Mobile mapping is now firmly established as the preferred method for quickly, efficiently and accurately mapping outdoor areas of all sizes and types. It can be done efficiently from air, land and sea. Applanix POS products pioneered and developed the technology, but can the tremendous benefits of mobile mapping be realized indoors, where there is no access to GPS satellites for accurate location determination?
Accurately modeling indoor spaces has many important uses including:
After nearly half a century of developments in satellite navigation, GNSS-aided inertial solutions can achieve centimeter accuracies where we have a clear view of the sky. That’s no help indoors, however, where GNSS signals cannot be received. Many different indoor mapping methods have been proposed and tested, including emitted RF ranging (using WiFi, RFID, pseudolites, Bluetooth beacons, or other beacons of opportunity), SLAM (simultaneous localization and mapping), lidar, close-range photogrammetry, pulsed signals from lights, magnetic distortions, and sonic imaging. They require some form of infrastructure (such as WiFi hotspots) often not available in buildings under construction or dilapidated, or installing and revisiting targets, which is one of the pain points of static surveying.
Applanix chose to tackle this challenge by building on its decades-long expertise in inertial navigation. However, an inertial system inherently suffers from drift. How can you constrain it without pairing it with a GNSS receiver or first surveying an indoor space by traditional methods? Applanix’s answer, the Trimble Indoor Mobile Mapping Solution (TIMMS), combines a mechanical approach with a software one. Its rigid wheels prevent it from moving sideways and are instrumented to provide a very precise measurement of its forward motion. It then uses a point-cloud data adjustment (PCDA) software — a SLAM-type algorithm — to analyze the point cloud and find commonalities in different passes. As a result, the inertial system only requires a single precise survey control point, which can be obtained by conducting a very quick traverse. (The best absolute accuracy requires multiple control points, however, which are recommended for very large facilities.)
An Applanix team captured comprehensive 3D scans and spherical imagery of 1.75 million sq. ft. of floor space in two terminals at Los Angeles International Airport in just 32 hours — compared to up to six weeks of field work and about as long for processing and modeling that it would have taken for a conventional static scanning survey. Read the full LAX Case Study.