TractAngleMap[tracts,vox,dim]

makes a tract angle map based on the tracts angles with the z-plane.

TractAngleMap[tracts,v1,vox,dim]

makes a tract angle map based on the tracts angles with the plane normal to v1.

TractAngleMap[tracts,{v1,v2},vox,dim]

makes a tract angle map based on the tracts elevation angles with the plane normal to v1 and the azimuth angle in that plane relative to v2.