View - and Scale-Based Progressive Transmission of Vector Data Padraig Corcoran, Adam Winstanley, Peter Mooney - National University of Ireland Maynooth Michela Bertolotto - University College Dublin

1. View- and Scale-Based Progressive
Transmission of Vector Data
Padraig Corcoran, Peter Mooney, Adam Winstanley and
Michela Bertolotto.
Department of Computer Science,
National University of Ireland Maynooth.
School of Computer Science and Informatics,
University College Dublin
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2. Introduction
● Web application development is in the middle of
a paradigm shift.
● Web-GIS applications still linger behind
desktop-GIS in terms of:
● Functionality.
● Interface.
● User Interaction.
● This can be attributed to the manner in which
spatial data is transmitted.
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3. Tile-based Transmission
● Predominant transmission methodology
● Vector data converted to raster maps tiles on the
server.
● Map tiles transmitted to client.
● Used by Google Maps and OpenStreetMap.
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4. ● Advantages:
● HTML has native support for images.
● Image compression is an advanced science.
● All data requests are pre-computed.
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5. ● Disadvantage:
● Vector data is not transmitted therefore the client
cannot perform spatial queries or adapt the
visualization.
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6. Vector-Based Transmission
● Can we transmit vector data and maintain the
advantages of tile-based transmission?
● Development of such technology is a main goal
in the field of Progressive Transmission.
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7. Progressive Transmission
● For large data sets a trade off exists between:
● Transmission of high levels of detail.
● Transmission in reasonable time.
● Progressive transmission attempts to optimize
this trade-off for vector data.
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8. ● Progressive transmission is characterized by
two properties:
● Data is transmitted in the form of increments or
refinements.
● To reduce redundancy data is not re-transmitted.
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9. View- and Scale Based
Transmission
● In order to structure existing research in this
field we propose a classification.
● All methods for progressive transmission may
be classified as view- or scale-based.
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10. View-Based Transmission
● Data is transmitted progressively as a function
of changing viewing window.
Time (Progressively Changing View) 10

11. Scale-Based Transmission
● Data is transmitted progressively as a function
of changing scale.
Time (Progressively Changing Scale) 11

12. Scale-Based Implementation
● Refinement is the inverse of generalization.
● All refinements are actually generalizations and
therefore satisfy the same objectives. 12

13. Fusion View- and Scale-Based
● Both approaches reduce the volume of data
transmitted in different ways.
● To maximise efficiency concepts from both
must be fused.
● Currently the most advanced fusion method is
that of Li et al. 2009
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14. Li et al. Methodology
● The vector data is divided into tiles.
● The subset of tiles a user views is determined.
● Each of these tiles is then transmitted using a
scale based transmission strategy.
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15. ● Disadvantages:
● Features which span multiple tiles must be
segmented and rejoined.
● Such features cannot be generalized.
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16. Proposed Fusion Methodology
● A transmission method which removes the
requirement for tiles is proposed.
● Firstly all features are generalized in a manner
which maintains topology (Corcoran et. al, IJGIS
2011).
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17. ● Features are then inserted into an R-tree
(spatial indexing method).
● Given a viewing window the features contained
within this window are progressively transmitted
while maintaining topology (Corcoran. et al,
Agile 2011).
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18. Implementation
● Implemented using client server model.
● Server client communication uses HTML 5
WebSocket API.
● Client rendering uses HTML 5 Canvas API.
Sequence Diagram 18

19. Transmission Example
Large Scale Map 19

20. 20

21. Quantitative Results
Comparison of data volume transmitted.
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22. Conclusions
● We provide an analysis and propose a
framework to classify existing progressive
transmission methods.
● Subsequently, a new fusion method is
proposed.
● Request are computed on the fly; future work
will aim to reduce computational complexity.
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