I am trying to recover the PSFs created by processCcd or singleFrameDriver. I can see the PSFex outputs are stored in extensions 15 and 16 binary tables. Specifically, it seems the basis functions are in extension 16, table extension 5, with coefficients in table extension 2, and the psf shape in table extension 4. Great.
What I can’t figure out from the limited PSFex documentation i can find, is what is the functional form of the PSF from its basis functions? For example, is it a linear sum of the form:
PSF = c_1basis_1 + c_2basis_2 + …
or a power series:
PSF = c_1basis_1^1 + c_2basis_2^2 + …
or something else?
FWIW the power series produces something reasonable looking. But can’t be sure it’s correct.