Efficiently reproject partial sky maps (#170)

* [perf] reproj partial maps

- option to skip map pixels in ``ReprojectMaps``

* [doc] typo

* [fix] missing py binding

* [doc] line width

.gitignore

@@ -13,3 +13,4 @@ doc/module-autodocs.rst
 doc/moddoc_*
 *.g3
 .DS_Store
+.idea/

maps/python/map_modules.py

@@ -871,15 +871,27 @@ class ReprojectMaps(object):
     weighted : bool
         If True (default), ensure that maps have had weights applied before
         reprojection.  Otherwise, reproject maps without checking the weights.
+    partial :  bool=False
+        If True, the reproj will be performed on a partial map (of the output map),
+        defined by the mask. If the mask is not provided, it will be determined from
+        the non-zero pixels of the first reprojected map.
+    mask : G3SkyMapMask, G3SkyMap, or np.ndarray, Optional.
+        Mask to be used for partial reproject. This should be of the same size as the
+        output map. For numpy array, all zeros/inf/nan/hp.UNSEEN pixels are skipped.
     """
 
-    def __init__(self, map_stub=None, rebin=1, interp=False, weighted=True):
+    def __init__(self, map_stub=None, rebin=1, interp=False, weighted=True,
+                 partial=False, mask=None):
         assert map_stub is not None, "map_stub argument required"
         self.stub = map_stub.clone(False)
         self.stub.pol_type = None
         self.rebin = rebin
         self.interp = interp
         self.weighted = weighted
+        self._mask = None
+        self.partial = partial
+
+        self.mask = mask
 
     def __call__(self, frame):
         if isinstance(frame, core.G3Frame) and frame.type != core.G3FrameType.Map:
@@ -905,15 +917,48 @@ def __call__(self, frame):
 
             if key in "TQUH":
                 mnew = self.stub.clone(False)
-                maps.reproj_map(m, mnew, rebin=self.rebin, interp=self.interp)
+                maps.reproj_map(m, mnew, rebin=self.rebin, interp=self.interp,
+                                mask=self.mask)
 
             elif key in ["Wpol", "Wunpol"]:
                 mnew = maps.G3SkyMapWeights(self.stub)
                 for wkey in mnew.keys():
                     maps.reproj_map(
-                        m[wkey], mnew[wkey], rebin=self.rebin, interp=self.interp
+                        m[wkey], mnew[wkey], rebin=self.rebin, interp=self.interp,
+                        mask=self.mask
                     )
 
             frame[key] = mnew
-
+            self.mask = mnew
         return frame
+
+    @property
+    def mask(self):
+        return self._mask
+
+    @mask.setter
+    def mask(self, mask):
+        if mask is None:
+            return
+        if self._mask is None and self.partial:
+            if isinstance(mask, maps.G3SkyMapMask):
+                self._mask = mask
+            elif isinstance(mask, maps.G3SkyMap):
+                self._mask = maps.G3SkyMapMask(mask, use_data=True, zero_nans=True,
+                                               zero_infs=True)
+            elif isinstance(mask, np.ndarray):
+                from healpy import UNSEEN
+                tmp = self.stub.clone(False)
+                mask_copy = np.ones(mask.shape, dtype=int)
+                bad = np.logical_or.reduce([
+                    np.isnan(mask),
+                    np.isinf(mask),
+                    mask==0,
+                    mask==UNSEEN
+                ])
+                mask_copy[bad] = 0
+                tmp[:] = mask_copy
+                self._mask = maps.G3SkyMapMask(tmp, use_data=True)
+            else:
+                raise TypeError("Mask must be a G3SkyMapMask, G3SkyMap, "
+                                "or numpy array")

maps/src/maputils.cxx

@@ -279,7 +279,8 @@ void FlattenPol(FlatSkyMapPtr Q, FlatSkyMapPtr U, G3SkyMapWeightsPtr W, double h
 }
 
 
-void ReprojMap(G3SkyMapConstPtr in_map, G3SkyMapPtr out_map, int rebin, bool interp)
+void ReprojMap(G3SkyMapConstPtr in_map, G3SkyMapPtr out_map, int rebin, bool interp,
+				G3SkyMapMaskConstPtr out_map_mask)
 {
 	bool rotate = false; // no transform
 	Quat q_rot; // quaternion for rotating from output to input coordinate system
@@ -310,8 +311,13 @@ void ReprojMap(G3SkyMapConstPtr in_map, G3SkyMapPtr out_map, int rebin, bool int
 		out_map->pol_conv = in_map->pol_conv;
 	}
 
+	size_t stop = out_map->size();
 	if (rebin > 1) {
-		for (size_t i = 0; i < out_map->size(); i++) {
+		for (size_t i = 0; i < stop; i++) {
+			if (!!out_map_mask && !out_map_mask->at(i)) {
+				(*out_map)[i] = 0;
+				continue;
+			}
 			double val = 0;
 			auto quats = out_map->GetRebinQuats(i, rebin);
 			if (rotate)
@@ -328,7 +334,11 @@ void ReprojMap(G3SkyMapConstPtr in_map, G3SkyMapPtr out_map, int rebin, bool int
 			}
 		}
 	} else {
-		for (size_t i = 0; i < out_map->size(); i++) {
+		for (size_t i = 0; i < stop; i++) {
+			if (!!out_map_mask && !out_map_mask->at(i)) {
+				(*out_map)[i] = 0;
+				continue;
+			}
 			double val = 0;
 			auto q = out_map->PixelToQuat(i);
 			if (rotate)
@@ -572,15 +582,17 @@ PYBINDINGS("maps")
 		"the appropriate rotation to the Q and u elements of the associated weights.");
 
 	bp::def("reproj_map", ReprojMap,
-		(bp::arg("in_map"), bp::arg("out_map"), bp::arg("rebin")=1, bp::arg("interp")=false),
+		(bp::arg("in_map"), bp::arg("out_map"), bp::arg("rebin")=1, bp::arg("interp")=false,
+		bp::arg("mask")=bp::object()),
 		"Reprojects the data from in_map onto out_map.  out_map can have a different "
 		"projection, size, resolution, etc.  Optionally account for sub-pixel "
 		"structure by setting rebin > 1 and/or enable bilinear interpolation of "
 		"values from the input map by setting interp=True.  Use the maps' coord_ref "
 		"attributes to rotate between Equatorial and Galactic coordinate systems.  "
 		"Use the maps' pol_conv attributes to switch between COSMO and IAU "
 		"polarization conventions.  If output attributes are not set, they will be "
-		"copied from the input map.");
+		"copied from the input map. out_map_mask, if given, skip the unused pixels"
+		"and set these pixels to 0.");
 
 	bp::def("get_map_moments", GetMapMoments,
 		(bp::arg("map"), bp::arg("mask")=G3SkyMapMaskConstPtr(), bp::arg("order")=2,