Line
Builds the line (gx, gy, gz), unitized and zero-sanitized.
A g-part whose weight ‖(gx, gy)‖ doesn't round to zero is divided out to the unit normal, leaving gz the origin's signed distance. A weight that rounds to zero at the SCALE quantum leaves the line at infinity, all three components kept raw: the magnitude gz is data. Signed zeroes sanitize to +0.0.
Parameters
gx
The e423 component: the normal's x-component.
gy
The e431 component: the normal's y-component.
gz
The e412 component: the offset term of gx·x + gy·y + gz = 0.