3D Scanning

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3D Scanning
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How can we get the form?

• Projection

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Capturing design intents

• Generators
• Fillet radius change
• Knuckles

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Scanning

• 3D Scanning is the process of getting a set of
  surface points from a physical object
• Touch probe, optical, laser ranging, etc.
• Usually the points are structured

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3D Scanning equipment

• Contact type
• Touch probe scanner
• CMM
• Non-contact type
• Laser scanner
• Optical scanner

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Touch probe scanning
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Co-ordinate measurement
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Laser range scanning
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Optical scanning
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Application range

• From very small (tip of a drill bit) to very
  large (the Lee Ka Shing tower)
• Rigid or soft
• Coloured, glossy, transparent
• Restrictions Smoke, hair, cloud, very fast
  moving objects, etc.

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Data captured

• X Y Z location of points
• Freshly scanned data sets are usually structured,
  as a array in XY plane with different Z values
• May become un-structured, un-even spaced in all
  directions after re-sampling
• Usually stored as an ASCII text file

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Point cloud

• The collection of points is called point clouds
• A point cloud define the SURFACE of an object
• Some scanner (like CT and MRI) can measure
  physical properties of a objects entire solid
  mass, the collection of points is not point
  cloud, it is called VOXEL

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Level of details (LOD)

• LOD is determined by point density, which is
  determined during scanning
• LOD is proportional to file size
• Scanning itself is not selective, the result file
  size of a flat surface is the same as a carved
  board

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Shape consideration

• Optical scanner capture a 2D array of points each
  time
• Steep surface will have less points cast on it,
  thus fewer details

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3D Optical scanning

• Take pictures of the object
• Output a set of 3D points

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Shape VS position

• Point clouds gives only position information
• The shape of the object, if there is any, is not
  defined in the point cloud data
• Human can infer the shape from the clouds easily,
  but it is very difficult for machines

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Scan registration and merge
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Scanning and stitching

• Scan the object, coat the surface if necessary
• If the scan result cannot cover entire surface,
  scan from other angles
• Use point cloud manipulation software to align
  and merge scan results

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Re-sampling

• Re-sampling is the process to reduce the number
  of points or polygons so that the file size
  become manageable
• Adaptive re-sampling reduce more data points on
  smooth surface and keep more in regions that have
  abrupt changes

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Alignment

• Points are only x,y,z values

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Positioning and scaling

• Data from optical scanner is not necessary
  correct in size
• Positioning of point cloud is not necessary
  suitable for surface patching
• Alignment may need to be adjusted

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Tessellation of Point cloud
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Triangulation

• The process of converting point clouds to polygon
  models
• Triangulation is computation intensive
• If two points are close together, they are most
  probably on one surface
• If there are more that one possible shape, the
  shape that form a CONVEX HULL are more likely the
  correct choice

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Multiple solution
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Create curve network
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Feature curves

• Feature curves are curves that define distinctive
  visual features
• Sharp edges
• Fillets
• Holes
• 3D scanning cannot capture feature curves
  directly
• Irregularities may be corrected

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Repair model
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Surface modelling

• Generate surface patches using feature curves as
  guide lines
• Lofting is easier but may generate surfaces with
  unwanted undulation
• Sweeping and ruling generate fair surfaces but
  the feature curves are more difficult to draw
• Irregularities may be corrected

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NURBS surface creation
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Surface recreation

• Cut Sections by user defined plane, and then
  create surface according to these sections
• Draw 3D feature curves directly on the point
  cloud
• Full auto generation

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Steps to retrieve CAD from foam model

• Scanning and stitching
• Re-sampling
• Automatic surfacing or manual surfacing
• For manual surfacing
• Positioning and scaling
• Draw feature curves
• Draw Surface patches
• Check deviation

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Application
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Related applications

• Specialised applications
• Surfacer
• Rapid Form
• Raindrop Geomagic
• Scanning modules
• Pro/E, UG, CATIA, ALIAS