Basics of Coordinate Metrology
Unit 2:  Coordinate systems - 2-D points

Step 4 of 5
  Next
       
This construction allows us to indicate the position of points in the form of numbers. Let us assume P is a point on the drawing plane. We then draw the distances to the two axes as shown in the diagram below (we place marks on the axis at a spacing of 1 to allow us to read the lengths more easily).

The two distances in this example are 3 and 2. Lets call the first number - i.e. 3 - the x coordinate and the second number - i.e. 2 - the y coordinate of the point P, written P(x,y), here: P(3, 2). These two numbers define the position of the point (relative to the axes). Strictly speaking, this method of determining the position only works if the point is on the right from the y axis and above the x axis. This is why we also have to admit negative coordinate values :
If a point is left from the y axis, its x coordinate value is the negative number of the distance from the y axis.
If a point is below the x axis, its y coordinate value is the negative number of the distance from the x axis.

     

   

  • Examples of points in coordinate systems