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NUMBER: 270 MODULE: imshift, magnify, xregister, geotran SYSTEM: V2.10 DATE: Fri Dec 9 10:48:34 MST 1994 FROM: davis BUG: Flux may not be conserved when the IMSHIFT, MAGNIFY, XREGISTER, or GEOTRAN tasks are run on undersampled data using the spline3 interpolant. In the worst case situation, completely undersampled data, fractional y shifts of 0.4-0.6, and placement near the top or bottom of the data buffer, the discrepancy is ~ +/- 0.3%. For well-sampled data the discrepancy is negligible. For y shifts which are exactly 0.0 there is no problem. The cause of the problem was that the number of edge lines being allocated for the spline3 buffers was too small for undersampled data and some of the power in the high frequency components of the interpolant was being lost. STATUS: Fixed for next release of iraf.
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