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how OpenCV Java Detect ellipse, circle face in an image

Please, How we can use OpenCV Java , to detect an ellipse of face form in an image.
The code below is used for rectangular.
CvRect rect = new CvRect();
rect.x(100);
rect.y(100);
rect.width(200);
rect.height(200);
how can we make it ellipse or circle ?

Since you have a rect with pre-defined dimensions, you can simply use cv::circle(), to draw circles instead of rectangles on a given canvas.

Java 2D : Creating Shape Fixtures

I'm wondering if there is a way to create a shape fixture in Java 2D.
More specifically, I'm trying to be able to draw a predefined shape at different locations with different colors.
I know you can use the fill(shape) methods to draw shapes.
However, this seems to require creating a new shape at the coordinate that I want to draw it.
Is there any way to reuse the same shape each time? Or do I have to create a new shape for each location.

You can do this by translating the transformation matrix of the graphics object.
Let's say you have a Shape called shape whose coordinates are relative to the center of the Shape. You also have an instance of Graphics2D called g2.
Now you code could look something like this:
// Set the color of the Shape.
g2.setColor(Color.BLACK);
// Backup the transformation matrix so we can restore it later.
AffineTransform backupTransform = new AffineTransform(g2.getTransform());
// Translate everything that is drawn afterwards by the given coordinates.
// (This will be the new position of the center of the Shape)
g2.translate(53, 27);
// Draw the Shape.
g2.draw(shape);
// Restore the old transform, so that things drawn after this line
// are not affected by the translation.
g2.setTransform(backupTransform);

How can I rotate a Rectangle?

I'm attempting to rotate a Rectangle (the Java class) created with
Rectangle rect = new Rectangle(x, y, width, height);
I cannot appear to find anything in the API for it. If I google "Java rotate a rectangle", then I can only find threads telling me how to draw it rotated, and not just rotate the object.

AffineTransform.getRotateInstance(angle).createTransformedShape(rect) creates a Shape representing the rotated rectangle. (It can't return another Rectangle because Rectangle expects to just be straight along the x/y axes.)

Java AWT bounds

I have an assignment to draw a certain number of circles using java.awt.Graphics.
Drawing the circles is fairly simple, but I am only supposed to draw the circle if it appears within the visible area. I know I can call method getClipBounds() to determine the drawing area, but I'm having trouble finding a java implementation of a way to determine if a circle intersects a Rectangle.
Is that the right way to go about determining if the circle I want to draw will be completely visible or is there a simpler way?

Don't use the Graphics.fillOval(...) method to do the painting.
Instead you can use the Graphics2D.fill(Shape) method. You can create oval Shape objects using the Ellipse2D class.
but I'm having trouble finding a java implementation of a way to determine if a circle intersects a Rectangle.
The Shape object has a method that will allow you to get the rectangular bounds of the Shape. Then you can use the Rectangle.contains(...) method of the your Graphics area to determine if the Shape is fully contained within your panel.
Check out Playing With Shapes for more information and ideas.

use Ellipse2D.Float to instanciate an object for example:
Shape circle = new Ellipse2D.Float(100.0f, 100.0f, 100.0f, 100.0f);
basically the parameters,from left to right, are: Height, Width, X of the Top left and Y of the top left, and by keeping the X and Y both greater or equal to zero, your circle will always be visible.
the parameters of the Float(...) are documented for the Ellipse2D.Float in Java SE 7 in
http://docs.oracle.com/javase/7/docs/api/java/awt/geom/Ellipse2D.Float.html

Graphics2D - Rotating Shapes on a Graphics2D object

I have a Graphics2D object which I use to draw on my Canvas. I draw multiple shapes on the Canvas and want to transform only one (or part) of them.
I'll try to keep this simple:
void render(Graphics2D g) {
... // Draw shape 1
... // Draw shape 2
... // Draw shape 3
}
How would I go about rotating shape 2 while leaving shape 1 and 3 intact? By "rotate" I mean rotating around its center point, which we can define as x and y for example.
I've been looking for a way to do this for a while now, but couldn't find anything that works the way I want it to.
Is there any simple way to do this?

Rather than rotating the shape around it's centre point, rotate and then translate the canvas. To rotate around the centre of the shape at (x, y), first translate the canvas by (-x, -y) and then rotate the canvas -d degrees and draw the shape as normal at (0,0).
When you're done, rotate back then translate back (note that with these geometric transformations the order is important, translating and then rotating will give you a completely different outcome).
This means that you can still draw an object at any rotation without having to recalculate the coordinates yourself.

AffineTransform afx = new AffineTransform();
afx.rotate(angleRad, s.getCenter().x, s.getCenter().y);
//afx.rotate(angleRad);
java.awt.Shape ss = afx.createTransformedShape(s.getPrimativeShape());
return ss;
s is my wrapper class for java.awt.Shape and does some stuff with it.... But what you want is in line 2.
afx.rotate(Angle,xAnchorPoint,yAnchorPoint);
afx.rotate rotates the object about the point (xAnchorPoint;yAnchorPoint).
Hope this is what you wanted

In order to rotate a shape, use one of the Graphics2D.rotate methods.
Cache the transform used for both shape 1 and shape 3. Before drawing shape 3, ensure that you reset the transform to the cached one, since using rotate for shape 2 will alter the current transform coordinates.
Steps:
Cache current transform
Draw shape 1
Rotate
Draw shape 2
Set transform to cached one
Draw shape 3