Footprint Service Specification IVOA Interop Meeting Trieste 2008 Gretchen Greene and Tamas Budavari

Objectives and Definition Request IVOA consensus that we need a new service specification for footprints –Begin draft of DAL standard footprint service –Continue ongoing development of Use Cases Footprints are spatial geometric descriptions otherwise known as “regions” Footprint services will transfer regions –Ideally no/minimal transformation required –compliant with VO query language (e.g. ADQL ‘Region’) * Conceptually REGION is a well defined entity based on an IVOA standard data model *

Background IVOA standard spatial data model, Space Time Coordinate (STC) v 1.3 approved and endorsed by TCG STC Reference implementations created for managing spatial geometric descriptions of multiple survey archives footprints JHU VO Footprint Services STScI HLA (Hubble Legacy Archive) footprints S*AP abstraction of STC in the form of Utypes for association with observation data references IVOA Technical Note for Footprint Overlay Specification Visualization Tools (Aladin, VIRGO) 4/08 IVOA telecon conducted to discuss the different approaches and definitions of ‘footprints’ convergence *appears* to be on the horizon

Service Definition - key concepts Geometric descriptions will use STC –STC/X XML region descriptions –STC/S string region description ( ADQL ‘Region’) Footprints are hierarchical, examples next slide… –Archive aggregate descriptions (full survey) –Mosaics –Exposures, Spectra, Observation Service handles represented by IVO-ID URI Registry footprint metadata may require extension schema to handle full capability Near term goal VODataService propose to include ‘types’

Examples of Footprint hierarchy Registry schema component VODataService.xsd –Coverage/footprint/serviceReference => IVO-ID Identifier URI HST ACS Mosaic Combined ( Filter, channel) Visit Exposure WFPC2 Mosaic Association Exposure HLA Footprint Service IVOIDs map into the Product Levels. Two examples of footprint service handles: Ivo://hla.stsci.edu/hst/acs/mosaic Ivo://hla.stsci.edu/hst/wfpc2/association SDSS Footprint Service IVOIDs map similarly. Examples Ivo://jhu.edu/sdss/stripe/stave/primary/footprint Ivo://jhu.edu/sdss/tile/plate/wedge/sectorlet/sector/specfootprint

Footprint Service Methods BASIC Footprint Service: Contains(Point [,tol,types,survey]) FindByPoint(Point [,types,survey]) FindByKey(keyword [,types,survey]) GetRegion(region,format) GetTypes() GetEnvelope() **** NON EXACT GetCover(survey, lod, format) GetFootprint() *** EXACT GetMasks() GetArea() ADVANCED Footprint Service: Intersect () – boolean Overlaps((Region|Mask) [,types,survey]) Intersection(region, region, format) Union(region,region,format) DistinctUnion(region,region,format) Difference(region,region,format) Dilate(region,buffer,format) Erode(region,buffer,format)

Reasons to support New Service Scalability of distributed spatial correlations –Complexity of unions and joins not primitive type handling Spherical geometry requires advanced capability –Spatial partitioning and indexing –Highly complex regions - fractals Data model accurately describes the information –Curation and preservation of regions should be considered Expertise in this area has proven solutions that have been seriously studied and evaluated over many years –GIS community interest –commercial database incorporated spatial indexing

Summary Need IVOA footprint standard –Accommodate all levels of complexity –Work with observation data models Footprints mean different things –Layers of geometric descriptions Build on IVOA standard STCRegion

Footprint Service Related Links NVO Trac Page JHU VO Services IVOA Tech Note HLA Portal