Temporal and Multidimensional Support in a GIS

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Temporal and Multidimensional Support in a GIS

• Steve KoppESRI

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The Requirements

• Support temporal and multidimensional data
  structures and file formats.
• Provide visualization and data exploration tools
  specific to multidimensional data.
• Perform traditional GIS operations and analysis
  on multidimensional data.
• Build new analysis tools to take advantage of
  higher dimensionality.

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The First Step

• Extend existing functionality to support time and
  multidimensional data
• Add support for the netCDF data format
• Dynamic Temporal Graphing
• Mapping change through time
• Support temporal animation
• Initial focus
• Data access and visualization
• Earth science modeling

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Temporal Data Structures for GIS

• Vector Data Structures
• Points, Lines, Polygons
• Add attributes, fields and relationships to
  storage and query of time.
• Raster Data Structures
• A table pointing to a collection of raster
  datasets with a time attribute.
• Multidimensional Arrays
• Already support time as a dimension
• e.g. netCDF, HDF, GRIB, etc.
• New to most GIS users, common to Earth science
  modeling community.

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What is netCDF?

• An array based data structure for storing
  multidimensional data.
• N-dimensional coordinates systems
• X coordinate (e.g. longitude)
• Y coordinate (e.g. latitude)
• Z coordinate (e.g. altitude)
• Time dimension
• other dimensions
• Variables support for multiple variables
• Temperature, humidity, pressure, salinity, etc
• Geometry implicit or explicit
• Regular grid (implicit)
• Irregular grid
• Points

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NetCDF in ArcGIS

• NetCDF data is accessed as
• Raster
• Feature
• Table
• Direct read,no scratch file
• Also write GIS data to netCDF

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NetCDF Tools

• Make NetCDF Raster Layer
• Make NetCDF Feature Layer
• Make NetCDF Table View
• Raster to NetCDF
• Feature to NetCDF
• Table to NetCDF
• Select by Dimension

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Using NetCDF Data

• Behaves the same as any layer or table in
• Display
• Same display tools for raster and feature layers
  will work on netCDF raster and netCDF feature
  layers.
• Graphing
• Driven by the table just like any other chart.
• Animation
• Multidimensional data can be animated through a
  dimension (e.g. time, pressure, elevation)
• Analysis Tools
• A netCDF raster layer will work just like any
  other raster layer, feature layer, or table.
  (e.g. create buffers around netCDF points,
  reproject rasters, query tables, etc.)

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Maps and Graphs from netCDF
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Emphasis on Data Exploration

• Support animation of graphs temporally
  synchronized with maps
• Support Linking and Brushing
• Mechanisms used to visually explore the
  connections between information in maps, graphs
  and tables.
• Connecting multiple visualizations provides more
  information than considering the component
  visualizations independently.

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Dynamic Linking between Maps, Graphs, and Tables
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Intelligent Temporal Axes
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Animation
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Provide Appropriate Cartography for Earth Science
Modelers
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National Weather Service forecast for July 18th
from NDFD netCDF
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Some obstacles

• Date standards not widely honored
• Too many flavors of n-dim formats
• Loose standardization
• No best practices guidelines
• Weak coordinate system handling in n-dim formats
• Horizontal mostly lat/long WGS84
• Other dimensions such as vertical and time often
  not specified.