Add option to set a fixed dithering amount

.github/workflows/test.yml

@@ -34,10 +34,8 @@ jobs:
 
           conda config --set always_yes yes
 
-          conda install -q mamba==1.5.1
-
-          mamba install -q --file requirements.txt
-          mamba install -q \
+          conda install -q --file requirements.txt
+          conda install -q \
             flake8 \
             pytest \
             fitsio \

descwl_shear_sims/sim.py

@@ -65,6 +65,7 @@ def make_sim(
     draw_bright=True,
     psf_dim=51,
     dither=False,
+    dither_size=0.5,
     rotate=False,
     bands=["i"],
     epochs_per_band=1,
@@ -106,6 +107,12 @@ def make_sim(
         Dimensions of psf image.  Default 51
     dither: bool, optional
         Whether to dither the images at the pixel level, default False
+    dither_size: float, optional
+        The amplitude of dithering in unit of a fraction of a pixel
+        for testing pixel interpolation.
+        All SE WCS will be given random dithers with this amplitude in both image
+        x and y direction.
+        Value must be between 0 and 1.  default 0.5.
     rotate: bool, optional
         Whether to randomly rotate the image exposures randomly [not the
         rotation of intrinsic galaxies], default False
@@ -217,7 +224,6 @@ def make_sim(
             coadd_scale=coadd_scale,
             coadd_dim=coadd_dim,
             se_scale=pixel_scale,
-            dither=dither,
             rotate=rotate,
         )
 
@@ -275,6 +281,7 @@ def make_sim(
                 bright_mags=lists["bright_mags"],
                 coadd_bbox_cen_gs_skypos=coadd_bbox_cen_gs_skypos,
                 dither=dither,
+                dither_size=dither_size,
                 rotate=rotate,
                 mask_threshold=mask_threshold,
                 cosmic_rays=cosmic_rays,
@@ -355,6 +362,7 @@ def make_exp(
     bright_mags=None,
     coadd_bbox_cen_gs_skypos=None,
     dither=False,
+    dither_size=None,
     rotate=False,
     mask_threshold=None,
     cosmic_rays=False,
@@ -392,6 +400,11 @@ def make_exp(
         Dimensions of psf image that will be drawn when psf func is called
     dither: bool
         If set to True, dither randomly by a pixel width
+    dither_size: float, optional
+        The amplitude of dithering in unit of a fraction of a pixel
+        for testing pixel interpolation.
+        All se WCS will be dithered by this amount in both x and y directions.
+        Value must be between 0 and 1.  default None.
     rotate: bool
         If set to True, rotate the image exposure randomly, note, this is not
         the rotation of intrinsic galaxies in ring test
@@ -471,6 +484,7 @@ def make_exp(
             image_origin=se_origin,
             world_origin=coadd_bbox_cen_gs_skypos,
             dither=dither,
+            dither_size=dither_size,
             rotate=rotate,
             rng=rng,
         )
@@ -847,7 +861,7 @@ def get_sim_config(config=None):
 
 
 def get_se_dim(
-    *, coadd_dim, coadd_scale=None, se_scale=None, dither=False, rotate=False
+    *, coadd_dim, coadd_scale=None, se_scale=None, rotate=False
 ):
     """
     get single epoch (se) dimensions given coadd dim.
@@ -860,8 +874,6 @@ def get_se_dim(
         pixel scale of coadd
     se_scale: float, optional
         pixel scale of single exposure
-    dither: bool, optional
-        Whether there is dithering or not
     rotate: bool, optional
         Whether there are random rotations of image exposure or not
 

descwl_shear_sims/tests/test_sim.py

@@ -132,7 +132,6 @@ def test_sim_exp_mag(rotate, show=False):
     # use fixed single epoch dim so we can look in the same spot for the object
     se_dim = get_se_dim(
         coadd_dim=coadd_dim,
-        dither=False,
         rotate=True,
     )
 
@@ -204,7 +203,7 @@ def test_sim_psf_type(psf_type):
     )
 
     if psf_type == "ps":
-        se_dim = get_se_dim(coadd_dim=coadd_dim, dither=dither, rotate=rotate)
+        se_dim = get_se_dim(coadd_dim=coadd_dim, rotate=rotate)
         psf = make_ps_psf(rng=rng, dim=se_dim)
     else:
         psf = make_fixed_psf(psf_type=psf_type)

descwl_shear_sims/wcs/sewcs.py

@@ -11,6 +11,7 @@ def make_se_wcs(
     image_origin: galsim.PositionD,
     world_origin: galsim.CelestialCoord = WORLD_ORIGIN,
     dither: bool = False,
+    dither_size: float = None,
     rotate: bool = False,
     theta: float | None = None,
     rng=None,
@@ -29,6 +30,8 @@ def make_se_wcs(
         Origin on the sky
     dither: bool, optional
         whether to do dither or not, default: False
+    dither_size: float, optional
+        dither range in unit of a fraction of a pixel, default: None
     rotate: bool
         whether to do rotation or not, default: False
     theta: float
@@ -44,9 +47,10 @@ def make_se_wcs(
     if dither:
         # do a small offset of the origin
         assert rng is not None
-        dither_range = 0.5
-        off = rng.uniform(low=-dither_range, high=dither_range, size=2)
+
+        off = rng.uniform(low=-dither_size, high=dither_size, size=2)
         offset = galsim.PositionD(x=off[0], y=off[1])
+
         image_origin = image_origin + offset
 
     if rotate: