Aligning noteheads horizontally
The noteheadOrigin point is defined for noteheads with non-zero left-hand side bearings, such as the double whole (breve) notehead that has two vertical lines at either side of the oval notehead itself, as illustrated in the figure below:
The horizontal grey lines denote staff lines, for scale.
The light blue boxes show glyph bounding boxes, with the left-hand side of the box corresponding to x=0.
The vertical dashed grey lines denote the left-hand edge of the rhythmic position, i.e. the position against which the notehead is aligned.
The red box shows the location of the noteheadOrigin point, as specified in the font metadata JSON file.
The left-hand example shows the alignment that will be produced simply by positioning notehead glyphs using the left-hand edges of their bounding boxes. The right-hand example shows the superior alignment that can be produced by offsetting the double whole (breve) note leftwards by the distance between x=0 and the noteheadOrigin point.