How can I reverse engineer an organic shape or surface? This is a question that we are being asked increasingly often. We have found the best way is to work from a 3D laser scan.
How do laser scanners work?
The term laser scanning very often refers to laser triangulation; it is based on the principle of emitting many thousands of laser points in the form of a line on to a surface of the object to be scanned then recording the refection via a receiver (usually high power optics). Surface shape and texture can then be determined by the deformation in this laser line, as the distance and angle from laser source to receiver is known the system can then establish the depth of each point on the surface via Pythagoras theorem. As this process happens with many thousands of points per second the system is able to determine the shape of the object being scanned.
The result of this scan data is widely known as a point cloud, this provides a wealth of information but can be tricky to handle. The real problem lies with the amount of data. To export the point cloud data into a modelling software would put a real strain on the processing power and graphics of even the very top spec work stations. So the first step in any post processing is to scale down the information, very often this is in the form of a STL Polygon mesh.
What is a polygon model?
The software will look at a set of points and attempt to connect them with a polygon. The software then looks to connect these polygons together and display a surface. The size and number of polygons will vary with scan resolution and surface topography. This mesh surface often represented as an STL format is perfect for metrology, as the surfaces represent the point cloud data and can be compared directly to the CAD model. Modern scanning software also often allow for feature recognition or identification allowing more traditional geometric tolerances to checked.
Can I produce a CAD model from an STL file?
The short answer is yes, however the polygon mesh is not quite as useful for 3D modelling as it is for metrology. As it is very often an STL format the surfaces carry no thickness or density and depending on the resolution level are not able to form constant curvatures (effectively they are a 3D dot-to-dot with straight lines). Meaning that parametric modelling software’s cannot determine inner and outer surfaces or solids. This is where companies such as Qualis Engineering excel, whilst there are many forms of software that claim to be able to directly convert STL files to parametric CAD entities such as STP files these options really produce the required result from scan data, at best they will convert the individual facets (the polygons) that make up an STL model directly into CAD surfaces resulting in a model made up of thousands of very small surfaces giving rise to large problems in later workflow processes.
Qualis Engineering has over ten years experience working with 3D scan data and STL polygon mesh models and using this experience alongside the latest reverse engineering software we are able to deliver high quality CAD design models that are ideal for reproduction, simulation or modification of any physical object.
For more information on STL model to CAD conversions drop us an email info@qualisengineering.co.uk or take a look at our website: https://www.qualisengineering.co.uk/
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