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

Background - 1 IVOA Trieste meeting presented the concepts for a new footprint service specification DAL working group STANDARD Ongoing development of Use Cases with specific development on the Observation Data Model 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 - 2 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) HST APT (will be demo’d in Apps session) Continued to have working group IVOA telecons conducted to discuss the different approaches and definitions of ‘footprints’ convergence *appears* to be on the horizons

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 VODataService schema to include

Observations With Regions Observation and Characterization Data models allow provide a mechanism for including STC Regions with Science Data Footprint service methods provide capabilities of intersecting Regions, operations STC Region Intersection (odm1, odm2)

Examples of Footprint hierarchy HST WFPC2 ACS Mosaic Mosaic Association Combined (Filter, channel) Exposure Visit 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 Registry schema component VODataService.xsd Coverage/footprint/serviceReference => IVO-ID Identifier URI

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 Move forward to construct the IVOA footprint standard Working Draft Accommodate all levels of complexity Develop Use Cases with Observation Data Model/Characterization/Provenance Footprints mean different things Layers of geometric descriptions Build on IVOA standard STCRegion

Footprint Service Related Links NVO Trac Page http://trac.us-vo.org/nvo/wiki/Footprints JHU VO Services http://voservices.org/ IVOA Tech Note http://www.ivoa.net/Documents/latest/Footprint.html HLA Portal http://hla.stsci.edu