The basics of Scanning
Step 1: Determination of Intent
- How will this image be used?
- What are your tolerance requirements?
- How will it be used?
- What is the actual value of Tolerance to be met.
All these questions help to determine the required type of data output and Scanning Technique which achieves the desired result quickly and efficiently and above all if the scanning process is feasible compared to developing a design through a traditional CAD workflow.
Step 2: Selection of Appropriate Acquisition Technology
The advancements in technology over the last 20 years have brought several Scanning technologies. Below is a list of Scanning Technologies along with their strengths.
- Structured Light – Is typically a two-camera, stereo system. It yields clean data. Its limitations are translucency/transparency, deep colors opposing the light spectrum of the projected light and the need for both cameras to see the geometry being captured.
- Portable Scanning Arms – These make use of Lasers. They are fast, flexible and adaptable for various mounting conditions and scanning different surface colors. Their limitation is the length of the arm which may require multiple setups for part sizes beyond the arm’s reach.
- Long Range Laser Scanners – Are preferred in situations where large objects such as Air Craft need to be scanned with reasonable tolerance.
- CT (X-ray) – These Scanners come in play when the need obtain internal data arises.
Step 3: Data Processing
Once 3D geometric data (Point Cloud) has been captured, the common next step is converting the XYZ 3D data points into a polygon model. For this purpose a Software is utilized. The software connects the dots with a series of triangles to create a representative skin. There are various tools that can accomplish this goal. Most hardware suppliers provide this direct output from their scanners, others rely on third party software to run the calculations.
There are many software packages that allow you to manipulate the data, including smoothing out imperfections, closing small or even absurdly large holes within a reasonable assumed precision.
Finally, validation has to be conducted to show deviation of the scanned object back to the CAD model being developed. This deviation is represented typically by a color map, with each color representing the 3D distance each point varies from its CAD model counterpart. Once this evaluation is complete and meets the expectations determined, the CAD model is ready to be delivered.