Cartesian Model, normal vector $\underline{n}=(a,b)$:
  1. $r=\left\{ (x,y)|~ax+by=c\right\}$;
  2. $H_1=\left\{ (x,y)|~ax+by \gt c\right\}$;
  3. $H_2=\left\{ (x,y)|~ax+by \lt c\right\}$;