A 3D laser scanner is a high tech device that has the ability to accurately capture the surface of objects and provide real 3D data back to the user.
A 3D laser scanner works because of the principle of laser triangulation. By making a triangle between the scanner lens, laser, and object being scanned accurate 3D data can be obtained. The distance between the scanner lens and laser (parallax base) is known and with the angle of the laser given by the galvanometer, all information is provided to obtain x, y, z coordinates of the objects surface. The laser is swept across the object by the galvanometer, which rotates a small mirror that reflects the laser. The surface of the object is then focused through the lens and captured by the CCD inside the scanner. A dense point cloud is then produced through our software.
We Choose Specifics Based On Your Application
3D imagers are complicated imaging systems and their performance cannot be summed up with a single characteristic. 3D Digital Corp. is one of the few companies that provides a detailed description of the 3D scanner performance and thus allow a user to select a scanner that is ideally suited to their application and to know with high confidence that the scanner will be able to meet their requirements.
3D Laser Scanner Performance Factors
The performance of the 3d laser scanner is determined by a large number of factors. We describe the performance in terms of the following properties:
- Co-ordinate System
- Resolution: the smallest discernible feature on the target. Alternatively, an equivalent definition is the minimum separation between two target features where the two features are distinguishable in the image.
- Accuracy: the standard deviation of the range measurement. This is often referred to as the ‘error’ in the range measurement.
- Point density: The distance between neighboring range measurement points.
- Depth of field: This describes the range over which the 3d laser scanner can obtain an accurate image.
- Field of view: This determines how large a target can be imaged in a single scan.
3D Laser Scanner Co-ordinate System
We define a right handed co-ordinate system with an origin at the center of the 3d laser scanner imaging lens. The x-axis is parallel to the long axis of the scanner front plate (this is horizontal in the usual scanning geometry). The y-axis is parallel to the short axis of the 3d laser scanner front plate (vertical in the usual scanning geometry), and the z-axis is the range, or the distance perpendicular to the scanner front plate. The co-ordinate system is illustrated in the following figure.
3D Laser Scanner Resolution
The resolution of the 3d laser scanner refers to the ability of an imaging system to measure the angular separation between two objects (or object features) that are close together. The resolution is a limitation of the scanner in the x-y dimensions. For example if a target has embossed lettering, and the font size is smaller than the resolution of the scanner then the text will not be legible in the scanned image, regardless of the height (z-depth) of the lettering.
The resolution is determined by three major factors: the laser stripe width, the lens focal length, and the CCD resolution. The resolution is dependent on the target distance and generally gets worse with increasing range.
Accuracy of 3D laser scanners
While the resolution affects the image quality in the x and y dimensions, the accuracy refers to the image quality in the z (or depth, or range) dimension. 3DD scanners calculate the range of each point on the target object. CCD noise, imperfect optics, and fundamental laws of physics all result in some error in the calculated range. It is not possible to design a 3d laser scanner that does not have some error. The accuracy is a measure of this error. It is defined as the standard deviation of the difference between the measured range and the actual range to a target. The range error is approximately Gaussian in nature. This implies that if we scan a perfectly flat plane, at a fixed range of 245mm (10″), and if the accuracy of the scanner is 250microns (0.01″), and we build a histogram of the ranges of each of the points it would look like the one shown in the following figure. 65% of the range points will lie within +/- 1 standard deviation from the mean, i.e.: +/-250microns (+/- 0.01″). 95% of the range points will lie within +/- 2 standard deviations from the mean, i.e.: +/-250microns (+/- 0.02″).
Point Density of 3D laser scanners
Point density refers to the distance between neighboring range measurement points. This will be different in the x and y dimensions. The x density is determined by the number of scan lines, while the y density is determined by the CCD resolution. For example if the user selects to scan with 500 lines and the CCD has 480 vertical pixels the point density is 500 x 480. At a range of 300mm (12″), this corresponds to a point spacing of 0.61mm x 0.64mm (0.024″ x 0.025″).
3D laser scanner Depth of Field
The depth of field or ‘depth of focus’ refers to the range of distances over which a focused image is obtained. As with a normal camera our products are focused for a particular range. Objects outside this range will result in blurred images and inaccurate range data. Therefore the 3D Digital software automatically discards range data for objects outside the design range. This ensures that the output data is all within our specified accuracy. The following figure illustrates the concept of depth of field.
Field of View on 3D laser scanners
The field of view of the scanner determines the largest object that can be imaged using a single scan. The field of view is normally expressed as an angle and it describes the angle of a cone within which an object must be placed for the 3d laser scanner to be able to image it. The field of view cone is illustrated in the following figure. The tip of the cone is at the center of the imaging lens. Obviously the larger the target to be imaged the further away from the scanner it must be placed. A disadvantage of this is that the accuracy of the scanner generally decreases at longer ranges, so a large field of view is generally very attractive as it allows large targets to be imaged with high accuracy.
Learn More about 3D Laser Scanners
Learn more about how the software and 3d laser scanner hardware work together and what it can be used for: