Qt Open GL Coordinate system

Hi,
Let's say I have two coordinate axis rendered correspondingly:
@
...
glBegin(GL_LINES);
//y
glVertex2f(1.5, 1.5);
glVertex2f(1.5, 1.5);
//y arrow
glVertex2f(1.5, 1.5);
glVertex2f(1.4, 1.4);glVertex2f(1.5, 1.5); glVertex2f(1.6, 1.4); glEnd();
...
@
@
...
glBegin(GL_LINES);
//x
glVertex2f(1.5, 1.5);
glVertex2f( 1.5, 1.5);
//x arrow
glVertex2f(1.5, 1.5);
glVertex2f(1.4, 1.4);glVertex2f(1.5, 1.5); glVertex2f(1.4, 1.6); glEnd();
...
@I also have a .csv file from which read the data and store it in a
@
QHash<QString, QVector<float> >
@.
Now I need to plot the points that I have read from the .csv file into my "coordinate system".Q: How to evaluate my coordinate system in that way (let's say from 0 to 20), that the points read would be plot in the coordinate system w.r.t. that values.
Example: The points read {2.4, 3.1}, {19.9, 1.7} must be plot w.r.t. to fact that the {0.0} is the crossroad of the axis (in my case {1.5, 1.5}), and the end points of my axis are correspondingly X  {20, 0} (in my case {1.5, 1.5}) and Y  {0, 20} (in my case {1.5, 1.5}).
P.S. : theoretically I know that it some how must be translating my world coordinate system into mine, but that's all that I know, and have no idea how it is done.
Thanks in advance.