Operator Reference
create_sheet_of_light_model (Operator)
create_sheet_of_light_model — Create a model to perform 3D-measurements using the sheet-of-light
technique.
Signature
create_sheet_of_light_model(ProfileRegion : : GenParamName, GenParamValue : SheetOfLightModelID)
Description
The operator create_sheet_of_light_model creates a model to
perform 3D-Measurements using the sheet-of-light technique.
The sheet-of-light technique performs a three-dimensional reconstruction of the surface of an opaque and diffuse reflecting solid by using an area scan camera and a light line projector (typically a laser line projector). The camera and the line projector must be mounted so that their main axis form an angle of triangulation. The value of the angle of triangulation is typically chosen between 30° and 60°. The projected light line defines a plane in space. This plane intersects the surface of the solid under measurement and builds a profile of the surface visible for the camera. By moving the solid in front of the measurement system (i.e., the combination of the camera and the line projector), it is possible to record the whole surface of the solid. As an alternative, the measurement system can also be moved over the surface under measurement. Please note that the profiles must be oriented roughly horizontal in the profile images, because they are processed column by column.
If geometrical information about the measurement setup is available, it
is possible to compute true three-dimensional coordinates of the
reconstructed surface. For an overview of the required geometrical (i.e.,
calibration) information, refer to the operator
set_sheet_of_light_param. If such information is not available,
the result of the measurement is a disparity image, where each pixel holds
a record of the subpixel precise position of the detected profile.
The operator returns a handle to the sheet-of-light model in
SheetOfLightModelID, which is used for all further operations on
the sheet-of-light model, like modifying parameters of the model, measuring
profiles, applying calibration transformations or accessing the results of
measurements.
Mandatory input iconic parameters
In order to perform measurements, you will have to set the following input iconic parameter:
ProfileRegion:-
defines the region of the profile images, which will be processed by the operator
measure_profile_sheet_of_light. This region should be rectangular and can be generated e.g., by using the operatorgen_rectangle1. If the region passed toProfileRegionis not rectangular, its smallest enclosing rectangle (bounding box) will be used. Note thatProfileRegionis only taken into account by the operatormeasure_profile_sheet_of_lightand is ignored when disparity images are processed.
Default settings of the sheet-of-light model parameters
The default settings of the sheet-of-light model were chosen to perform
non-calibrated measurements in a basic configuration. The following
list provides an overview of the parameter values used by default
(refer to set_sheet_of_light_param for a detailed description
of all supported generic parameters):
- 'method'
-
is set to 'center_of_gravity'
- 'min_gray':
-
is set to 100
- 'num_profiles'
-
is set to 512
- 'ambiguity_solving'
-
is set to 'first'
- 'score_type'
-
is set to 'none'
- 'calibration'
-
is set to 'none'
Modify the sheet-of-light model parameters
We recommend to adapt the default parameters to your specific measurement task, in order to enhance the quality of the measurement or to shorten the runtime. You will also have to modify the default values of the model parameters if you need calibrated results.
create_sheet_of_light_model provides the generic parameters
GenParamName and GenParamValue to modify the default
value of most of the model parameters. Note that model parameters can also
be set by using the operator set_sheet_of_light_param. Nevertheless,
with this second operator only one parameter can be set at the same time,
whereas it is possible to set more than one parameter at the time with
create_sheet_of_light_model. Refer to
set_sheet_of_light_param for a detailed description of all
supported generic parameters.
Please note that the following model parameters can not be set with the
operator create_sheet_of_light_model, and thus have to be set with
the operator set_sheet_of_light_param: 'camera_parameter',
'camera_pose', 'lightplane_pose', and
'movement_pose'.
It is possible to query the value of the model parameters with the
operator get_sheet_of_light_param. The names of all supported
model parameters are returned by the operator
query_sheet_of_light_params.
Use the simplified sheet-of-light model parameters
In case of a simple setup or if not a real metric calibration is necessary, the transformation of the observed disparities into 3D values can be controlled using a simplified parameter set of the sheet-of-light model:
By setting the calibration with the set_sheet_of_light_param to
'offset_scale', the poses and camera parameter are changed to such
values, that an offset of one pixel corresponds to one unit in the 3D
result. This allows to create a 3D object model and 3D images from
an uncalibrated sheet-of-light model.
The transformation from disparity to 3D coordinates can be controlled by
six parameters:
'scale_x', 'scale_y', 'scale_z', 'offset_x',
'offset_y', 'offset_z'. Refer to
set_sheet_of_light_param for a detailed description of all
supported generic parameters.
Use of a handle in multiple threads
Please note that you have to take special care when using a handle of
a sheet-of-light-model SheetOfLightModelID in multiple threads.
One and the same handle cannot be used concurrently in different threads
if they modify the handle. Thus, you have to be careful especially
if the threads call operators that change the data of the handle.
You can find an according hint in the 'Attention' section of the
operators.
Anyway, if you still want to use the same handle in operators that
concurrently write into the handle in different threads you have to
synchronize the threads to assure that they do not access the same
handle simultaneously. If you are not sure if the usage of the same
handle is thread-safe, please see the 'Attention' section of the
respective reference manual entry if it contains a warning pointing
to this problem. However, different handles can be used independently
and safely in different threads.
Execution Information
- Multithreading type: reentrant (runs in parallel with non-exclusive operators).
- Multithreading scope: global (may be called from any thread).
- Processed without parallelization.
This operator returns a handle. Note that the state of an instance of this handle type may be changed by specific operators even though the handle is used as an input parameter by those operators.
Parameters
ProfileRegion (input_object) region → object
Region of the images containing the profiles to be processed. If the provided region is not rectangular, its smallest enclosing rectangle will be used.
GenParamName (input_control) attribute.name(-array) → (string)
Names of the generic parameters that can be adjusted for the sheet-of-light model.
Default: 'min_gray'
List of values: 'ambiguity_solving', 'calibration', 'method', 'min_gray', 'num_profiles', 'offset_x', 'offset_y', 'offset_z', 'scale', 'scale_x', 'scale_y', 'scale_z', 'score_type'
GenParamValue (input_control) attribute.value(-array) → (integer / real / string)
Values of the generic parameters that can be adjusted for the sheet-of-light model.
Default: 50
Suggested values: 'default', 'center_of_gravity', 'last', 'first', 'brightest', 'none', 'intensity', 'width', 'offset_scale', 50, 100, 150, 180
SheetOfLightModelID (output_control) sheet_of_light_model → (handle)
Handle for using and accessing the sheet-of-light model.
Example (HDevelop)
* Create the rectangular region in which the profiles are measured.
gen_rectangle1 (ProfileRegion, 120, 75, 195, 710)
*
* Create a model in order to measure profiles according to
* the sheet-of-light technique. Simultaneously set some
* parameters for the model.
create_sheet_of_light_model (ProfileRegion, ['min_gray','num_profiles', \
'ambiguity_solving','score_type'], \
[70,290,'first','width'], \
SheetOfLightModelID)
*
* Measure the profile from successive images
for Index := 1 to 290 by 1
read_image (ProfileImage, 'sheet_of_light/connection_rod_'+Index$'.3')
dev_display (ProfileImage)
dev_display (ProfileRegion)
measure_profile_sheet_of_light (ProfileImage, SheetOfLightModelID, [])
endfor
*
* Get the resulting disparity and score images
get_sheet_of_light_result (Disparity, SheetOfLightModelID, 'disparity')
get_sheet_of_light_result (Score, SheetOfLightModelID, 'score')
*
* Close the sheet-of-light handle once the measurement
* has been performed
Result
The operator create_sheet_of_light_model returns the value 2 (
H_MSG_TRUE)
if the given parameters are correct.
Otherwise, an exception will be raised.
Possible Predecessors
Possible Successors
set_sheet_of_light_param,
measure_profile_sheet_of_light
See also
clear_sheet_of_light_model,
calibrate_sheet_of_light
Module
3D Metrology