3D Scanning

How can we get the form? Projection

Capturing design intents Generators Fillet radius change Knuckles

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

3D Scanning equipment Contact type  Touch probe scanner Touch probe scanner  CMM CMM Non-contact type  Laser scanner Laser scanner  Optical scanner Optical scanner

Touch probe scanning

Co-ordinate measurement

Laser range scanning

Optical scanning

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.

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

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 object’s entire solid mass, the collection of points is not point cloud, it is called VOXEL

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

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

3D Optical scanning Take ‘pictures’ of the object Output a set of 3D points

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

Scan registration and merge

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

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

Alignment Points are only x,y,z values

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

Tessellation of Point cloud

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

Multiple solution

Create curve network

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

Repair model

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

NURBS surface creation

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

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

Application

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