Add gsparams capabilities to demo7

(#365)

examples/demo7.py

@@ -43,6 +43,7 @@
 - dev = galsim.PoissonDeviate(rng, mean)
 = noise = galsim.DeviateNoise(dev)
 - writeCube(..., compress='gzip')
+- gsparams = galsim.GSParams(...)
 """
 
 import sys
@@ -91,29 +92,60 @@ def main(argv):
 
     psf_fwhm = 0.65         # arcsec
 
+    # This script is set up as a comparison between using FFTs for doing the convolutions and
+    # shooting photons.  The two methods have trade-offs in speed and accuracy which vary
+    # with the kind of profile being drawn and the S/N of the object, among other factors.
+    # In addition, for each method, there are a number of parameters GalSim uses that control 
+    # aspects of the calculation that further affect the speed and accuracy.  
+    #
+    # We encapsulate these parameters with an object called GSParams.  The default values
+    # are intended to be accurate enough for normal precision shear tests, without sacrificing
+    # too much speed.  
+    #
+    # Any PSF or galaxy object can be given a gsparams argument on construction that can 
+    # have different values to make the calculation more or less accurate (typically trading
+    # off for speed or memory).  
+    #
+    # In this script, we adjust some of the values slightly, just to show you how it works.
+    # You could play around with these values and see what effect they have on the drawn images.
+    # Usually, it requires a pretty drastic change in these parameters for you to be able to 
+    # notice the difference by eye.  But subtle effects that may impact the shapes of galaxies
+    # can happen well before then.
+
+    # Type help(galsim.GSParams) for the complete list of parameters and more detailed docs.
+    gsparams = galsim.GSParams(
+        alias_threshold=1.e-2,   # maximum fractionalr flux that may be aliased around edge of FFT
+        maxk_threshold=2.e-3,    # k-values less than this may be excluded off edge of FFT
+        xvalue_accuracy=1.e-4,   # approximations in real space aim to be this accurate
+        kvalue_accuracy=1.e-4,   # approximations in fourier space aim to be this accurate
+        shoot_accuracy=1.e-4,    # approximations in photon shooting aim to be this accurate
+        minimum_fft_size=64)     # minimum size of ffts
+
     logger.info('Starting demo script 7')
 
     # Make the pixel:
     pix = galsim.Pixel(xw = pixel_scale)
 
     # Make the PSF profiles:
-    psf1 = galsim.Gaussian(fwhm = psf_fwhm)
-    psf2 = galsim.Moffat(fwhm = psf_fwhm, beta = 2.4)
-    psf3_inner = galsim.Gaussian(fwhm = psf_fwhm, flux = 0.8)
-    psf3_outer = galsim.Gaussian(fwhm = 2*psf_fwhm, flux = 0.2)
+    psf1 = galsim.Gaussian(fwhm = psf_fwhm, gsparams=gsparams)
+    psf2 = galsim.Moffat(fwhm = psf_fwhm, beta = 2.4, gsparams=gsparams)
+    psf3_inner = galsim.Gaussian(fwhm = psf_fwhm, flux = 0.8, gsparams=gsparams)
+    psf3_outer = galsim.Gaussian(fwhm = 2*psf_fwhm, flux = 0.2, gsparams=gsparams)
     psf3 = psf3_inner + psf3_outer
-    atmos = galsim.Gaussian(fwhm = psf_fwhm)
+    atmos = galsim.Gaussian(fwhm = psf_fwhm, gsparams=gsparams)
     optics = galsim.OpticalPSF(
             lam_over_diam = 0.6 * psf_fwhm,
             obscuration = 0.4,
             defocus = 0.1,
             astig1 = 0.3, astig2 = -0.2,
             coma1 = 0.2, coma2 = 0.1,
-            spher = -0.3) 
-    psf4 = galsim.Convolve([atmos,optics])
+            spher = -0.3, gsparams=gsparams) 
+    psf4 = galsim.Convolve([atmos,optics])  # Convolve inherits the gsparams from the first 
+                                            # item in the list.  (Or you can supply a gsparams
+                                            # argument explicitly if you want to override this.
     #atmos = galsim.AtmosphericPSF(fwhm = psf_fwhm)
-    atmos = galsim.Kolmogorov(fwhm = psf_fwhm)
-    optics = galsim.Airy(lam_over_diam = 0.3 * psf_fwhm) 
+    atmos = galsim.Kolmogorov(fwhm = psf_fwhm, gsparams=gsparams)
+    optics = galsim.Airy(lam_over_diam = 0.3 * psf_fwhm, gsparams=gsparams) 
     psf5 = galsim.Convolve([atmos,optics])
     psfs = [psf1, psf2, psf3, psf4, psf5]
     psf_names = ["Gaussian", "Moffat", "Double Gaussian", "OpticalPSF", "Kolmogorov * Airy"]
@@ -122,12 +154,12 @@ def main(argv):
     psf_phot_times = [0,0,0,0,0]
 
     # Make the galaxy profiles:
-    gal1 = galsim.Gaussian(half_light_radius = 1)
-    gal2 = galsim.Exponential(half_light_radius = 1)
-    gal3 = galsim.DeVaucouleurs(half_light_radius = 1)
-    gal4 = galsim.Sersic(half_light_radius = 1, n = 2.5)
-    bulge = galsim.Sersic(half_light_radius = 0.7, n = 3.2)
-    disk = galsim.Sersic(half_light_radius = 1.2, n = 1.5)
+    gal1 = galsim.Gaussian(half_light_radius = 1, gsparams=gsparams)
+    gal2 = galsim.Exponential(half_light_radius = 1, gsparams=gsparams)
+    gal3 = galsim.DeVaucouleurs(half_light_radius = 1, gsparams=gsparams)
+    gal4 = galsim.Sersic(half_light_radius = 1, n = 2.5, gsparams=gsparams)
+    bulge = galsim.Sersic(half_light_radius = 0.7, n = 3.2, gsparams=gsparams)
+    disk = galsim.Sersic(half_light_radius = 1.2, n = 1.5, gsparams=gsparams)
     gal5 = 0.4*bulge + 0.6*disk  # Net half-light radius is only approximate for this one.
     gals = [gal1, gal2, gal3, gal4, gal5]
     gal_names = ["Gaussian", "Exponential", "Devaucouleurs", "n=2.5 Sersic", "Bulge + Disk"]

examples/demo7.yaml

@@ -41,6 +41,7 @@
 # - image type : Tiled (..., stamp_size, xborder, yborder)
 # - image : draw_method (fft or phot)
 # - output : file_name with .gz, .bz2 or .fz extension automatically uses compression.
+# - image : gsparams
 
 
 # Define the PSF profiles
@@ -155,6 +156,26 @@ image :
     # two times, so the fft and phot images get the same values for the random parameters.
     random_seed : { type : Sequence , first : 553728 , repeat : 2 }
 
+    # This script is set up as a comparison between using FFTs for doing the convolutions and
+    # shooting photons.  The two methods have trade-offs in speed and accuracy which vary
+    # with the kind of profile being drawn and the S/N of the object, among other factors.
+    # In addition, for each method, there are a number of parameters GalSim uses that control 
+    # aspects of the calculation that further affect the speed and accuracy.  
+    #
+    # These parametsrs can be adjusted from the defaults with a gsparams item, either in
+    # image (in which case the values apply to all objects) or in the gal or psf layer 
+    # in which case the values apply to just that object.  For this script, we just apply a 
+    # global change to some of the values, just to demonstrate how it works.
+    # 
+    # See the config documentation for the complete list of parameters and more detailed 
+    # documentation.
+    gsparams :
+        alias_threshold : 1.0e-2   # maximum fractionalr flux that may be aliased around edge of FFT
+        maxk_threshold : 2.0e-3    # k-values less than this may be excluded off edge of FFT
+        xvalue_accuracy : 1.0e-4   # approximations in real space aim to be this accurate
+        kvalue_accuracy : 1.0e-4   # approximations in fourier space aim to be this accurate
+        shoot_accuracy : 1.0e-4    # approximations in photon shooting aim to be this accurate
+        minimum_fft_size : 64      # minimum size of ffts
 
 # Define the name and format of the output file
 output :

examples/json/demo7.json

@@ -23,6 +23,7 @@
 "#" : "- image type : Tiled (..., stamp_size, xborder, yborder)",
 "#" : "- image : draw_method (fft or phot)",
 "#" : "- output : file_name with .gz, .bz2 or .fz extension automatically uses compression.",
+"#" : "- image : gsparams",
 
 
 "#" : "Define the PSF profiles",
@@ -67,8 +68,8 @@
 
     "index" : {
         "type" : "Sequence",
-	"first" : 0,
-	"last" : 4,
+        "first" : 0,
+        "last" : 4,
 
         "#" : "How many times to repeat the same value before moving on:",
         "repeat" : 40 
@@ -149,7 +150,36 @@
     "#" : "The usual case is to just set a single number, which really means that each object",
     "#" : "gets a sequential value starting with this number.  In this case we repeat each value",
     "#" : "two times, so the fft and phot images get the same values for the random parameters.",
-    "random_seed" : { "type" : "Sequence" , "first" : 553728 , "repeat" : 2 }
+    "random_seed" : { "type" : "Sequence" , "first" : 553728 , "repeat" : 2 },
+
+    "#" : "This script is set up as a comparison between using FFTs for doing the convolutions and",
+    "#" : "shooting photons.  The two methods have trade-offs in speed and accuracy which vary",
+    "#" : "with the kind of profile being drawn and the S/N of the object, among other factors.",
+    "#" : "In addition, for each method, there are a number of parameters GalSim uses that control",
+    "#" : "aspects of the calculation that further affect the speed and accuracy.",
+
+    "#" : "These parametsrs can be adjusted from the defaults with a gsparams item, either in",
+    "#" : "image (in which case the values apply to all objects) or in the gal or psf layer",
+    "#" : "in which case the values apply to just that object.  For this script, we just apply a",
+    "#" : "global change to some of the values, just to demonstrate how it works.",
+
+    "#" : "See the config documentation for the complete list of parameters and more detailed",
+    "#" : "documentation.",
+    "gsparams" : {
+        "#" : "maximum fractionalr flux that may be aliased around edge of FFT",
+        "alias_threshold" : 1.0e-2,
+        "#" : "k-values less than this may be excluded off edge of FFT",
+        "maxk_threshold" : 2.0e-3,
+        "#" : "approximations in real space aim to be this accurate",
+        "xvalue_accuracy" : 1.0e-4,
+        "#" : "approximations in fourier space aim to be this accurate",
+        "kvalue_accuracy" : 1.0e-4,
+        "#" : "approximations in photon shooting aim to be this accurate",
+        "shoot_accuracy" : 1.0e-4,
+        "#" : "minimum size of ffts",
+        "minimum_fft_size" : 64
+    }
+
 },
 
 "#" : "Define the name and format of the output file",