Issues in terrain visualization for environmental monitoring applications
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Issues in Terrain Visualization for Environmental Monitoring Applications. Ricardo Veguilla [email protected] Nayda G. Santiago [email protected] Domingo A. Rodriguez [email protected] Electrical and Computer Engineering Department

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Issues in Terrain Visualization for Environmental Monitoring Applications

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Issues in Terrain Visualization for Environmental Monitoring Applications

Ricardo Veguilla [email protected]

Nayda G. Santiago [email protected]

Domingo A. Rodriguez [email protected]

Electrical and Computer Engineering Department

University of Puerto Rico, Mayagüez Campus

June 23, 2006

Raw Data


Computed Data



WALSAIP: Wide Area Large Scale Automated Information Processing


Data Representation


Computational Signal

Processing Systems

Signal Data


Information Rendering


Signal Conditioning


Sensor Array


Pre-processing Stage

Processing Stage

Post-processing Stage

WALSAIP-VTE (Visual Terrain Explorer)



Information Rendering System


Automated Data


Data Acquisition

Data size, complexity, and performance

  • 3D visualization is computationally expensive

  • We want to visualize large, complex geometrical models

  • Critical for interactive terrain visualization due to the sheer size of the data sets

Level of Detail

Level of Detail (LOD)

  • Premise: It is inefficient to use many polygons to render object that will only contribute to a few pixels of the rendered scene.

  • Conclusion: Use less detail for small, distant portions of the scene.

  • Approach: Use geometric simplification operations to eliminate redundant information while satisfying both performance and visual accuracy constrains.

Our Goal

Review available terrain rendering LOD techniques, with interested in:

  • How to exploit video card (GPU) processing capabilities

  • Handling data larger than available memory (out of core, distributed computing)

  • Identify best approach for a future implementation of the VTE

Basic Components

  • The initial mesh: A polygonal representation of the terrain at either the minimum resolution level (base mesh) or the maximum resolution level (full mesh)

  • Updates operations: Operation which simplify or refine a mesh.

Characteristics of LOD Algorithms

  • LOD Granularity

  • LOD Distribution

  • Processing direction

  • Terrain Data Structure

  • LOD Data Structure

76 polys

2,502 polys

69,451 polys

251 polys

LOD granularity

  • Discrete LOD: finite set of pre-computed LODs

  • Continuous LOD: further simplifies discrete LODs to produce a continuous spectrum of detail

251 polys

69,451 polys

N polys

LOD distribution

  • Uniform

  • View-dependent

Processing direction

Top-down (refinement or subdivision algorithm)

Bottom-up (simplification or decimation algorithm)

Terrain data structure

Height fields


Triangulated Irregular Networks


LOD data structure

Quadtree: a rectangular region recursively subdivided into four uniform quadrants.

Bintree (Binary triangle tree) : a rectangular region is recursively subdivided into two triangles.

Survey of Algorithms


  • Traditional Approach

    • 80’s

    • The basic unit is the triangle

    • Traditional LOD techniques generally aimed to produce the ideal level of detail

  • Modern Approach

    • 2000’s

    • Basic unit is the triangle cluster or patch

    • Concerned with maximizing GPU usage and minimizing CPU usage

Traditional Approach

Real-time, continuous LOD rendering of height fields

  • Using a quadtree with discrete LODS generated off-line

top-down refinement

bottom-up simplification


  • Uses two ordered priority queues: one for split operations and the other for merge operations.

View-dependent Progressive Meshes

  • a TIN-based, view dependent terrain LOD algorithm

  • Continuous LOD is produce by recursively removing triangles from off-line generated blocks of terrain.

Modern Approach

Geometrical MipMapping

Quadtree technique that work on blocks of uniform detail

Simplification based on vertex removal

Selection based on worst-case view parameters

Eliminates cracks by changing vertex connectivity at the block boundary

Triangle cluster Techniques

  • Cluster: small triangle meshes optimized for GPU processing

  • Cluster are cached on the video card memory.

  • Hierarchy is used for view culling


Frustrum Occluded Cluster

Inactive Cluster

Visible Cluster

Occluded Cluster

ACL = Active Cluster List

Geometry Clipmap

A multi-resolution mesh formed by combining nested concentric grids center about the view position

Resulting view

View culling


  • In Use of triangle cluster patches as basic rendering unit allow:

    • maximizing GPU usage*

    • better coupling of the geometry and the texture

    • out-of-core operation*

    • The ideal level of detail (an irregular mesh) is in compatible with GPU maximization (which require regular meshes)

*points of interest for the WALSAIP-VTE project




Automated Terrain

LOD Generation

Terrain Visualization

Terrain Data



  • Java and OpenGL implementation with LOD based on GeoMipMaps.

  • Future research on out-of-core data management for remote data acquisition


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  • Ricardo Veguilla

    [email protected]

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