3 research outputs found
Dynamic simplification and visualization of large maps
In this paper, we present an algorithm that performs simplification of large geographical maps through a novel use of graphics hardware. Given a map as a collection of non-intersecting chains and a tolerance parameter for each chain, we produce a simplified map that resembles the original map, satisfying the condition that the distance between each point on the simplified chain and the original chain is within the given tolerance parameter, and that no two chains intersect. In conjunction with this, we also present an out-of-core system for interactive visualization of these maps. We represent the maps hierarchically and employ different pruning strategies to accelerate the rendering. Our algorithm uses a parallel approach to do rendering as well as fetching data from the disk in a synchronous manner. We have applied our algorithm to a gigabyte sized map dataset. The memory overhead of our algorithm (the amount of main memory it requires) is output sensitive and is typically tens of megabytes, much smaller than the actual data size
Management of spatial data for visualization on mobile devices
Vector-based mapping is emerging as a preferred format in Location-based
Services(LBS), because it can deliver an up-to-date and interactive map visualization.
The Progressive Transmission(PT) technique has been developed to
enable the ecient transmission of vector data over the internet by delivering
various incremental levels of detail(LoD). However, it is still challenging to apply
this technique in a mobile context due to many inherent limitations of mobile
devices, such as small screen size, slow processors and limited memory. Taking
account of these limitations, PT has been extended by developing a framework of
ecient data management for the visualization of spatial data on mobile devices.
A data generalization framework is proposed and implemented in a software
application. This application can signicantly reduce the volume of data for
transmission and enable quick access to a simplied version of data while preserving
appropriate visualization quality. Using volunteered geographic information
as a case-study, the framework shows
exibility in delivering up-to-date spatial
information from dynamic data sources.
Three models of PT are designed and implemented to transmit the additional
LoD renements: a full scale PT as an inverse of generalisation, a viewdependent
PT, and a heuristic optimised view-dependent PT. These models are
evaluated with user trials and application examples. The heuristic optimised
view-dependent PT has shown a signicant enhancement over the traditional PT
in terms of bandwidth-saving and smoothness of transitions.
A parallel data management strategy associated with three corresponding
algorithms has been developed to handle LoD spatial data on mobile clients.
This strategy enables the map rendering to be performed in parallel with a process
which retrieves the data for the next map location the user will require. A viewdependent
approach has been integrated to monitor the volume of each LoD for
visible area. The demonstration of a
exible rendering style shows its potential
use in visualizing dynamic geoprocessed data. Future work may extend this
to integrate topological constraints and semantic constraints for enhancing the
vector map visualization