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I would like to know more about the coordinates of a Rectangle, in particular:

- lower left X
- lower left Y
- upper right X
- upper right Y

Every time, I get confused about how to make dimensions based on these coordinates to draw rectangle. If possible, can I get a graphical representation briefly about these coordinates positions?

Posted on StackOverflow on Jun 10, 2015 by Nazeerbasha

Before someone can explain what the lower-left X, lower-left Y, upper-right X and upper-right Y of a rectangle are about, you need to know about the coordinate system as explained in the answer to the question "Where is the origin (x,y) of a PDF page?"

The answer to that question contains all the information you need, except for the graphical representation you are asking for. This is a simple representation of the coordinate system:

The origin of the coordinate system is `(0, 0)`

. Positive X values are to the right of the origin,
positive Y values are above the origin.

I have drawn a `Rectangle`

and indicates where you can find the lower-left corner (with coordinate `(llx, lly)`

)
and the upper-right corner (with coordinate `(urx, ury)`

).

The sides of the rectangle are always in parallel with the X and the Y axis, hence you only need two coordinates to define the rectangle.

**Important:**

All of the above assumes that you didn't introduce any coordinate transformations, e.g. using the `concatCTM()`

or `transform()`

method. These methods allow you to change the coordinate system, for instance change the angle between the x and y axis from 90 degrees (the default) to another angle. You can also scale an axis to get a different aspect ratio.