How to align a scanned source mesh (from
some area of an object) to a destination mesh (or surface) by specifying
regions where the data matches on both.
This is useful for updating
a digital model based on scan data, after the physical objects have
been modified in some areas, and re-scanned.
The input to this tool
consists of a source mesh, (also referred to as the scan - for example,
a re-scanned area of an object), and destination meshes or NURBS
surfaces to which the source mesh must be aligned.
The source mesh is transformed
so as to minimize the average deviation between the source mesh
position and the destination meshes/surfaces.
During the iterative
alignment of the scan data, you can restrict the rotation and translation
along world space axes, as well as specify a rotation pivot or an
axis of rotation.
To ensure fast and accurate
results, an area of the source mesh should not have changed, and
should match an area on the target object(s). However, the tool
will still operate even if these areas are not exactly identical.
To align a mesh to other
meshes or surfaces
- Choose Mesh > Mesh Positioning
❒.
- Select the mesh (scan) you want to position.
The mesh is highlighted in white.
- Select one or more destination meshes
or NURBS surfaces to align to.
The targets are highlighted in purple.
NoteIf you need to de-select
or select another source mesh or destination geometry at this point,
press the Pick Mesh or Pick
Destination button, and click the geometry to select
or de-select.
- Press the Go button
at the bottom of the window.
A new series of buttons appears at the bottom
of the window.
NoteIf Show
Deviation Map was turned on in the control window, the
source mesh is shaded with a deviation color map.
Method 1: Using regions
for positioning
- Press the Match Region button.
- Select the region(s) of the mesh that
are matching the targets, by clicking down points to form polygonal
selection area(s). Press the Select Region button
before selecting each additional region.
All selected regions are highlighted in blue.
If you do not select any regions, the whole
mesh is used.
NoteTo de-select all regions, press the Clear
Input button.
- To specify a rotation pivot or rotation
axis, press the Add Pivot Constraints button,
then click on the mesh in one or two locations respectively.
The points you clicked
appear as locators lying on the source mesh. You can reposition
them with the mouse.
NoteWhen specifying a rotation pivot or axis,
the Transform Mode option is automatically
set to Rotate Only to make the results
of the re-positioning more predictable.
- Press the Go button
at the bottom of the window.
- The source mesh (scan) is translated
and rotated (according to the options specified in the control window)
so that the selected regions achieve the best possible match with
the targets.
- A deviation color map is displayed on
the source mesh (if Show Deviation Map is turned
on.)
- The Deviation Average, Standard
Deviation and Deviation Maximum values
are displayed in the control window.
- Press the Go button
repeatedly to iteratively converge on the best placement.
The alignment should
improve and the deviation between source and target decrease with
each iteration. Note that convergence of the iterations is only
guaranteed when Transform Mode is set to Translate
and Rotate.
NoteUse Edit > Undo to
undo the last iteration.
- You can also change some of the options
in the control window, then press the Go button
to recalculate.
- If you want to undo all the iterations
and return the source mesh to its original position, press Undo
All in the control window.
Method 2: Using Feature
Points for positioning
Instead of selecting
matching regions on both the source and destination geometry, you
can also specify matching points.
This method is most useful
when the source or destination has features (for example grooves
or bumps) not present on the other, or when the source is not already positioned
in the vicinity of the destination.
NoteWhen
using this method, Acceptable Distance, Sample
density, Percentage of vertices, Increase
overlap by sliding mesh, Consider local features and Transform
Mode are all ignored. Both translation and rotation are
always applied during the positioning.
- Follow steps 1 to 4 from the previous
workflow.
- Press the Feature Points button
at the bottom of the window.
New buttons appear.
- Click down on the source mesh to position
the first set of points.
The
points appear as numbered bullets: 1,2,...N
- Press the Points On Destination button.
- Click on the destination meshes or surfaces
to position the points that should match the ones on the source
mesh.
The
points appear as numbered bullets: 1,2,...N
NoteAt any time, you
can add additional points to the source mesh or destination geometry
by first pressing either the Points On Mesh or Points
On Destination button.
- Once all points are selected, press Go.
The source mesh is positioned
so that the two sets of points achieve the best fit: point N on the source attempting to match
point N on the destination.
