HLA Footprints for Multipurpose Science
Gretchen Greene, Stephen Lubow, Tom Donaldson, and Kim Gillies (Space Telescope Science Institute)Tamas Budavari and Alex Szalay (Johns Hopkins University [JHU])
ABSTRACT

Footprints from the science observations of the Hubble Space Telescope are defined by a set ofhierarchical geometric regions of instrument coverage; exposures, combined observations, highlevel science products, and mosaics. In the growing global community of networked applications,the science end-user has several use cases for visualizing and accessing footprint data including
scientific proposal preparation, research and analysis of generated science products, andinteroperability between archives for correlation of coverage. The Hubble Legacy Archive (HLA)at Space Telescope Science Institute, in coordination with ESO-ECF and CADC, has developed aweb based science user interface built on a VO service oriented architecture system to enable
varying levels of astronomical community access to science products derived from the HST archive.
In this ADASS poster paper we describe new features and technologies for the HLA footprintcomponent web browser visualization tool and the underlying footprint services utilized by the HST
Astronomers Proposal Tool (APT) in compliance with an IVOA standard data access protocol. The
service infrastructure is based on a high performance spherical geometric model developed byJohns Hopkins University (JHU) and database search algorithms co-developed by STScI and JHU.

Proposal Planning Observation Footprints

Uses JHU Spherical Geometricand HTM Library
A mathematically accurate library for performing
geometric operations on defined region celestial
areas
Compute Region Bounding Circles and Region
convexes for instrument apertures with HTM index
Region operations with C# assembly
SQL Server Database + .NET
Query Optimizer Index built on HTMIDHTM Search Functions
Nearest neighbor
BBoundingdiCiCircles
lRange Query

Each triangle is subdivided
into 4 triangles by connecting
the side-midpoints ofneighboring sides

Such subdivisions may continue to any desired depth(within the limits of computation)

Displays HIERARCHY of scienceobservation products:
Exposures

High Level Science Products
Table of exposure/product science
properties (a.k.a. metadata)
IVOA standard DAL service with SpaceTime Coordinate footprints

Tessellation of the sphere in triangles allowing
spatial indexing by location on the sphere.
The Sphere istreatedinitially as anoctahedronArchive Footprints
Sky Region Outlines of observation
apertures or combined coverageImage background with multi-color
Digitized Sky Survey (DSS 2)

Combined Sequential ExposuresMosaics *NEW for ACS*

Hierarchical
Triangular Mesh(HTM)

APT interfaces to VO Standard
SIA services Accessed throughAladin contain HLA Footprint
STC descriptions

ys

HLA Observed Footprints
Help Astronomers Plan
where to place New
Observation apertures

Advanced Concepts
Usingi archivehi footprints,ficompute theh groupsof intersecting exposures for mosaics
Algorithm: friends-of-friends
Area computations

World Wide Telescope with HLA Footprints

Region intersections between archives:Search for centers within polygon region
Unions, Intersections and Areas combinedwith standardVO STC RegionTypes

References
fAladin Search Results provide
Graphical Visualization of HLA
Observed Footprints overlay withPlanned Observation Footprints•Gray, J., Szalay, A.S., Thakar, A.R., Fekete, G., O'Mullane, W.,
Nieto-Santisteban, M.A., Heber, G., & Rots, A.~H. 2004, ThereGoes the Neighborhood: Relational Algebra for Spatial DataSearch, ArXiv Computer Science e-prints, arXiv:cs/0408031• Szalay, A.S., Gray, J., Fekete, G., Kunszt, P.~Z., Kukol, P., &Thakar, A. 2007, Indexing the Sphere with the Hierarchical
Triangular Mesh, ArXiv Computer Science e-prints,arXiv:cs/0701164