Spiral profile #1277
Spiral profile #1277
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The spiral is a lograthmic spiral in 3d that is projected onto 2d. The profile is represented by a number of point sources. The number of arms, inclination, rotation and hlr/disk height are configurable, as well as the pitch angle of the arms. Unit tests are also added in tests/test_spiral.py
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Cool! Would you still add a bulge component separately? |
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Yes, that can be added separately. In the color images above, the galaxies have up to three parts
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Here you can see the knots clearly |
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This is quite cool, Erin! The images look great. |
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Some things for discussion
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Thanks Erin - this is super cool. I was going to ask about computational expense and then you commented on it yourself... it feels to me like there must be some trick one could use, relying on the fact that each point is fundamentally the same exact light profile after PSF convolution, modulo sub-pixel shifts. (I assume we are still making the approximation that there is a single well-defined PSF for the entire |
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| self._orig_rng = rng.duplicate() | ||
| self._rng = rng | ||
| self._np_rng = np.random.default_rng(self._rng.raw()) |
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Better would be self._np.rng = self._rng.np.
cf. http://galsim-developers.github.io/GalSim/_build/html/deviate.html#galsim.BaseDeviate.as_numpy_generator
Or just use self._rng.np whenever you want np.random functions.
| from .position import PositionD | ||
| from coord import degrees, radians | ||
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| GOLDEN_SPIRAL_PITCH = 17.03239 |
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This deserves a comment giving the source.
# = arctan(ln(phi) / (pi/2))
# cf. https://en.wikipedia.org/wiki/Golden_spiral
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I'd also prefer this be a class value in SpiralParticles, rather than a module level constant.
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| GOLDEN_SPIRAL_PITCH = 17.03239 | ||
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| PIXEL_SCALE = 0.2 |
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I think you don't use this. Which is good, since this shouldn't be hard-coded.
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| @doc_inherit | ||
| def magnify(self, scale): | ||
| return self.expand(scale) |
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This is wrong. It should be expand(mu**0.5). (Where mu is what we normally call the arg here.) Probably should just omit this override though.
| def withFlux(self, flux): | ||
| kw = self._get_constructor_kw() | ||
| kw['flux'] = flux | ||
| return Spiral(**kw) |
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Not sure if this one is necessary or helpful. Rescaling the flux value isn't slow in k-space. (Probably isn't helpful for RandomKnots either.)
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| def _sample_exponential(rng, r0, n): | ||
| return rng.exponential( | ||
| scale=r0 * 2.375, |
| np.testing.assert_almost_equal(sp.centroid.y, pts[:, 1].mean()) | ||
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| sp.calculateHLR() | ||
| sp.calculate_e1e2() |
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Should probably assert something about the return values of these two, rather than just that they run without error.
| conv2 = galsim.Convolve(sp2, psf) | ||
| im1 = conv1.drawImage() | ||
| im2 = conv2.drawImage() | ||
| assert im1 == im2 |
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I guess this is asserting that xvalue_accuracy and kvalue_accuracy are not used by the Spiral class anywhere. Seems more useful to test that something that does matter causes the image to be different.
| # Check that image is not sensitive to use of rng by other objects. | ||
| rng3 = galsim.BaseDeviate(seed) | ||
| sp3 = galsim.Spiral(npoints, half_light_radius=hlr, rng=rng3) | ||
| rng3.discard(523) |
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I'm not sure this is an interesting test. I think the rng is only used by the constructor. Once the points are made, even if the rng wasn't duplicated, I think this would still work. Perhaps a better test that you are sequestering the rng would be that copying it still produces the same image.
rng3.discard(523)
sp4 = sp3.withFlux(sp3.flux)
sp5 = sp3.copy()
sp6 = sp3.shift(0,0)
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These should all be equivalent to sp3, and I think exercise the step of duplicating the rng.
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| check_pickle(sp, irreprable=True) | ||
| check_pickle(conv1, irreprable=True) | ||
| check_pickle(conv1, lambda x: x.drawImage(scale=1), irreprable=True) |
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I'd like these to all work with irrerable=False.
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Hi @esheldon - thanks have been quiet on this PR for a while, so I wanted to check in and let you know that we've been discussing tagging GalSim v2.6 in about a month from now. Do you want this feature in the next tagged version, and if so, do you anticipate that timeline working for you to address the review? |
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I started this as a fun project with my son while on vacation. I haven't had any time since to work on it. If I don't get to Mike's comments in time, please don't wait for me. |
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Ah, the vacation project; I can relate to that phenomenon. Thanks for letting us know... we won't wait on this, but if you do find time for it, we can definitely include it. |
Adds a new profile
Spiralthat creates a logarithmic spiral object, represented by point sources.The points are created in three dimensions in a disk, with possible inclination along the line of sight and rotations in the plane of the sky. The number of spiral arms is also configurable.
Some examples
two spiral arms
Points in 3d as well as a rendered image
Edge on
More arms
Full scenes