
create_shape_model_3d is used. Optionally,
NumLevels can contain a second value that determines the
lowest pyramid level to which the found matches are tracked. Hence,
a value of [4,2] for NumLevels means that the
matching starts at the fourth pyramid level and tracks the matches
to the second lowest pyramid level (the lowest pyramid level is
denoted by a value of 1). This mechanism can be used to decrease
the runtime of the matching. If the lowest pyramid level to use is
chosen too large, it may happen that the desired accuracy cannot be
achieved, or that wrong instances of the model are found because the
model is not specific enough on the higher pyramid levels to
facilitate a reliable selection of the correct instance of the
model. In this case, the lowest pyramid level to use must be set to
a smaller value.
In addition to the parameters described above, there are some
generic parameters that can optionally be used to influence the
matching. For most applications these parameters need not to be
specified but can be left at their default values. If desired, these
parameters and their corresponding values can be specified by using
GenParamName and GenParamValue, respectively.
The following values for GenParamName are possible:
If the pose range in which the model is to be searched is smaller
than the pose range that was specified during the model creation
with create_shape_model_3d, the pose range can be
restricted appropriately with the following parameters. If the
values lie outside the pose range of the model, the values are
automatically clipped to the pose range of the model.
Sets the minimum longitude of the pose range.
Suggested values: 'rad(-45)', 'rad(-30)', 'rad(-15)'
Default value: 'rad(-180)'
Sets the maximum longitude of the pose range.
Suggested values: 'rad(15)', 'rad(30)', 'rad(45)'
Default value: 'rad(180)'
Sets the minimum latitude of the pose range.
Suggested values: 'rad(-45)', 'rad(-30)', 'rad(-15)'
Default value: 'rad(-90)'
Sets the maximum latitude of the pose range.
Suggested values: 'rad(15)', 'rad(30)', 'rad(45)'
Default value: 'rad(90)'
Sets the minimum camera roll angle of the pose range.
Suggested values: 'rad(-45)', 'rad(-30)', 'rad(-15)'
Default value: 'rad(-180)'
Sets the maximum camera roll angle of the pose range.
Suggested values: 'rad(15)', 'rad(30)', 'rad(45)'
Default value: 'rad(180)'
Sets the minimum camera-object-distance of the pose range.
Suggested values: 0.05, 0.1, 0.5, 1.0
Default value: 0
Sets the maximum camera-object-distance of the pose range.
Suggested values: 0.05, 0.1, 0.5, 1.0
Default value:
Further generic parameters that do not concern the pose range can be specified:
With this parameter the maximum number of instances to be found
can be determined. If more than the specified number of
instances with a score greater than MinScore are found
in the image, only the best 'num_matches' instances are
returned. If fewer than 'num_matches' are found, only
that number is returned, i.e., the parameter MinScore
takes precedence over 'num_matches'. If
'num_matches' is set to 0, all matches that
satisfy the score criterion are returned. Note that the more
matches should be found the slower the matching will be.
Suggested values: 0, 1, 2, 3
Default value: 1
It may happen that multiple instances with similar positions but
with different orientations are found in the image. The
parameter 'max_overlap' determines by what fraction
(i.e., a number between 0 and 1) two instances may at most
overlap in order to consider them as different instances, and
hence to be returned separately. If two instances overlap each
other by more than the specified value only the best instance is
returned. The calculation of the overlap is based on the
smallest enclosing rectangle of arbitrary orientation (see
smallest_rectangle2) of the found instances.
If in create_shape_model_3d for
'lowest_model_level' a value larger than 1
was passed, the overlap calculation is based on the projection
of the smallest enclosing axis-parallel cuboid of the 3D
object model. Because in this case the overlap might be
overestimated, in some cases it could be necessary to increase
the value for 'max_overlap'. If
'max_overlap'=0, the found instances may not overlap
at all, while for 'max_overlap'=1 all instances are
returned.
Suggested values: 0.0, 0.2, 0.4, 0.6, 0.8, 1.0
Default value: 0.5
This parameter
determines whether the poses of the instances should be refined
after the matching. If 'pose_refinement' is set to
'none' the model's pose is only determined with a
limited accuracy. In this case, the accuracy depends on several
sampling steps that are used inside the matching process and,
therefore cannot be predicted very well. Therefore,
'pose_refinement' should only be set to 'none'
when the computation time is of primary concern and an
approximate pose is sufficient. In all other cases the pose
should be determined through a least-squares adjustment, i.e.,
by minimizing the distances of the model points to their
corresponding image points. In order to achieve a high
accuracy, this refinement is directly performed in
3D. Therefore, the refinement requires additional computation
time. If the system variable (see set_system)
'opengl_hidden_surface_removal_enable' is set to
'true' (which is default if it is available) and the model
ShapeModel3DID was created with
'fast_pose_refinement' set to 'false', the
projection of the model in the pose refinement step is accelerated
using the graphics card. Depending on the graphics card this is
significantly faster than the non accelerated algorithm. Be aware that
the results of the OpenGL projection are slightly different
compared to the analytic projection.
The different modes for least-squares adjustment
('least_squares', 'least_squares_high', and
'least_squares_very_high') can be used to determine the
accuracy with which the minimum distance is searched for. The
higher the accuracy is chosen, the longer the pose refinement
will take, however. For most applications
'least_squares_high' should be chosen because this
results in the best trade-off between runtime and accuracy. Note
that the pose refinement can be sped up by passing
'fast_pose_refinement' for the parameter
GenParamName of the operator
create_shape_model_3d.
List of values: 'none', 'least_squares', 'least_squares_high', 'least_squares_very_high'
Default value: 'least_squares_high'
This parameter determines
whether the score of the matches is recomputed after the pose
refinement. If 'recompute_score' is set to
'false', the score is returned that was computed before
the pose refinement. In some cases, however, the pose
refinement changes the object pose by more than one pixel in the
image. Consequently, the original score does not appropriately
describe the refined match any longer. This could result in
wrong matches obtaining high scores or perfect matches obtaining
low scores. To obtain a more meaningful score that reflects the
pose changes due to the pose refinement, the score can be
recomputed after the pose refinement by setting
'recompute_score' to 'true'. Note that this
might change the order of the matches as well as the selection
of matches that is returned. Also note that the recomputation
of the score values needs additional computation time. This
increase of the run-time can be reduced by setting the generic
parameter 'fast_pose_refinement' of the operator
create_shape_model_3d to 'true'.
List of values: 'false', 'true'
Default value: 'false'
This parameter only takes effect if 'pose_refinement' is set to a value other than 'none', and hence, a least-squares adjustment is performed. Then, in some cases it might be useful to apply a robust outlier suppression during the least-squares adjustment. This might be necessary, for example, if a high degree of clutter is present in the image, which prevents the least-squares adjustment from finding the optimum pose. In this case, 'outlier_suppression' should be set to either 'medium' (eliminates a medium proportion of outliers) or 'high' (eliminates a high proportion of outliers). However, in most applications, no robust outlier suppression is necessary, and hence, 'pose_refinement' can be set to 'none'. It should be noted that activating the outlier suppression comes along with a significantly increasing computation time.
List of values: 'none', 'medium', 'high'
Default value: 'none'
This parameter only
takes effect if 'pose_refinement' is set to a value
other than 'none', and hence, a least-squares
adjustment is performed. 'cov_pose_mode' determines the
mode in which the accuracies that are computed during the
least-squares adjustment are returned in CovPose. If
'cov_pose_mode' is set to
'standard_deviations', the 6 standard deviations of the
6 pose parameters are returned for each match. In contrast, if
'cov_pose_mode' is set to 'covariances',
CovPose contains the 36 values of the complete 6×6
covariance matrix of the 6 pose parameters.
List of values: 'standard_deviations', 'covariances'
Default value: 'standard_deviations'
The model is searched within those points of the domain of the
image in which the model lies completely within the image.
This means that the model will not be found if it extends beyond
the borders of the image, even if it would achieve a score
greater than MinScore. Note that, if for a certain pyramid
level the model touches the image border, it might not be found
even if it lies completely within the original image.
As a rule of thumb, the model might not be found if its distance to
an image border falls below .
This behavior can be changed by setting 'border_model' to
'true', which will
cause models that extend beyond the image border to be found if
they achieve a score greater than MinScore. Here,
points lying outside the image are regarded as being occluded,
i.e., they lower the score. It should be noted that the runtime
of the search will increase in this mode. Note further, that in
rare cases, which occur typically only for artificial images, the
model might not be found also if for certain pyramid levels the
model touches the border of the reduced domain. Then, it may help
to enlarge the reduced domain by
using, e.g.,
dilation_circle.
List of values: 'false', 'true'
Default value: 'false'
Image (input_object) (multichannel-)image → object (byte / uint2)
Input image in which the model should be found.
ShapeModel3DID (input_control) shape_model_3d → (handle)
Handle of the 3D shape model.
MinScore (input_control) real → (real)
Minimum score of the instances of the model to be found.
Default value: 0.7
Suggested values: 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0
Typical range of values: 0
≤
MinScore
≤
1
Minimum increment: 0.01
Recommended increment: 0.05
Greediness (input_control) real → (real)
“Greediness” of the search heuristic (0: safe but slow; 1: fast but matches may be missed).
Default value: 0.9
Suggested values: 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0
Typical range of values: 0
≤
Greediness
≤
1
Minimum increment: 0.01
Recommended increment: 0.05
NumLevels (input_control) integer-array → (integer)
Number of pyramid levels used in the matching
(and lowest pyramid level to use if
|NumLevels| = 2).
Default value: 0
List of values: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
GenParamName (input_control) attribute.name-array → (string)
Names of (optional) parameters for controlling the behavior of the operator.
Default value: []
List of values: 'border_model', 'cam_roll_max', 'cam_roll_min', 'cov_pose_mode', 'dist_max', 'dist_min', 'latitude_max', 'latitude_min', 'longitude_max', 'longitude_min', 'max_overlap', 'num_matches', 'outlier_suppression', 'pose_refinement', 'recompute_score'
GenParamValue (input_control) attribute.name-array → (integer / real / string)
Values of the optional generic parameters.
Default value: []
Suggested values: -0.78, -0.35, -0.17, 0.0, 0.17, 0.35, 0.78, 0.1, 0.2, 0.5, 'none', 'false', 'true', 'least_squares', 'least_squares_high', 'least_squares_very_high', 'standard_deviations', 'covariances', 'medium', 'high'
Pose (output_control) pose(-array) → (real / integer)
3D pose of the 3D shape model.
CovPose (output_control) real-array → (real)
6 standard deviations or 36 covariances of the pose parameters.
Score (output_control) real-array → (real)
Score of the found instances of the 3D shape model.
read_object_model_3d (DXFModelFileName, 'm', [], [], ObjectModel3D, \
DxfStatus)
CamParam := ['area_scan_division',0.01221,2791,7.3958e-6,7.4e-6,\
308.21,245.92,640,480]
create_shape_model_3d (ObjectModel3D, CamParam, 0, 0, 0, 'gba', \
-rad(20), rad(20), -rad(20), rad(20), 0, \
rad(360), 0.15, 0.2, 10, [], [], ShapeModel3DID)
grab_image_async (Image, AcqHandle, -1)
find_shape_model_3d (Image, ShapeModel3DID, 0.6, 0.9, 0, [], [], \
Pose, CovPose, Score)
project_shape_model_3d (ModelContours, ShapeModel3DID, CamParam, \
Pose, 'true', rad(30))
If the parameter values are correct, the operator
find_shape_model_3d returns the value TRUE. If the input is
empty (no input images are available) the behavior can be set via
set_system('no_object_result',<Result>). If necessary, an
exception is raised. If the model was created with
find_shape_model_3d by setting 'metric' to
'ignore_part_polarity' and a multi-channel input image is
passed in Image, the error 3359 is raised.
create_shape_model_3d,
read_shape_model_3d
convert_point_3d_cart_to_spher,
convert_point_3d_spher_to_cart,
create_cam_pose_look_at_point,
trans_pose_shape_model_3d
3D Metrology