Laser Scanning is present in many aspects of life and ranges from the stella to the microscopic. The most commonly found are Lidar - which is an aircraft based scanning, Terrestrial - which is a ground based scanning activity and Metrological which is a precision component based process. The the different types of scanning relate to three different levels of perception and vary greatly in the way they are employed the accuracy and range of the data and they produce. They share a common process that includes the recording of points on the surfaces of realworld objects. The points are usually described by their position (usually X,Y,Z) the strength of the returned signal and or the colour. the colour is usually mapped to the points by a separate photographic process. We can look at the three types more closely...
It is important to understand the "Accuracy" of Laser scanned data. Laser scanned data is composed of many variable on top of the direct laser measurement and as each type attempts to be more accurate then the variables are removed. the varaible present in airbornse scanning are much higher than in scanning used for metrology where the position of the scanner is measured and controled with great accuracy. There are some problems with speciffying the accuracy of laser data. These relate to knowing where the scanner is and its orientation during the scanning process the more we can control this the more accurate we can make our data.
Lidar is an Acronym that is derived from "Light Detection and Ranging" and has similarities to its radio cuisin Radar. Lidar is an airborne technology that is used mainly for large scale geographic surveys. Its role is to gather Information over large areas. It is the least accurate of the three types listed here. Typical accuracies of Lidar Scanning are in the Order of tens of centimeters and have probably has most variables of all the scanning methods listed. A lidar survey has to account for the motion of the aircraft that carries the equipment, in pitch, yaw, roll, drift and forward speed. after it has caluclated these it can then work out the x and y elements of the measured point (northings and easting) It then has the task of calculating the elevation or z element of the point.
Terrestrial scanning as its name suggests has the scanning equipment fixed for each scan. This differs from Lidar where the scanner is contiually in motion. This allows terrestrial scanning to eliminate a lot of the variables associated with the position of the scanner. So for each scan the variables are much more controlled and the accuracy of the data is significantly better (it is usually to within a few millimeters. Unfortnatly a terrestrial survey rarely consists of one scan, it may consist of many hundreds of scans. The majority of errors in a terrestrial survey will come from the registration of one scan to another. Bad registration can reduce scan data accuracy significantly.
Metrology is the science of mesurement and it is the focus of this group of scanners to get the maximum accuracy possible. These scanners are usually used for reverse engineering off components and the position of the scanner is stricly contriolled. The scanner is restrianed with an arm so the problem of registration is removed as the position can be accuratly measured. This type of scanning is generally done in controlled environments typically in ispection rooms or in production environments. this removes variable s associated with the weather and temperatures.