Evaluate the xi-lambda image with direct bilinear interpolation - #993
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Evaluate the xi-lambda image with direct bilinear interpolation#993astronomyk wants to merge 1 commit into
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map_spectra_to_focal_plane evaluates the XiLamImage at every pixel of the detector sub-image through RectBivariateSpline(kx=ky=1) with grid=False. FITPACK's scattered-point evaluation is orders of magnitude slower than a direct bilinear lookup on the regular (xi, lam) grid: for a METIS long-slit trace this one call took ~3 s per FieldOfView. XiLamImage.interp is now a method that performs the bilinear interpolation directly, with identical semantics (including clamping of out-of-range coordinates); the call site is unchanged. Adds equivalence tests against RectBivariateSpline for scattered and grid evaluation, including points beyond the grid edges. The full basic_instrument spectroscopy/ifu suite passes unchanged.
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What
map_spectra_to_focal_planeevaluates the rectified (xi, lambda) spectrum at every pixel of the detector sub-image throughRectBivariateSpline(kx=ky=1)withgrid=False. FITPACK's scattered-point evaluation path is very slow for large coordinate arrays: for a METIS long-slit trace this single call took ~3 s per FieldOfView.XiLamImage.interpis now a method performing the bilinear interpolation directly on the regular (xi, lambda) grid — identical semantics forkx=ky=1, including the clamping of out-of-range coordinates, for bothgrid=Falseandgrid=True. The call site is unchanged, and the spline attribute no longer needs to be built eagerly in the constructor.Measured on the rectified spectrum of a real METIS LSS observation: 3.77 s -> 1.46 s for 1.4M evaluation points (the isolated microbenchmark difference is considerably larger for bigger sub-images).
Testing
TestXiLamImage::test_interp_matches_rect_bivariate_spline— equivalence againstRectBivariateSplinefor scattered and grid evaluation, including points beyond the grid edges.Note: includes the same 3-line
MockCubeFov(data=...)test-helper extension as #989; the two merge cleanly in either order.