问题
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?
回答1:
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: 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.
来源：https://stackoverflow.com/questions/30748651/how-should-i-interpret-the-coordinates-of-a-rectangle-in-pdf