Comments (4)
works for me
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Can't the user just say (int(x), int(y)) to centre in a pixel?
Yes, that is the current workaround.
im = psf.draw(x=int(x+0.5), y=int(y+0.5))
But it feels slightly clunky compared to
im = psf.draw(x,y, center=True)
I don't understand the
center=pos
option.
Well, you might not want the image you are drawing onto to have the same meanings of (x,y) as the original image where the interpolation is defined. For instance, you might have the image on which you are rendering the PSF be centered at (0,0) for convenience of some measuring code. Furthermore, you might be concerned about some pixelization effects in your code, so maybe you don't always want the PSF centered in the center of the central pixel. Maybe you want to dither around by a random sub-pixel offset relative to the center. Then you would do
cenx, ceny = np.random.rand(2) - 0.5
center = galsim.PositionD(cenx,ceny)
psf.draw(x,y, image=target_image, center=center)
measure_psf(target_image, center=center)
Anyway, if you don't have a use for it yourself, you don't need to use it (natch). But in some DES work we've been doing, there was some confusion on how Piff was working here, so this is intended to make it easier for the user to be clear about what they are asking Piff to do wrt the center of the rendering.
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FYI, I'll mostly be leveraging the work I did on this GalSim PR where I added a center
parameter to the drawImage
command. This will encompass how the center=pos
option will work. The other two options described above will just define two reasonable values for what that pos might be.
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Related Issues (20)
- Added functions need by optatmo to the util.py HOT 8
- Add a normalization option HOT 8
- Add calculate_moments function to util and associated unit tests. HOT 1
- PSF wings HOT 2
- Reading WCS solution of ZTF images HOT 1
- Stars Center on the stamps HOT 7
- psf.draw | wcs is not a list for single chip fit HOT 5
- Add equality testing HOT 1
- very large PSF (after re-installation) | Bad fit HOT 6
- regularize in a hacky way HOT 3
- Examples in documentation & `examples/` fail for v1.2 HOT 3
- Piff catastrophically fails when PixelGrid size is larger than input star images HOT 3
- Inconsistent piff log message levels HOT 2
- Fix max_snr weight adjustment.
- Make it easy to run just the star selection without fitting a PSF model
- incorrect error message with missing keyword
- coadd_object_id in psf_stars extension is stored as an f8 instead of an i8 HOT 3
- Add optional high order moments to the HSM output file. HOT 4
- Let weight, badpix be different files from image.
- Strange PSF fitting HOT 5
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