Practical Footprints bin/twiki/bin/view/IVOA/DALBasicFootprintHere Gretchen Greene, Jonathan Fay, Thomas Boch, Francois Ochsenbein, Doug Tody

Driving Factors for Footprints for Simple DAL Spatial Region descriptions are fundamental, i.e. FOOTPRINTS First order question – What is the COVERAGE? which leads to identification of datasets of interest Key data provider services implementing Footprints with slightly variant representations Clients REQUIRE near term stable and CONSISTENT representation (e.g. WWT, HLA, TAP clients in Dev, Aladin, VAO DDT, and on…) Existing Astronomical client tools are required to custom parse services – maintenance and performance impacts I VOA Interoperability – RWG Session 1

Whats Doable - Near Term! January AAS Meeting – Austin Texas Tagup meeting to discuss having agreed upon use of footprints for Simple DAL services OUTLINES of spatial regions – straightforward LETS not WAIT for standards process to complete to move forward with common implementations Consensus in approach, shared in IVOA DAL working group for wider review Draft IVOA Technical Note replaced action with DALI spec (DAL wg will complete this) I VOA Interoperability – RWG Session 1

DAL Regions Existing simple DAL services now using make- shift regions (SIA v1, Cone, etc.) STC –s placeholders utype confusion predates this discussion OBSCore Standard Region serves BASIS Column Name s_region unitless AstroCoordArea semantic type Region covered as specified in STC or ADQL Utype derived from Characterization Model Char.SpatialAxis.Coverage.Support.Area I VOA Interoperability – RWG Session 1

SIA v2 REGION Optional REGION parameter In the case of services which return archival images (whole images) the REGION parameter may be used to specify the spatial region to be searched more precisely than can be done with POS,SIZE. The region is specified as a STC-S formatted string. When REGION is used the search region is no longer limited to nonrotated rectangles, e.g., circles, ellipses, rotated regions, and arbitrary polygons may be specified as well. Example: Circle ICRS A service may implement the REGION parameter. A service which implements REGION should support at least the ICRS and GALACTIC coordinate frames, if appropriate for the data being accessed. It is an error if the REGION parameter is I VOA Interoperability – RWG Session 1

Compound Regions Often case where there are more complex descriptions required E.g. multiple spatial areas with lots of space between, combine exposures with holes, mosaics, Allow s_region to support these with STC-s semantics for Union, Intersection, negation, Difference UNION (Polygon ra1 dec1 ra2 dec2 ra3 dec3 ra4 dec4 Polygon ra1 dec1 ra2 dec2 ra3 dec3 ra4 dec4) I VOA Interoperability – RWG Session 1