The data management layer accesses the 3D models and ground-texture images persistent on the flash disk of the mobile phone through an independent thread. To reduce the data size of the 3D models, the original .3ds file created from 3D Max Studio software is compressed.
The locator component aggregates the positioning information either from the built-in positioning sensors in the smartphone, a GPS receiver, and a Wi-Fi or Bluetooth chip, or any external positioning device, such as also the multi-sensor positioning (MSP) device developed in this project. It forwards the positioning information including the location and heading information to the route plan component and the 3D visualization engine to accomplish the navigation functions.
Figure 2 shows the overview of the mechanism for delivering the location-based services. The services are classified into two categories: the static services and the dynamic services. The static services include those services that are not changing in time. For example, POIs (points of interest) belong to this category of service. The static services are stored in a database that can be downloaded from the Internet by the users in advance. The users can store the database in the memory card of the phone before running the 3D personal navigation and LBS software. With this approach, it saves the data transmission fee for the end-users when accessing the LBS. The dynamic services cover those services that change in time. For example, a piece of real-time news is one of the typical dynamic LBS. For accessing the dynamic LBS, Really Simple Syndication (RSS) technology is adapted in our implementation.
The LBS client component is implemented so that the handset will pull automatically the news in the background in real time via a widget reader embedded in the LBS client component. Whenever new information is uploaded to the LBS server or to the registered web pages, mobile users will be notified.
In addition to RSS technology, another approach to broadcast LBS information is considered in the system: to disseminate the LBS information via an SBAS (satellite-based augmentation system) pseudolite. The dynamic LBS information (e.g., a short message) can be first encoded into a user-defined SBAS message. The message encoded is then sent to a pseudolite from which the message is broadcast. The corresponding SBAS message can, in fact, be received by any SBAS-enabled receiver located within radio coverage area of the pseudolite.
However, the encoded LBS message can be decoded only with the receiver that has a special firmware, developed in this case by the Finnish Geodetic Institute (FGI). Having received and decoded the LBS messages transmitted from the pseudolite with a dedicated receiver, for example the MSP device part of the more advanced demonstration scenario of the project, the content of the message is then encoded to a user-defined NMEA (National Marine Electronics Association) message and transmitted to a mobile phone in the vicinity via a Bluetooth connection as shown in Figure 2. This solution of LBS data distribution is available only to a very limited number of users with receivers carting a special firmware developed by FGI.
3D city modeling
Due to the memory limitations of a mobile phone, there are certain requirements for the 3D models applied. In our study, a test scene for model reconstruction is focused on a street in Espoo, Finland, in an ordinary residential area. A vehicle-borne mobile mapping system called ROAMER, developed by FGI, performed the data acquisition. It consists of a carrying platform, a positioning and navigation system, and a 3D laser scanner system. With the ROAMER system, visible objects can be measured with an accuracy of a few decimeters with a maximum vehicle speed of 50-60 km/hour, and the data for the desired objects can be collected within the range of several tens of meters.
A large amount of data is produced from the system, and noise and outlier points are needed to be removed. Valid data is classified into different point groups using an automatic algorithm developed by FGI. These point groups include buildings, trees, roads, and poles. Models are then reconstructed based on these classified point groups.