Transportation networks, such as streets, railroads or metro systems, constitute primary elements in cartography for reckoning and navigation. In recent years, they have become an increasingly important part of 3D virtual environments for the interactive analysis and communication of complex hierarchical information, for example in routing, logistics optimization, and disaster management. A variety of rendering techniques have been proposed that deal with integrating transportation networks within these environments, but have so far neglected the many challenges of an interactive design process to adapt their spatial and thematic granularity (i.e., level-of-detail and level-of-abstraction) according to a user's context. This paper presents an efficient real-time rendering technique for the view-dependent rendering of geometrically complex transportation networks within 3D virtual environments. Our technique is based on distance fields using deferred texturing that shifts the design process to the shading stage for real-time stylization. We demonstrate and discuss our approach by means of street networks using cartographic design principles for context-aware stylization, including view-dependent scaling for clutter reduction, contour-lining to provide figure-ground, handling of street crossings via shading-based blending, and task-dependent colorization. Finally, we present potential usage scenarios and applications together with a performance evaluation of our implementation.

1. Interactive Rendering and Stylization of Transportation
Networks using Distance Fields
Matthias Trapp, Amir Semmo, Jürgen Döllner
Hasso Plattner Institute, University of Potsdam, Germany

2. INTRODUCTION

3. Towards Cartography-oriented Stylization

4. Paris Street Map – 1780
P1: contour lines surround fine-textured fills or solid colors
to add visual contrast and improve figure-ground perception
P2: primary streets overlap secondary or tertiary streets in
hierarchical representations of street networks; wavy or fuzzy
to express uncertainty
P3: names follow principal line directions and are placed within
streets or outside line segments

5. London Street Map – 1913

6. London Underground Map – 1933

7. Modern Tourist Map of Paris
P7: yellow established as a conventional color tone for main
streets, with a discrete gradation towards grey and white
shading for tertiary roads
P6: streets are tinted using qualitative color schemes to represent
street classes and distinguish them from the underlying terrain
P5: a hierarchy of emphasis is drawn among reference elements,
such as different line weights and colors to portray different
grades of roads
P4: dynamic filtering and scaling of geometric features improves
perception of roads at high view distances and avoids
cluttering.

8. Conceptual and Technical Requirements
 Pre-processing of discrete level-of-details consume additional memory and yield
incoherent rendering when switching between these levels during zooming or within
perspective projection.
 Levels-of-Detail should be computed during rendering based on viewing settings
 Increasingly detailed networks require high amounts of main/video memory.
 Network representation should exhibit a small memory footprint and fast updates
 View-dependent cartographic stylization of transportation networks are key features for a
number of applications.
 Rendering technique should provide a sufficient parameterization, i.e., covering level-of-detail
rendering, interactive filtering, and highlighting

9. RELATED WORK

10. Related Work :: Overview
Street Rendering Approaches
Object-space Approaches
Geometry-based Approach
Texture-based Approach
Screen-Space Approaches
Stencil-based Approach
Discard-based Approach

11. Geometry-based Approach
Basic Principle:
 Pre-compute geometry at different LoD
 Forward rendering geometry
 Most flexible approach w.r.t. stylization
Limitations:
 High memory consumptions for complex networks
 No transitions between static LoD
 High rendering costs

12. Texture-based Approach
„Interactive 3D Visualization of Vector Data in GIS”
O. Kersting, J. Döllner, ACM GIS 2002
Basic Principle:
 Generate texture trees from geometry
 Off-screen rendering at different resolutions
 Use for texturing during scene rendering
Limitations:
 Relies on data pre-processing
 Requires intermediate representation
 Suffers from texturing artifacts

13. Stencil-based Approach
„High-Quality Cartographic Roads on High-Resolution DEMs”
M. Vaaraniemi, M. Treib, R. Westermann, WSCG Journal 2011
Basic Principle:
 Generate shadow volume per street segment
 Avoid cracks between segments using cap cones
 Enables distance-based scaling of street segments
 Rendering using shadow volume approach
Limitations:
 Requires additional data structure (volumes)
 Limited styling capabilities (color + outline)

14. Discard-based Approach
„A screen-space approach to rendering polylines on terrain”
D. Ohlarik, P. Cozzi; SIGGRAPH Poster 2011
Basic Principle:
 Extrude polylines to walls
 Compute intersection with terrain
 Discard fragments accordingly
 Avoid dashing and smearing
Limitations:
 Stylization with single color only
 No distance-dependent segment width

15. Distance-fields for Stylization Parametrization
„ Real-Time Rendering of Water Surfaces with Cartography-Oriented Design”
A. Semmo, J. E. Kyprianidis, M. Trapp, J. Döllner; CAe 2014

16. APPROACH

17. Overview of Approach
Forward Rendering Pass Deferred Rendering Pass

18. Open Street Map (OSM) Data Representation

19. Overview of Distance-Field Generation

20. Geometry Generation
Attributed Vertex Cloud
+
Geometry Shader
+
Vertex Pulling

21. Encoding of Distance using Texturing

22. dresult = min(dsource , ddestination)
Blending Modes
No Blending Min-Blending
Distance Field Colored Distance Field Colored

23. Result: 2D Texture-Array
Memory consumptions: #layer  width  height  precision (3 * 32 Bit = 12 Byte)

24. Evaluation of Distance Fields :: Procedural Textures
Procedural textures evaluated on a per-fragment basis:
 Deferred texturing based on distance fields
 Application of procedural and image textures possible
 Bottom-up compositing based on street rank
“Improved Alpha-Tested Magnification
for Vector Textures and Special Effects”
Chris Green; SIGGRAPH 2007

25. Final Compositing Step
Bottom-up evaluation of each layer (street category) and blending

26. RESULTS & DISCUSSION

27. Application Examples :: Distance-based Evaluation

28. Application Examples :: Stylization Variants

29. Application Examples :: Regions-of-Interest

30. Application Examples :: Regions-of-Interest

31. Performance Evaluation
 Test data sets of different complexity
from Open Street Map (OSM) data base
 Approach is fill-limited w.r.t. number of
street categories to render
ID Data Set # Nodes #Ways
A Berlin 1 5571 1028
B Istanbul 2004 263
C Berlin 2 9502 1766
A B C A B C A B C
390 x 260 670 x 450 1280 x 800
1 Category 3 2.9 3 3 2.9 3 25.5 25.4 25.3
2 Categories 3.2 3.3 3.4 3.2 3.3 3.4 29 29 29.2
4 Categories 4.1 4.1 4.2 4.1 4.2 4.2 36.1 26.2 36.2
8 Categories 5.5 5.4 5.5 5.7 5.6 5.8 50.1 50.1 50.2
0
10
20
30
40
50
60
Milliseconds

32. Limitations
Distance-field generation:
 Intrusion
 Protrusion
Memory consumptions for large numbers of categories
Intrusion
Protrusion

33. Future Work :: Geometry Draping
Draping
Digital Elevation Model Result
Planar Network Geometry

34. Future Work :: Geometries
 Generate alternative geometric representations
 View-dependent adaptation of geometric representations

35. Conclusions
 A concept for high-quality cartographic rendering exemplified
for complex street networks.
 Interactive hardware-accelerated rendering technique having
minimal memory footprint for network representation.
 Interactive stylization and colorization using deferred texturing
based on distance fields generated on per-frame basis
 Potentials for future research

36. Questions & Comments ?
Contact:
 Matthias Trapp / matthias.trapp@hpi.de
 Amir Semmo / amir.semmo@hpi.de
 Jürgen Döllner / juergen.doellner@hpi.de
Publications: www.4dndvis.de/publikationen.html
This work was funded by the Federal Ministry of Education and Research (BMBF),
Germany within the InnoProfile Transfer research group "4DnD-Vis".

37. Interactive Rendering and Stylization of Transportation
Networks using Distance Fields
Matthias Trapp, Amir Semmo, Jürgen Döllner
Hasso-Plattner-Institut, University of Potsdam, Germany