A Hierarchical Vector Data Model for Distributed Geospatial

Processing

Eric B. WolfBarbara P. ButtenfieldUniversity of Colorado

at BoulderNSF BCS 0451509

Presentation for the AAG National Conference 2007

The Problem

Spatial data is compiled by NMAs at fixed scales:

• E.g., 1:24,000, 1:100,000, 1:1,000,000 Mixing fixed-scale data corrupts topology. Incorrect generalization -> incorrect modeling

output. Lack of persistent storage for generalized

representations.

Presentation for the AAG National Conference 2007

Our Project: MRVIN

MRVIN: Multiple Representations for Vector INformation. A hierarchical architecture for vector geospatial data. Provides multiple representations across a range of

resolutions. Preserves topology within each data theme and between

data themes. Sustains distributed data retrieval through standard

interfaces.

Presentation for the AAG National Conference 2007

Previous Work

Ramer 1972, Douglas-Peucker 1973 Ballard 1981 Herschberger and Snoeyink 1992 Saalfeld 1999 Bertolotto and Egenhofer 1999 Buttenfield 2002

Presentation for the AAG National Conference 2007

Ballard Strip Tree (1981)

• HierarchicalMBR

• Efficient storage search

• Complete RDP order

Creation of Strip-Trees

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MRVIN Data Structure

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Mathematical Topology

A topology on a set X is a collection T of subsets of X having the following properties:

1. Ø and X are in T

2. The union of elements of any

subcollection of T is in T

3. The intersection of the elements of any finite subcollection of T is in T

Munkres, J. R. 2000. Topology. Second ed. Upper Saddle River, NJ: Prentice Hall. P. 76.

Presentation for the AAG National Conference 2007

Examples of Topologies

Equivalent Topologies Comparable Topologies

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Internal & Relative Topology

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Self-Crossing Feature

Preserving Topology

“If two convex hulls do not overlap, the contents of those hulls will not overlap.” (Saalfeld 1999)

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Preserving Topology in Multi-Part Features

Compound Vectors are stored as “groves” of “trees”

The convex hull for each tree is calculated and stored.

A convex hull for the grove is calculated and stored.

Saalfeld’s test is applied among all trees in each grove and among groves.

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Preserving Relative Topology

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MRVIN Architecture

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Extending MRVIN to points and polygons. Managing dimensional collapse (when a

polygon becomes a line or a point) ArcGIS script like “TerraServer Download”. Merge MRVIN into PostGIS and extend

Minnesota Map Server to create tiles from MRVIN for WMS access.

Keyhole Markup Language output for Google Earth.

Future Research

Presentation for the AAG National Conference 2007