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 CMM

Non-contact type Laser 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 softColoured, glossy, transparentRestrictions: Smoke, hair, cloud, very fast

moving objects, etc.

Data captured

X Y Z location of pointsFreshly 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 sizeScanning 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 objectOutput 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 intensiveIf two points are close together, they are

most probably on one surfaceIf 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 modelScanning and stitchingRe-samplingAutomatic surfacing or manual surfacingFor 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