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

Sep 8, 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

Sep 8, 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

Sep 8, NVO Summer School4 DEMO

Sep 8, NVO Summer School5 Technology Used SOA – AJAX

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

Sep 8, 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

Sep 8, 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 }

Sep 8, 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

Sep 8, NVO Summer School10 Other Astrometry Engines Astrometry.net –Downloadable software –Image formats supported –No starting info required SCAMP - WCS solutions from SExtractor catalogs Automatch - John Thorstensens tools h.html Pitt WCS Fixer

Sep 8, 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

Sep 8, NVO Summer School12