Web + VO + Database Technologies = HLA Footprints

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

JHU: Alex Szalay and Tamas BudavariNVO

Astronomical Application

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

Has HST 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 fieldI 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

HLA Footprints are spatially precise geometric descriptions of the HST observed areas in the skyCurrent holdings include reprocessed ACS fields (~20% of the completed observations), all sky WFPC2 and STIS

In transition are NICMOS, remaining ACS, FOS & GHRSCollaborations in process with NICMOS grism spectra, SPITZER….

Accessible via web client or programmatic interfaces

http://hla.stsci.edu/hlaview.html

Widespread Footprint Development

GALEX (STScI )NOAO VO PortalAladin (via APT)

IVOA (International Virtual Observatory) note for Footprint Overlay specification

VOServices (JHU)

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

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

Web components

Web portal built on a suite of web services (SOAP, http) using SOAReusable components mostly in form of XML

User requirements reduced significantlyNetwork access & a browser (FIREFOX)No installation required

Technologies are independent of platform and consistent with everyday lifestyle

XML, XSLT processors, Javascript, ASPX

Performance on the web client looks favorableaccept delay or switch to server side processing for large scale requestsJavascript security issues require proxy management

IFRAME

HLA Web Portal - Footprints

SQL ServerFootprint DB(with HTM)

IIS Web Server

Javascript UI manager (state and form control)

Object ParserXML Instance

ASPX + JS

VO Cone SearchVOTable

SOAP STCWeb Services

IFRAME

VOClients

GOOGLE

APT

SQL ServerDSS DB(with HTM)

RA,Dec,Radius

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 protocolsCone SearchSimple Image Access (SIA)

XML across the wire in VOTable or STC formatVO client applications can access HLA footprint programmatic services:

Datascope, Registry, Aladin, GOOGLE?

IVOA note on Footprint Overlay Specification

Database => Performance KeyMicrosoft SQL ServerClient development DOES NOT have to be on WINDOWS

Virtualization tools (Parallels, Remote Desk Top)FreeTDS

SQL scriptsmanage footprint computation of STC table objects/fieldsBuild and populate the different levels of representation

HTM (Hierarchical Triangulated Mesh) integrated for spatial search index

Coordinate based searchingAccessed via stored procedures and user defined functionsBounding circles for each region convex have htm ids

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 …)

JHU Spherical Library

Spherical geometry libraryExact equations for highly accurate region definitions, leverages HTMSTC elements are class types (region, convex, halfspace…)C# Assembly (SQL Server dll )

Operations for combining regionsUnions (outlines)Intersections (overlaps)

Mathematical Solutions AreaComplex regions can be made disjoint into convexes

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 overlapsHST unique distribution

sparse ALL-SKY

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 exposureDefine stacks using coarse-grained HTM matching for aperture vertices.

Visualization library

C# library with building canvas, frame, scaling and drawing methods using GDIDSS background image access using spherical projection and tiling algorithmsASPX is ~ html with C# class associated.

ASP controls for basic web gui featuresJavascript for interactive mouse and cursor stateEvent handling between the graphics and table paging control for selection

Challenges Ahead

Enhanced capabilities for visualizationCompletion of IVOA standard footprint servicesCommunity exchange of STScI Footprint schemaValidation of footprint representations between existing tools (Starview/APT, HLA, external…)Development of higher level product respresentations (MOSAICS, user-defined…)Storing Region binary blob representations