Thee mutually perpendicular lines in space define three mutually perpendicular planes which in turn divide the space into eight parts known as octants and the lines are known as the coordinate axes.
(x,y,z), the coordinates of a point P are the perpendicular distances from P on the three mutually rectangular coordinate planes YOZ, ZOX, and XOY respectively. The coordinates of a point are the distances from the origin of the feet of the perpendiculars from the point on the respective coordinate axes.
Sign convention of three dimensional geometry
All distances measured along OX, OY, and OZ will be positive.
All distances measured along or parallel to OX’, OY’, Oz’ will be negative.