Patricia Shanahan wrote:
D-Dog wrote:
Hi,
I have a polar plot graph plotted on a JPanel, and I would like to
determine the angle selected around that graph, given the x,y position
of the mouse. I know this is probably more of a math (trig) question,
but I figured I would check here first, as I'm sure someone has dealt
with this before. I know how to retrieve the x,y position given the
radius, center_point, and angle, just not how to do the reverse of
that.
I've never done this in Java graphics, so I don't know if there is any
graphics-specific method. On general trig principles, if the center
point is at (x1,y1), I would use Math.atan2(y-y1,x-x1).
In the graphics libraries, e.g.,
<http://java.sun.com/javase/6/docs/api/java/awt/Graphics2D.html>
, the sign of y is reversed.
This default transform maps the user space coordinate system to screen
and printer device coordinates such that the origin maps to the upper
left hand corner of the target region of the device with increasing X
coordinates extending to the right and increasing Y coordinates
extending downward.
Very good point. If the OP uses something like -r*Math.sin(theta) to get