NC-measuring machines, video technology and different laser technologies enable the 3d digitizing. For the moment one looks for possibilities of generating from a cloud of points developing thereby as high-quality a geometry as possible (e.g. CATIA-Solid-E with CSG(Construktive Solid Geometry) - tree, STEP advanced boundary representation).

From the experiences, which the author made in the context of a CAD project with the so called "intelligent digitization" in the 2d area, a suggestion will be made, as by interactive connecting of 3d digitizing, simple surface recognition
and a construction system an optimal working process for the geometry reconstruction ("reverse engineering") can be arranged. 

2. Intelligent 2d digitizing

The pending function consisted of the fact that some thousand "2d copying templates", which were used to cut the raw material for the production of airplane sheet metal bending parts,had to be transformed into analytic geometry, which were necessary for programming a numerical controled machine tool.

With the "intelligent 2d digitizing" consciously the automatic producing of a cloud of points by automatic tracing the contour was eliminated.

Rather became a graphically interactive 2d NC programming system, which was operated by means of a ADAGE 4250 scope attached to  a IBM MVS computer, interconnected with a Nestler digitizing table as follows:

• At the Nestler digitizing table the digitization magnifying glass was replaced by a swivelling measuring cut, with which the outer contour the "2d copying template" could be touched.
• The loadable Microcode of the Nestler digitizing table was programmed in such a way, that a 6 byte long information could be transferred  to a serial interface, if one of the control keys were pressed.
• The 6 byte long information contained beside the 2 byte X- and Y-coordinates also of specifications concerning the pressed key, with which additionally to the built-in function keys the program flow of the 2d NC programming system could be influenced.
• Over a interface devices operating into the internal data bus of the ADAGE 4250 and a changed Microcode of the ADAGE 4250 the 6 byte could be put into the 2d NC programming system. (at the transition to IBM 5086 scope the same was managed by means of a serial port, which was operated as a additional graphic address).

• The template to be digitized was fixed on the Nestler digitizing table.
• The position of the x axis and the coordinate system origin was determined by measurement of 3 points.
• For the geometry definition in the 2d NC programming system required point data were consulted by the Nestler digitizing table, whereby the most important function keys (POINT, LINE, ARC, CIRCLE) could be pressed from Nestler digitizing table.
• For check additional points could be measured, read into which 2d NC programming system and compared with beforehand produced geometry.

• a genuine reconstruction of geometry could be executed,
• comparatively few expenditure had to be operated and
• violations apparently happend when using the templates did not appear in the reconstruction result.

3. Interactive 3d digitizing

Similarly to the "intelligent 2d digitizing" the "interactive 3d digitizing" should be a type of "reverse engineering" -- i.e. determining high-quality a geometry (CSG - Constructed Solid Geometry, volume, surface, curve, point) from 3d measuring points -- , which combines on a workstation the following components :

• 3d design system (e.g.  CATIA)
• 3d digitizer (e.g. coordinate measuring machine, 3d laser scanner, 3d picture investigater, ...)
• Control window for the 3d digitizer
• Video picture of the object, which is be digitized

The arrangement shown should enable the digitization and transformation of measured geometry (points, polygone, point samples) into geometry with higher order (curves, surfaces, limited surfaces) and the following assembly to structured volumes in one processing step.

Advantages:

• The point quantity which can be measured can be drastically reduced.
• The surface allocation of measuring points is problem-free, since the measuring points are processed immediately in each case.
• In the 3d digitizer higher functionality (e.g. rule geometry recognition) can be carried out.
• Manufacturing or use-conditioned irregularities of the digitization object can be eliminated.
• Rational combination of digitization and reconstruction of component geometry.