How to carry out three-dimensional reverse scanning on large objects

In the practice of three-dimensional scanning, it often happens that the object that customers need to scan is beyond the normal scanning range, which is much larger than our normal scanning object size.

For this kind of objects, if we use the conventional scanning method to find and splice them automatically, we will face two problems.

First, too many stitching times lead to an increase in accumulated errors. Whether it is a 3d scanner based on natural light or laser principle, stitching is to stitch the generated point clouds, and the stitching is concentrated on the adjacent images. If there is no obvious feature in the overlapping area of adjacent images, or there is a mismatch in several parts with similar features, the registration error will continue to expand in the process of continuous stitching, leading to error accumulation and unsatisfactory stitching effect.

Second, stitching errors are prone to occur, which affects scanning efficiency. In the process of stitching, if stitching is carried out continuously, once the features of adjacent images are not enough, stitching failure and error will easily occur, which will affect the scanning speed.

So, how to scan such an object?

At present, the common practice in the industry is to use special photogrammetry equipment for auxiliary measurement. Auxiliary equipment has many names, such as three-dimensional optical industrial close-range photogrammetry system, photographic three-dimensional photogrammetry system, three-coordinate digital close-range photogrammetry system, global photogrammetry system, all-digital photogrammetry system, optical three-coordinate and so on.

With the help of photogrammetry equipment, the conventional three-dimensional scanning process of large objects is as follows:

1. Place the coded reference point, non-coded reference point and calibration scale on the measured object.

2. Measure the surface of the measured object from different angles with a camera, and extract all reference points and scales.

3. Input the data into the software, get all the reference points and unify them in the same coordinate system.

4. The 3d scanner is used for multi-angle measurement, so that the reference points of scanned data can be automatically spliced in the obtained coordinate system, and the splicing error of repeated overlapping measurement can be reduced.

General photogrammetry equipment can measure objects ranging from several millimeters to tens of meters, which is very suitable for 3d scanning of super-large objects such as ships, vehicles and airplanes with 3D scanners. After obtaining the three-dimensional scanning results, the comparison can be reversed, which is of great significance to the production inspection department.

At present, there are mainly American GSI and German AICON abroad, and there are Xibo 3XDTP and Vision Wei MPS in China. However, when it is applied to the reverse scanning of large objects, a 3d scanner is needed, and both AICON and Xibo 3d have matching 3D scanners, which are more prominent in the reverse scanning of large objects.