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Web + VO + Database Technologies = HLA Footprints. STScI : Gretchen Greene, Steve Lubow, Brian McLean, Rick White and the HLA Team JHU : Alex Szalay and Tamas Budavari NVO. Astronomical Application.

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Web vo database technologies hla footprints l.jpg

Web + VO + Database Technologies = HLA Footprints

STScI: Gretchen Greene, Steve Lubow, Brian McLean, Rick White and the HLA Team

JHU: Alex Szalay and Tamas Budavari


Astronomical application l.jpg
Astronomical Application

Archival Research is a value added product to observation planning as well as data mining

  • HasHST observed in this location of the sky?

    • Which wavelength?, how long?, what instrument?, what was the exact coverage with respect to object XYZ?

  • Show the coverage for a high level product, e.g. Hubble Deep Field, GOODS mosaics, ALL overlapping ACS exposures of a specific field

  • I have a transient even (e.g. VOEvent notification), what is the coverage in HST?

  • How does HST coverage compare to another observatory coverage?

  • Large scale distributed spatial queries

    • NVO search portal

Hst footprints in the hla l.jpg
HST Footprints in the HLA

  • HLA Footprints are spatially precise geometric descriptions of the HST observed areas in the sky

  • Current holdings include reprocessed ACS fields (~20% of the completed observations), all sky WFPC2 and STIS

    • In transition are NICMOS, remaining ACS, FOS & GHRS

    • Collaborations in process with NICMOS grism spectra, SPITZER….

  • Accessible via web client or programmatic interfaces

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Widespread Footprint Development

The (GALEX) MAP - (adaptable to other missions)

  • GALEX (STScI )

  • NOAO VO Portal

  • Aladin(via APT)

    • IVOA (International Virtual Observatory) note for Footprint Overlay specification

  • VOServices (JHU)

Sky section or image plane: pans, zooms, downloads data.

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Web components

  • Web portal built on a suite of web services (SOAP, http) using SOA

    • Reusable components mostly in form of XML

  • User requirements reduced significantly

    • Network access & a browser (FIREFOX)

    • No installation required

  • Technologies are independent of platformand consistent with everyday lifestyle

    • XML, XSLT processors, Javascript, ASPX

  • Performance on the web client looks favorable

    • accept delay or switch to server side processing for large scale requests

    • Javascript security issues require proxy management

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HLA Web Portal - Footprints

Javascript UI manager

(state and form control)


VO Cone Search



Object Parser

XML Instance


IIS Web Server






Web Services

SQL Server

Footprint DB

(with HTM)

SQL Server


(with HTM)

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Virtual Observatory

  • Footprints are built on IVOA standard STC XML data model (Space Time Coordinate)

    • Regions, Convexes, Reference Frames + much much more

  • Data Access Layer services are built on standard VO protocols

    • Cone Search

    • Simple Image Access (SIA)

  • XML across the wire in VOTable or STC format

  • VO client applications can access HLA footprint programmatic services:

    • Datascope, Registry, Aladin, GOOGLE?

  • IVOA note on Footprint Overlay Specification

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Database => Performance Key

  • Microsoft SQL Server

  • Client development DOES NOT have to be on WINDOWS

    • Virtualization tools (Parallels, Remote Desk Top)

    • FreeTDS

  • SQL scripts

    • manage footprint computation of STC table objects/fields

    • Build and populate the different levels of representation

  • HTM (Hierarchical Triangulated Mesh) integrated for spatial search index

    • Coordinate based searching

    • Accessed via stored procedures and user defined functions

    • Bounding circles for each region convex have htmids

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DB Schema STC

  • DB Tables map to XML elements in the schema

  • HLA Science table associates regions to science metadata tags (target, exposure, dataset, filter, PI …)

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JHU Spherical Library

  • Spherical geometry library

    • Exact equations for highly accurate region definitions, leverages HTM

    • STC elements are class types (region, convex, halfspace…)

    • C# Assembly (SQL Server dll )

  • Operations for combining regions

    • Unions (outlines)

    • Intersections (overlaps)

  • Mathematical Solutions

    • Area

    • Complex regions can be made disjoint into convexes

Hierarchical representations l.jpg
Hierarchical Representations

  • Exposures (Level 1)

  • Stacks(Level 1 – visualization optimization)

  • Combined sequential exposures (Level 2)

  • Groups (Level 3 & 4)

    • Mosaics, weight maps, use-defined, custom constrained

      • Fractals

  • Performance Issues for crowded overlaps

  • HST unique distribution

    • sparse ALL-SKY

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Exposure Stacks

  • Many cases where exposures lie on top of each other (form a stack)

  • Can reduce overhead by graphically representing exposures in a stack by a single member exposure

  • Define stacks using coarse-grained HTM matching for aperture vertices.

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Visualization library

  • C# library with building canvas, frame, scaling and drawing methods using GDI

  • DSS background image access using spherical projection and tiling algorithms

  • ASPX is ~ html with C# class associated.

    • ASP controls for basic web gui features

    • Javascript for interactive mouse and cursor state

    • Event handling between the graphics and table paging control for selection

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Challenges Ahead

  • Enhanced capabilities for visualization

  • Completion of IVOA standard footprint services

  • Community exchange of STScI Footprint schema

  • Validation of footprint representations between existing tools (Starview/APT, HLA, external…)

  • Development of higher level product respresentations (MOSAICS, user-defined…)

  • Storing Region binary blob representations