Fig. 1
![Fig. 1](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40902-016-0096-7/MediaObjects/40902_2016_96_Fig1_HTML.gif)
Horizontal reference plane (HRP) is PoRt-OrRt-PoLt, sagittal reference plane(SRP) is the plane perpendicular to horizontal reference plane including Na-Ba line, coronal plane is the plane perpendicular to horizontal and sagittal reference plane