1. Sep 8, 20082008 NVO Summer School1 WCSFixer A Web-Enabled IRAF Plate Solver Mike Fitzpatrick, NOAO T HE US N ATIONAL V IRTUAL O BSERVATORY

2. Sep 8, 20082008 NVO Summer School2 Motivation and Requirements A correct image WCS is fundamental to a lot of VO processing (e.g. Catalog generation and X-match, data quality). So,a service is needed that –Given an image with a poor WCS, will improve it; –Given an image with no WCS, will find one; –Given an image with a non-standard WCS, will standardize it (e.g. DSS plate solutions) Must run from a web-browser and return the corrected image Provides good feedback to the user about what was done and the quality of the solution

3. Sep 8, 20082008 NVO Summer School3 Design Goals NGC3104 Interactive interface Single-page display Exploit IRAF capabilities More than a simple web- based form Should be fun to write

4. Sep 8, 20082008 NVO Summer School4 DEMO

5. Sep 8, 20082008 NVO Summer School5 Technology Used SOA – AJAX

6. Sep 8, 20082008 NVO Summer School6 Technology Used SOA – AJAX (Simple, Only Apparently AJAX)

7. Sep 8, 20082008 NVO Summer School7 Technology Used SOA – AJAX (Simple, Only Apparently AJAX) IRAF/CL scripts for plate solution/graphics (~15 separate tasks) HTTP/POST service C-shell CGI script for form processing HTML iframes for layout CSS and Javascript for style/dynamic content Embedded Javascript in return stream for driving the user interface

8. Sep 8, 20082008 NVO Summer School8 Algorithm Verify image is valid (2-D, not an MEF, etc) Set initial conditions from user input or image header Generate reference catalog of what should be in the field Generate a catalog of detected objects in the image Cross-match the two catalogs (triangle algorithm, N brightest objects used) If (no solution found) {iterate by searching param space (e.g. No clipping) } else { compute plate solutionupdate image, data products }

9. Sep 8, 20082008 NVO Summer School9 Why Doesn't it Always Work? Too many points Not enough points Scale problems lead to bogus solution Selection Effect Image Geometry

10. Sep 8, 20082008 NVO Summer School10 Other Astrometry Engines Astrometry.net –Downloadable software –Image formats supported –No starting info required SCAMP - WCS solutions from SExtractor catalogs http://terapix.iap.fr Automatch - John Thorstensens tools http://mdm.kpno.noao.edu/Manuals/automatc h.html Pitt WCS Fixer http://nvogre.phyast.pitt.edu/wcs/

11. Sep 8, 20082008 NVO Summer School11 Future Work (Maybe) Web-Service interface Return reference/image catalogs (VOTable) Process multiple images (SIAP query table input instead of single image) Desktop application via VO Client Automatically explore parameter space

12. Sep 8, 20082008 NVO Summer School12