Cleanup and add some comments

Author: hoechenberger

dipole_sim/transforms.py

@@ -4,20 +4,28 @@
 
 
 def gen_ras_to_head_trans(head_to_mri_t, t1_img):
-    mri_to_head_t = invert_transform(head_to_mri_t)
-
-    # RAS <> VOXEL
+    # RAS -> VOXEL
     ras_to_vox_t = Transform(fro='ras', to='mri_voxel',
                              trans=np.linalg.inv(t1_img.header.get_vox2ras()))
-    #  trans=t1_img.header.get_ras2vox())
+
+    # VOXEL -> MRI
     vox_to_mri_t = Transform(fro='mri_voxel', to='mri',
                              trans=t1_img.header.get_vox2ras_tkr())
 
-    # RAS <> MRI
+    # MRI -> HEAD
+    mri_to_head_t = invert_transform(head_to_mri_t)
+    
+    # Now we have generated all the required transformations
+    # to go from RAS to MNE Head coordinates. Let's combine
+    # the transforms into a single transform. This requires
+    # two calls to `combine_transforms()`.
+
+    # RAS -> MRI
     ras_to_mri_t = combine_transforms(ras_to_vox_t,
                                       vox_to_mri_t,
                                       fro='ras', to='mri')
 
+    # RAS -> HEAD
     ras_to_head_t = combine_transforms(ras_to_mri_t,
                                        mri_to_head_t,
                                        fro='ras', to='head')