This may be more of what they want or need to know about the complexity of a mobile mapping system (MMS), but for those interested, here is an explanation of the average Joe can understand. When you have a mobile mapping system to reach their place of work for a laser scanner, the system seems little more than an elegant piece of PVC attached to the top of a 4WD SUV. Do not be fooled by its simple appearance. Inside is a modern miracle … a set of systems for setting up independent and incredibly complex, when assembled, produce what would have seemed impossible not so long ago. This little white box of wonder, when you turn, begins to communicate with many satellites in space, and you can find. The positions were established. Movement and the games are monitored at breakneck speed with each reading time stamped so that every few seconds, when the team catches its breath, the independent pieces of data are united together again, along with corrections complex to reveal an elegant reproduction of the surface is only driven past. It’s really a thing of beauty.
MMS providers use this technology experts amalgam of technologies to offer its customers mobile laser scanning services that produce a cloud of X, Y, Z point in the state plane coordinate systems or similar. Here is an overview of the different technologies used and how they unite to produce an accurate description in 3-D of the areas surveyed:
Determining the location – GPS
Mobile Mapping Systems (MMS) using the Global Positioning System (GPS) to determine where we are at any given time. The accuracy of raw GPS data is not suitable for our purposes so we use one of the three technologies to correct the raw position information. If we have a checkpoint near known work, which can set up a GPS base station on the item and use measurements of the position of the GPS satellites to determine the difference between the actual measured position and then every second . This error or “differential” is transmitted by radio to the mobile scanner and GPS data collected by the scanner to correct every second. This method is called real time kinematic, or RTK. If no checkpoint is available, we can establish one and, using industry standard tools to determine your exact location at a later time. Using RTK, we can establish our position within ± 1 inch of East and Northing and ± 2 inches tall.
The second method we use to determine our position is similar to the RTK, it is called Virtual Reference Station or VRS. In this method, we subscribe to a service that has a number of base stations (VRS Network), created in a given area. We use the wireless data link for GPS corrections of this network and GPS data in the mobile scanner is fixed as the RTK method. The accuracy of this system is comparable to that of RTK.
The third method we use to determine the position of the uses OmniStar ®, a private satellite-based correction. It provides corrections similar to that of VRS, except it uses a satellite receiver to receive data instead of a wireless link. OmniStar ® accuracy is slightly lower than RTK or VRS ± 4 inches. We can mix and match these technologies when needed – for example, we use RTK to exploration, but to define the control point using the Omnistar ® system to eliminate the need to determine the position of the control point later.
How to measure the changes of direction – Inertial Measurement Unit
Using our GPS technology is measured accurately our position about once per second. However, we are constantly changing direction. At 5 miles per hour, traveled about 7 meters per second. During that second, we can change our direction of travel (departure) of many degrees. Inertial measurement unit (IMU) measures changes in the scanner of the game 100 times per second. The IMU accuracy is ± 0.1 degrees (~ 0.17 feet to 100 feet away). The position of the mobile scanner automatically restarts when receiving a new GPS position “fix” every second so any small error in the IMU, it is allowed to accumulate.
How to collect the data of Surveying – The laser module
Thanks to the GPS and IMU technology, we can track the exact position of the mobile scanner at each point in time. The GPS and IMU are mounted within the scanner cover. Outside of housing, we have a rotating laser module. This scanner has a laser distance measuring mounted at right angles to the direction of the vehicle or vessel. The laser measures 36,000 points per second, turning at 10 rpm and has a range of up to 450 feet. The accuracy of the measurement of distance is ~ ± 2 inches. The distance between points is controlled by laser RPM and vehicle speed. Usually generate a cloud of points with the points of ~ 0.5 to 2 feet away. Data can be diluted to reduce the size of data sets if desired. If better data coverage is necessary, adjustments to the control software can be changed. The mobile scanner can explore all that is passed in front of top, bottom or sides of the scanner.
How to correct an irregular terrain – Pitch and Roll sensors
The mobile scanner is mounted on a vehicle or vessel. In a perfect world, soil or water body would be perfectly horizontal. Since this is obviously not the case, correct the data by measuring the pitch (angle up or down) and roll (left or right angle) to the browser using pitch and roll sensors. These instruments measured the field and shooting 100 times per second with an accuracy of ± 0.01 degrees (~ 0.02 feet to a distance of 100 feet) Because these instruments measure the attitude of the mobile scanner so often, that can travel on rough terrain or rough sea at a reasonable speed, without seriously affecting the accuracy of the data.
Summary
Scanning LiDAR or mobile phone, because sometimes called can provide unprecedented efficiency and accuracy in many studio applications. Whether you need to measure the value of stocks, make a detailed planning of the mines, as beach erosion, encroachment of vegetation to determine the utility right of ways or to solve a number of problems or engineering study, Mobile Lidar can provide the solution to their problems.
