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

2. 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 *

3. 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

4. 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

5. 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)

7. 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

8. 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)

9. 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

10. 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

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