An automatic method for determining COORDINATE TRANSFORMATIONS in FOCAS

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Session 28 -- Software and Catalogs
Display presentation, Tuesday, 31, 1994, 9:20-6:30

[28.05] An automatic method for determining COORDINATE TRANSFORMATIONS in FOCAS

Luis E. Campusano (Dpt.Astr., University of Chile, Santiago), Juan Vel\'asquez (Dpt.Computing Sc., University of Chile, Santiago), Francisco Valdes (NOAO), Peter B. Stetson (DAO)

An important new capability (program) has been added to the Faint Object Classification and Analysis System (FOCAS). Two FOCAS catalogs of objects produced from overlapping images, either in the same passband or different passbands, are compared and a coordinate system transformation from one set of image coordinates to another is automatically determined and applied to the object coordinates. The transformation is general and includes scale changes, rotations, and flips. The critical algorithm identifies a set of matching objects in the two catalogs. It consists of comparing all triangles formed from a subset of the objects in the two catalogs for similarity. These subsets in each catalog consist of the brightest objects to minimize the combinatoric size and effects of noise but with enough objects to overcome photometry differences, such as color effects, which produce different magnitude rankings. This list matching algorithm was previously proposed and implemented by Stetson in the DAOPHOT software. This poster describes the FOCAS program, the algorithms, and gives some examples.

The research of LEC and JV was supported in part by FONDECYT (Chile) grant No. 1930985.

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