added _bg_index_to_camera_index, #41

psgeom/camera.py

@@ -220,6 +220,55 @@ def to_hdf5(self, filename):
 
     def from_hdf5(self, filename):
         raise NotImplementedError()
+
+
+    def _bg_index_to_camera_index(self, bg_index):
+        """
+        Map a basisgrid panel index to a tuple of "camera" indices:
+
+           (leaf_index, subpanel_index)
+
+        This allows one to map "backwards" from a basisgrid to a
+        specific subpanel. For example, a JUNGFRAU sensor element
+        is composed of a 4x2 array of subpanels that each become
+        their own basisgrid elements. Each subpanel will belong
+        to the same "leaf" but have a unique subpanel index.
+
+        Subpanel indices go in slow/fast order as might be expected.
+
+        The leaf index gives the position of the basisgrid panel
+        in CompoundAreaCamrea.leaves
+
+        Parameters
+        ----------
+        bg_index : int
+            An index of the basisgrid that would be generated from
+            CompoundAreaCamera.to_basisgrid() 
+
+        Returns
+        -------
+        camera_index : tuple of ints
+            (leaf_index, subpanel_index)
+        """
+
+        # just count subpanels until we reach "bg_index" number of subpanels
+
+        subpanels_per_leaf = [ np.product(l.subpanel_shape) for l in self.leaves ]
+
+        if bg_index >= np.sum(subpanels_per_leaf):
+            raise ValueError('bg_index requested: %d, but Camera only has %d subpanels'
+                             '' % (bg_index, np.sum(subpanels_per_leaf)))
+
+        c = 0
+        for leaf_index, n_panels in enumerate(subpanels_per_leaf):
+            c += n_panels
+
+            if c > bg_index: # the bg_index is in this leaf
+                subpanels_before_this_leaf = c - n_panels
+                subpanel_index = bg_index - subpanels_before_this_leaf
+                break
+
+        return (leaf_index, subpanel_index)
 
 
     def to_basisgrid(self):

test/test_camera.py

@@ -103,7 +103,17 @@ def test_jungfrau_vs_geometry_access(self):
 
         assert err < 10.0, 'error greater than 10um avg per px (%f)' % err
         assert num_more_than_1px_err < 7500, '>7500 pix w err > 1 px'
+
+
+    def test_bg_index_to_camera_index(self):
+        # we have a cspad 2M: 4x4=16 leaves, 2 subpanels/leaf
 
+        assert self.geom._bg_index_to_camera_index(0)  == (0,0)
+        assert self.geom._bg_index_to_camera_index(1)  == (0,1)
+        assert self.geom._bg_index_to_camera_index(2)  == (1,0)
+        assert self.geom._bg_index_to_camera_index(3)  == (1,1)
+        assert self.geom._bg_index_to_camera_index(31) == (15,1)
+
 
 class TestCspad:
 
@@ -153,8 +163,8 @@ def test_hdf5_file(self):
         xyz2 = np.array(f['/xyz'])
         f.close()
 
-		# we re-shape the xyz to match the way psana
-		# presents CSPAD data
+        # we re-shape the xyz to match the way psana
+        # presents CSPAD data
         assert xyz2.shape == self.geom.xyz.shape
         np.testing.assert_allclose(self.geom.xyz, xyz2)
 
@@ -167,6 +177,15 @@ def setup(self):
 
         self.geom = camera.CompoundAreaCamera.from_psana_file('ref_files/jungfrau/jungfrau4m.data')
         self.klass = camera.CompoundAreaCamera
+
+    def test_bg_index_to_camera_index(self):
+        # we have a JF 4M: 4x2=8 leaves, 8 subpanels/leaf
+
+        for i in range(8):
+            assert self.geom._bg_index_to_camera_index(i) == (0,i)
+        assert self.geom._bg_index_to_camera_index(8)  == (1,0)
+        assert self.geom._bg_index_to_camera_index(63) == (7,7)
+
 
     def test_to_basis_grid(self):