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Translate Java 3D coordinates to 2D screen coordinates

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2 replies [Last post]
Joined: 2010-09-25

Hi All,
I'm working with a Java 3D application called "Walrus" that is used to display directed graphs. The code already has a feature to highlight a node and draw label adjacent in graph given its screen coordinates.

Upon rotating the screen, the node is no more highlighted.

What I have is the node coordinates in 3D. I need to draw label to it.

Code for highlight using 3D coordinates
Point3d p = new Point3d();
m_graph.getNodeCoordinates(node, p);

PointArray array = new PointArray(1, PointArray.COORDINATES);
array.setCoordinate(0, p);


1. How can I draw Label with 3D coordinates( Raster graphics throws error Renderer: Error creating immediate mode Canvas3D graphics context )

2. How can I convert 3D coordinates to 2D screen and use existing code to draw label at 2D screen point


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Joined: 2004-03-25

Answer for question 2 :
plotting on the 2D screen a label at a position where the 3D nodes is projected on the screen:
the main issue I have at the moment is the calculte the X,Y position on the screen.
Here is a fonction I found on an old post :

    public Point2d get3DTo2DPoint(Point3d point3d)
>          {
>             Transform3D temp = new Transform3D();
>             this.canvas3D.getVworldToImagePlate(temp);
>             temp.transform(point3d);
>             Point2d point2d =new Point2d();
>             this.canvas3D.getPixelLocationFromImagePlate(point3d,point2d);
>             return point2d;
>          }

Please tell us if this code works.
a) temp::Transform3D just 'transform' a pure 3D-java3Dworld coordinates into a 3D-Image-Plamate coordinates.
b) I think the 'Image plate' coodinates is a XYZ coordinates but
- the origin : is located on the lower -left corner on the screen-of-camera (view Frustrum)
- the X axe is from left to right, the Y axe going up, the Z going away from the Screen.

Hope this helps

Joined: 2010-09-25

Hi All,
I found the solution.
This is the function to display Text3D at image 2D coordinates
public void drawLabel(GraphicsContext3D gc, double x, double y, int zOffset, String s) {
boolean frontBufferRenderingState = gc.getFrontBufferRendering();
Point3d eye = getEye();
double labelZ = zOffset * LABEL_Z_OFFSET_SCALE

double xOffset = LABEL_X_OFFSET * m_pixelToMeterScale;
double yOffset = LABEL_Y_OFFSET * m_pixelToMeterScale;
Point3d p = new Point3d(x + xOffset, y + yOffset, 0.0);
// Project given (x, y) coordinates to the plane z=labelZ.

// Convert from image-plate to eye coordinates.
p.x -= eye.x;
p.y -= eye.y;

double inversePerspectiveScale = 1.0 - labelZ / eye.z;
p.x *= inversePerspectiveScale;
p.y *= inversePerspectiveScale;

// Convert from eye to image-plate coordinates.
p.x += eye.x;
p.y += eye.y;


Transform3D scale = new Transform3D();

Vector3d t = new Vector3d(p.x, p.y, labelZ);
Transform3D translation = new Transform3D();

Transform3D transform = new Transform3D(m_imageToVworld);


int fontSize=(int)(10*m_magnification);


// XXX: Courier may not be available on all systems.
Text2D text = new Text2D(s, new Color3f(1.0f, 1.0f, 1.0f),
"Courier", fontSize, Font.BOLD);



// NOTE: Resetting the model transform here is very important.
// For some reason, not doing this causes the immediate
// following frame to render incorrectly (but subsequent
// frames will render correctly). In some ways, this
// makes sense, because most rendering code assumes that
// GraphicsContext3D has been set to some reasonable
// transform.

This is the function to take 3D coordinates and convert them to image 2D coordinates and render using above function
private boolean displayOnScreenLabel(int node, String label) {
boolean success = false;
try {
Transform3D transform = m_parameters.getObjectToEyeTransform();
Point3d nodeC = new Point3d();

m_graph.getNodeCoordinates(node, nodeC);

Point3d eye = m_parameters.getEye();

double perspectiveScale = 1.0 / (1.0 - nodeC.z / eye.z);

double centerX = eye.x + nodeC.x * perspectiveScale;
double centerY = eye.y + nodeC.y * perspectiveScale;

GraphicsContext3D gc = m_canvas.getGraphicsContext3D();

m_parameters.drawLabel(gc, centerX, centerY, m_labelZOffsetCounter++, label);

success = true;
} catch (final java.lang.OutOfMemoryError error) {
JOptionPane.showMessageDialog(m_frame, "The 3D Graphics is unable to find enough memory on your system. Kill the application!", "Out Of Memory!", JOptionPane.ERROR_MESSAGE);
} catch (Exception e) {
success = false;
return success;