added method to plot surface componenets of mixed source estimate
added tests for mixed spaces. added method to export volume source estimates to nifti
finally got rid of that extra transform by adding a transpose, similar to what source_estimate.py does
added option to export surface estimate data to nifti
fixes from last pull request
updated docstrings, added support to write to .mgz file
expanding method to export SourceSpaces to volume. Now supports surfaces and volumes, mri_resolution (volume only), .mgz and .nii files
added options for mri_resolution, however surface is still failing
modified vertex_to_mri to use transformation conventions
Added exporting discrete sources. Added ability to rotate from head coordinates. Added comments for coordinate frames. Switched high res for volumes so that it actually reads aseg file again (otherwise it looked boxy).
added tests for export_volume
added coordinate frame to SourceSpaces.__repr__
expanded comments on transformations in forward. addressed agramfort's comments from 2014-08-08.
addressed comments from over the weekend
moved tests for export_volume to forward, since this is where source spaces are in head coordinates. fixed defaults in source_space
updated example to work with latest code. used smaller source spaces to speed up tests
reverted to original way of generating mri grid since its faster than mgrid
removed save as volume function from mixed source space (to be addressed in next PR). modified SourceSpaces.export_volume to do away with usage of _compute_nearest
fixed indexing to use round, not float. also implemented clipping for voxels outside of source space
added warnings for surface and discrete vertices that lay outside of volume source space