Increasing population density and rapid urbanization lead to a burst of multifunctional, complicated and comprehensive buildings. Within these buildings, people often have difficulty to locate themselves or get to their destinations. Although real-time outdoor navigation has been widely applied, it is not the case in indoor space due to the lack of feasible or affordable indoor positioning technologies. Instead of a thorough solution, an alternative approach is proposed to indoor positioning and navigation in this paper. This approach is physically based on a mobile device, such as a smart phone, equipped with acceleration sensors. Accessible space of a building is represented with a 3D geographic information system network model, based on which, all points of interests are located spatially. Initial input from a user is used to figure out its current location, as the origin of navigation, and then the approach can generate an optimal path to the destination. While the user moves along this path, its linear displacement can be calculated with acceleration sensors in real time and further matched onto this path as user's real-time location. Accordingly, real-time guiding information can be delivered to users like outdoor navigation. This approach has been implemented in Android-based devices, and a series of experiments are conducted to demonstrate and validate the proposed approach.

Background: Liposarcoma is common in adults. However, its occurrence in the retropharyngeal space is extremely rare, and no cases of liposarcoma in the prevertebral space have been reported before.Case presentation: A 78-year-old man presented to the Otolaryngology Department with a 1-year history of progressive dysphagia and a 1-month history of dyspnea and dysphonia. A computed tomography scan of his neck demonstrated a large retropharyngeal mass. Magnetic resonance imaging was performed to further characterize this mass. Based on the above examinations, retropharyngeal liposarcoma was first made. The patient underwent transoral surgical excision with the help of nasal endoscope. During surgery, the tumor was found to lie in the prevertebral space. Combine with histological examination, the diagnosis was modified to liposarcoma of the prevertebral space. Conclusions: It’s difficult to distinguish the enormous retropharyngeal tumors and prevertebral tumors using imaging. Complete excision via transoral approach maybe enough for these tumors.