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This task shows you how to align a cloud of points with
surfaces. |
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Open the
Reposition2.CATPart model from the samples directory. |
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Click the Align with Surface
icon. A selection dialog box is displayed.
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Pick the cloud
to align, and the target surface(s). Push the Valid Surfaces
to end the selection of the surface(s).
Surfaces can be selected:
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by picking them in the geometry, |
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by picking them in the specification tree, |
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by using bounding outline or the standard selection
traps. |
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The target surface can be a join. |
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The target can also be a plane. |
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There is no limit to the number of target surfaces. |
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The Valid Surfaces button has turned to
Valid Trap.
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Define significant areas on the cloud to
align using the Alignment dialog box (its operating mode is
the same as
Activating a Portion of Cloud). Click Valid Trap between
each area definition.
These areas are the basis of the computation. They may have any shape, be
in any number. In this case, the significant area are the circular
tags.
| To activate an area by picking elements, select them and click
OK. |
| To create a single activation area by trap, draw the trap, modify
it when necessary and click Valid Trap, then OK. |
| To create several activation areas by traps, draw the first trap,
modify it when necessary, click Valid Trap to validate this
trap. Repeat these steps for each trap then click OK to
confirm the activation and close the dialog box. |
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Selective Display is not
available with this action. |
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Click OK when all areas have been defined.
Digitized Shape Editor proposes to compute the first move:
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Answer Yes: Digitized Shape Editor aligns the
center of gravity and the inertia axes of the parts, then the
position of each part. |
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Answer No: Digitized Shape Editor aligns only the
position of each part. This is recommended when the alignment of the
parts is already almost correct. |
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The cloud is repositioned on the surface(s): The output
cloud is a moved copy of the initial cloud, which can then be hidden if
necessary.
  
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The input cloud is duplicated and this copy is moved towards the target.
This new cloud appears in the specification tree. It has the name of the
input cloud, with its index increased by one. An element Axis_Systems is
also created in the specification tree, that contains the reference axis
system and the target axis system. These two axis systems can be used in an
Axis to Axis transformation with other geometrical elements (i.e.
replay the alignment). |
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Statistics
on the alignment operation are available.
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Push the More button.
The Statistics are displayed as soon as the computation
is started.
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This is the first section displayed. It indicates:
| the type of alignment performed (here it is a best fit
registration), |
| the number of points found in the mobile cloud, i.e. the cloud
to move, |
| the number of surfaces making the reference, i.e. the target. |
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This section is displayed when the computation is done. It
indicates:
| the number of iterations done, |
| the maximum deviation found between the points of the cloud
moved and the target surfaces, |
| the mean deviation found between the points of the cloud moved
and the target surface. This deviation should be as small as
possible. |
| the standard deviation, i.e. the dispersion of the points
around the mean deviation. A small standard deviation indicates
that most points are within the mean deviation, i.e. that there are
only few outliers. |
| the percentage of points of the cloud moved that are below the
mean deviation. |
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You can select the text and copy it to a word or data processing
software.
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| The Selective Display option is not available. |
| No need to define a computation area on the surface(s). |
| As long as you have not double-clicked to end the polygonal or spline
trap, you can undo/redo each pick of the polygonal trap. |
| You can use the function
Distance analysis to check the output accuracy. The target will be
the output cloud. Since a new output cloud is generated at each
alignment, you should repeat the distance analysis with each new output
cloud. |
| The result entity has the same structure as the input entity: scans,
grids or polygons. |
| You can repeat the process to improve the alignment, but this time,
do not accept the automatic first move. |
| The cloud to align should not contain a large amount of points. |
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