Merge pull request #4255 from eteq/change-gcrs-itrs-cirs

eteq · eteq · commit e9b2cca282d6 · 2015-11-09T02:02:28.000-08:00
Change ordering of GCRS/ITRS transforms to make more sense
diff --git a/CHANGES.rst b/CHANGES.rst
@@ -1,3 +1,163 @@
+1.2 (unreleased)
+----------------
+
+New Features
+^^^^^^^^^^^^
+
+- ``astropy.analytic_functions``
+
+- ``astropy.config``
+
+- ``astropy.conftest.py``
+
+- ``astropy.constants``
+
+- ``astropy.convolution``
+
+- ``astropy.coordinates``
+
+- ``astropy.cosmology``
+
+- ``astropy.io.ascii``
+
+- ``astropy.io.fits``
+
+- ``astropy.io.misc``
+
+- ``astropy.io.votable``
+
+- ``astropy.logger.py``
+
+- ``astropy.modeling``
+
+- ``astropy.nddata``
+
+- ``astropy.stats``
+
+- ``astropy.table``
+
+- ``astropy.tests``
+
+- ``astropy.time``
+
+- ``astropy.units``
+
+- ``astropy.utils``
+
+- ``astropy.visualization``
+
+- ``astropy.vo``
+
+- ``astropy.wcs``
+
+API changes
+^^^^^^^^^^^
+
+- ``astropy.analytic_functions``
+
+- ``astropy.config``
+
+- ``astropy.conftest.py``
+
+- ``astropy.constants``
+
+- ``astropy.convolution``
+
+- ``astropy.coordinates``
+
+- ``astropy.cosmology``
+
+- ``astropy.io.ascii``
+
+- ``astropy.io.fits``
+
+- ``astropy.io.misc``
+
+- ``astropy.io.votable``
+
+- ``astropy.logger.py``
+
+- ``astropy.modeling``
+
+- ``astropy.nddata``
+
+- ``astropy.stats``
+
+- ``astropy.table``
+
+- ``astropy.tests``
+
+- ``astropy.time``
+
+- ``astropy.units``
+
+- ``astropy.utils``
+
+- ``astropy.visualization``
+
+- ``astropy.vo``
+
+- ``astropy.wcs``
+
+Bug fixes
+^^^^^^^^^
+
+- ``astropy.analytic_functions``
+
+- ``astropy.config``
+
+- ``astropy.conftest.py``
+
+- ``astropy.constants``
+
+- ``astropy.convolution``
+
+- ``astropy.coordinates``
+
+- ``astropy.cosmology``
+
+- ``astropy.io.ascii``
+
+- ``astropy.io.fits``
+
+- ``astropy.io.misc``
+
+- ``astropy.io.votable``
+
+- ``astropy.logger.py``
+
+- ``astropy.modeling``
+
+- ``astropy.nddata``
+
+- ``astropy.stats``
+
+- ``astropy.table``
+
+- ``astropy.tests``
+
+- ``astropy.time``
+
+- ``astropy.units``
+
+- ``astropy.utils``
+
+- ``astropy.visualization``
+
+- ``astropy.vo``
+
+- ``astropy.wcs``
+
+Other Changes and Additions
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+- In ``astropy.coordinates``, the transformations between GCRS, CIRS,
+  and ITRS have been adjusted to more logically reflect the order in
+  which they actually apply.  This should not affect most coordinate
+  transformations, but may affect code that is especially sensitive to
+  machine precision effects that change when the order in which
+  transformations occur is changed. [#4255]
+
 1.1 (unreleased)
 ----------------
 
diff --git a/astropy/coordinates/builtin_frames/intermediate_rotation_transforms.py b/astropy/coordinates/builtin_frames/intermediate_rotation_transforms.py
@@ -20,21 +20,10 @@
 from .itrs import ITRS
 from .utils import get_polar_motion
 
-# first define helper functions
-def gcrs_to_itrs_mat(time):
-    #first compute the celestial-to-intermediate matrix
-    c2imat = erfa.c2i06a(time.jd1, time.jd2)
-
-    #now compute the polar motion p-matrix
-    xp, yp = get_polar_motion(time)
-    sp = erfa.sp00(time.jd1, time.jd2)
-    pmmat = erfa.pom00(xp, yp, sp)
-
-    #now determine the Earth Rotation Angle for the input obstime
-    era = erfa.era00(time.jd1, time.jd2)
-
-    return erfa.c2tcio(c2imat, era, pmmat)
-
+# # first define helper functions
+def gcrs_to_cirs_mat(time):
+    #felestial-to-intermediate matrix
+    return erfa.c2i06a(time.jd1, time.jd2)
 
 def cirs_to_itrs_mat(time):
     #compute the polar motion p-matrix
@@ -56,25 +45,23 @@ def gcrs_precession_mat(equinox):
 
 # now the actual transforms
 
-# the priority for the GCRS<->ITRS transforms are higher (=less traveled) to
-#make GCRS<->ICRS<->CIRS the preferred route over GCRS<->ITRS<->CIRS
-@frame_transform_graph.transform(FunctionTransform, GCRS, ITRS, priority=1.01)
-def gcrs_to_itrs(gcrs_coo, itrs_frame):
+@frame_transform_graph.transform(FunctionTransform, GCRS, CIRS)
+def gcrs_to_cirs(gcrs_coo, cirs_frame):
     # first get us to a 0 pos/vel GCRS at the target obstime
-    gcrs_coo2 = gcrs_coo.transform_to(GCRS(obstime=itrs_frame.obstime))
+    gcrs_coo2 = gcrs_coo.transform_to(GCRS(obstime=cirs_frame.obstime))
 
     #now get the pmatrix
-    pmat = gcrs_to_itrs_mat(itrs_frame.obstime)
+    pmat = gcrs_to_cirs_mat(cirs_frame.obstime)
     crepr = cartrepr_from_matmul(pmat, gcrs_coo2)
-    return itrs_frame.realize_frame(crepr)
+    return cirs_frame.realize_frame(crepr)
 
 
-@frame_transform_graph.transform(FunctionTransform, ITRS, GCRS, priority=1.01)
-def itrs_to_gcrs(itrs_coo, gcrs_frame):
+@frame_transform_graph.transform(FunctionTransform, CIRS, GCRS)
+def cirs_to_gcrs(cirs_coo, gcrs_frame):
     #compute the pmatrix, and then multiply by its transpose
-    pmat = gcrs_to_itrs_mat(itrs_coo.obstime)
-    newrepr = cartrepr_from_matmul(pmat, itrs_coo, transpose=True)
-    gcrs = GCRS(newrepr, obstime=itrs_coo.obstime)
+    pmat = gcrs_to_cirs_mat(cirs_coo.obstime)
+    newrepr = cartrepr_from_matmul(pmat, cirs_coo, transpose=True)
+    gcrs = GCRS(newrepr, obstime=cirs_coo.obstime)
 
     #now do any needed offsets (no-op if same obstime and 0 pos/vel)
     return gcrs.transform_to(gcrs_frame)
