Engine exhaust noise source is often described in frequency domain by the impedance and strength of an equivalent acoustic one-port source at a reference plane downstream of the exhaust manifold.
The bearing curve is the integral of the surface height histogram and plots the percentage of the surface above a reference plane as a function of the depth of that below the highest point of the image.
Taken as a reference plane at the time of measurement, the virtual plane was set so as to be a plane connecting the points of the largest bulge of the left/right maxillary tuberosities and the point of the incisive foramen, parallel to the Frankfort plane.
However, 3D analysis based on NHP as a reference plane is still controversial because of its sensitive reproducibility technologically and it is difficult to standardize [18].
Firstly, a reference plane (mostly a frontal cross section of the liver, prior to the stomach) has to be selected and fixed as an anchor.
Even for one-dimensional rough surfaces, depolarization occurs when the reference plane of incidence is not parallel to the local planes of incidence and scatter.
For these reasons, the ecliptic is used as the reference plane of the Solar System out of convenience.
This was in order to shift the minimum circle from the paper plane, which is the reference plane of the wavefront sensing, to the inside of phantom.
One reason for this is the lack of standardized, stable reference planes of the pelvis and an independent measurement method [ 18- 20].
The first full scale CMOS sensor was realised and equips the reference planes of the EUDET beam telescope.
