NEW: functions to pass from pixel coordinates to physical and from physical to pixel coordinates
NEW: functions to pass from pixel coordinates to physical and from physical to pixel coordinates

Former-commit-id: 67fa2326e8a58b075846cfce170e94308a26d4e0
Former-commit-id: 6dfbefdc0aef6cfad1e7edd5c81cfeb6f301e6fb
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox