i'm working on a graphic interface for drawing subway maps. A line is represented with station as circles and a polyline to link them.You can move the stations with a mouseDrag and of course it updates the displaying map in real time. My problem is when stations comes to a certain angle, there is a polyline distortion and the corner created by the 2 lines is out of the station circle display, i'd like to know if there is a way to avoid this.
screenshots of the app with the polyline issue
here's my code for the polyline's draw
//x and y point array creation
xPoints = new int[this.stationViews.size()];
yPoints = new int[this.stationViews.size()];
for (int i=0;i<this.stationViews.size();i++) {
//fill arrays with the center point of circles representing stations
xPoints[i] = this.stationViews.get(i).getStation().getPosX()-this.stationViews.size()/2;
yPoints[i] = this.stationViews.get(i).getStation().getPosY()-this.stationViews.size();
}
//setting color
g2D.setColor(this.line.getColor());
//set stroke width relative to the zoom level
int strokeWidth=5;
if(!this.stationViews.isEmpty()) {
if (this.stationViews.get(0).getStationSize()>14) {
strokeWidth = this.stationViews.get(0).getStationSize()-13;
}else {
strokeWidth = 3;
}
}
g2D.setStroke(new BasicStroke(strokeWidth));
//draw the polyline
if (this.stationViews.size() >1) {
g2D.drawPolyline(xPoints, yPoints, this.stationViews.size());
}
//draw the station (g2D.drawCircle)
for (StationView stationView : stationViews) {
stationView.affiche(g2D,this.line.getColor());
}
thank you for your help
That is called the miter. You seem to be per default using JOIN_MITER, sharp joining of extended lines at the end, which can point far out of the join for small angles.
g2d.setStroke(new BasicStroke(strokeWidth,
BasicStroke.CAP_SQUARE, BasicStroke.JOIN_ROUND, 5));
miter a surface forming the beveled end or edge of a piece where a joint is made by cutting two pieces at an angle and fitting them together.
It is also a bishop's cap with a pointy top, hence the name.
I'm trying to detect a collision between a small rectangle around the cursor and a "Connector", which is basically just a line between two points.
Now, I've decided to use the Intersector.intersectLinePolygon(p1, p2, polygon) method to do so, but when I run the code. It detects a collision everytime any of the rectangle X or Y points are in the same range as the line's bounding box and I can't really get my head around it. The desired result is the collision reporting only when the rectangle is actually touching the line.
Vector3 worldPos = cam.unproject(new Vector3(mouseX, mouseY, 0));
Rectangle rect = new Rectangle(worldPos.x-4, worldPos.y-4, 8, 8);
Boolean connectorIntersected = false;
for (int i = 0; i < nodeConnectorHandler.getAllConnectors().size(); i++) {
//Getting two points that make the connector line
Node n1 = nodeConnectorHandler.getAllConnectors().get(i).getFrom();
Node n2 = nodeConnectorHandler.getAllConnectors().get(i).getTo();
float x1 = n1.getCX();
float y1 = n1.getCY();
float x2 = n2.getCX();
float y2 = n2.getCY();
//Making a polygon out of rect
Polygon p = new Polygon(new float[] {
rect.getX(),
rect.getY(),
(rect.getX()+8f),
rect.getY(),
(rect.getX()+8f),
(rect.getY()+8f),
rect.getX(),
(rect.getY()+8f)
});
//Checking if the line intersects the polygon (representing the rectangle around the cursor)
if (Intersector.intersectLinePolygon(new Vector2(x1,y1), new Vector2(x2,y2), p))
{
selectedIndex = nodeConnectorHandler.getAllConnectors().get(i).getID();
System.out.println("ConnectorIntersected!");
connectorIntersected = true;
}
break
}
The code reports a collision everytime the rectangle is in these areas (shown in yellow, aprox):
photoshopped image link
The red line inbetween those 2 dots is the "connector"
Cursor is right below the line. It reports a collision in those yellow areas spanning across the whole game world.
I suppose I'm either not using the function properly or that I've made some obvious mistake. Or is this how the function should react? I really don't know. Thanks for any help :)
Ok, apparently I used the wrong method. intersectSegmentPolygon works as expected. My bad ¯_(ツ)_/¯.
I'm currently looking into the drawPolygon(int[] xPoints, int[] yPoints, int nPoints) method in Java.
If I am not mistaken, the first two parameters are arrays, indicating the x-coordinates and y-coordinates of the polygon.
My question is, how are the polygon's coordinates interpreted from the two arrays?
For instance, I want to draw a line between the points (100, 300) and (200, 400). That is, a line increasing from left to right.
However, if I put these values into their respective arrays:
xPoints = {100, 200}; //x-coordinates
yPoints = {300, 400}; //y-coordinates
I get a line decreasing from left to right. As if the points are interpreted (100, 400) and (200, 300).
Thus, my question is: how are the array elements evaluated to make up the points of the polygon?
Thanks!
The default coordinate system has the origin in the upper left hand side corner of the canvas, and the y values increase from the top of the screen downwards. You can use an affine transform if you aren't happy with this orientation.
This is an example (!) from some code I have lying around - you may have to adapt it according to your situation:
// Polygon -> PathIterator -> Path2D, and then:
Path2D path = ...;
at.scale( 1, -1 );
path.transform( at );
bbox = path.getBounds2D();
at = new AffineTransform();
at.translate( -bbox.getMinX(), -bbox.getMinY() );
path.transform( at );
The coordinate system has origo in the top-left corner, and the y-axis increasing downwards.
This is why you get a downward slope when you increase the y-coordinate.
This is my situation. It involves aligning a scanned image which will account for incorrect scanning. I must align the scanned image with my Java program.
These are more details:
There is a table-like form printed on a sheet of paper, which will be scanned into an image file.
I will open the picture with Java, and I will have an OVERLAY of text boxes.
The text boxes are supposed to align correctly with the scanned image.
In order to align correctly, my Java program must analyze the scanned image and detect the coordinates of the edges of the table on the scanned image, and thus position the image and the textboxes so that the textboxes and the image both align properly (in case of incorrect scanning)
You see, the guy scanning the image might not necessarily place the image in a perfectly correct position, so I need my program to automatically align the scanned image as it loads it. This program will be reusable on many of such scanned images, so I need the program to be flexible in this way.
My question is one of the following:
How can I use Java to detect the y coordinate of the upper edge of the table and the x-coordinate of the leftmost edge of the table. The table is a a regular table with many cells, with black thin border, printed on a white sheet of paper (horizontal printout)
If an easier method exists to automatically align the scanned image in such a way that all scanned images will have the graphical table align to the same x, y coordinates, then share this method :).
If you don't know the answer to the above to questions, do tell me where I should start. I don't know much about graphics java programming and I have about 1 month to finish this program. Just assume that I have a tight schedule and I have to make the graphics part as simple as possible for me.
Cheers and thank you.
Try to start from a simple scenario and then improve the approach.
Detect corners.
Find the corners in the boundaries of the form.
Using the form corners coordinates, calculate the rotation angle.
Rotate/scale the image.
Map the position of each field in the form relative to form origin coordinates.
Match the textboxes.
The program presented at the end of this post does the steps 1 to 3. It was implemented using Marvin Framework. The image below shows the output image with the detected corners.
The program also outputs: Rotation angle:1.6365770416167182
Source code:
import java.awt.Color;
import java.awt.Point;
import marvin.image.MarvinImage;
import marvin.io.MarvinImageIO;
import marvin.plugin.MarvinImagePlugin;
import marvin.util.MarvinAttributes;
import marvin.util.MarvinPluginLoader;
public class FormCorners {
public FormCorners(){
// Load plug-in
MarvinImagePlugin moravec = MarvinPluginLoader.loadImagePlugin("org.marvinproject.image.corner.moravec");
MarvinAttributes attr = new MarvinAttributes();
// Load image
MarvinImage image = MarvinImageIO.loadImage("./res/printedForm.jpg");
// Process and save output image
moravec.setAttribute("threshold", 2000);
moravec.process(image, null, attr);
Point[] boundaries = boundaries(attr);
image = showCorners(image, boundaries, 12);
MarvinImageIO.saveImage(image, "./res/printedForm_output.jpg");
// Print rotation angle
double angle = (Math.atan2((boundaries[1].y*-1)-(boundaries[0].y*-1),boundaries[1].x-boundaries[0].x) * 180 / Math.PI);
angle = angle >= 0 ? angle : angle + 360;
System.out.println("Rotation angle:"+angle);
}
private Point[] boundaries(MarvinAttributes attr){
Point upLeft = new Point(-1,-1);
Point upRight = new Point(-1,-1);
Point bottomLeft = new Point(-1,-1);
Point bottomRight = new Point(-1,-1);
double ulDistance=9999,blDistance=9999,urDistance=9999,brDistance=9999;
double tempDistance=-1;
int[][] cornernessMap = (int[][]) attr.get("cornernessMap");
for(int x=0; x<cornernessMap.length; x++){
for(int y=0; y<cornernessMap[0].length; y++){
if(cornernessMap[x][y] > 0){
if((tempDistance = Point.distance(x, y, 0, 0)) < ulDistance){
upLeft.x = x; upLeft.y = y;
ulDistance = tempDistance;
}
if((tempDistance = Point.distance(x, y, cornernessMap.length, 0)) < urDistance){
upRight.x = x; upRight.y = y;
urDistance = tempDistance;
}
if((tempDistance = Point.distance(x, y, 0, cornernessMap[0].length)) < blDistance){
bottomLeft.x = x; bottomLeft.y = y;
blDistance = tempDistance;
}
if((tempDistance = Point.distance(x, y, cornernessMap.length, cornernessMap[0].length)) < brDistance){
bottomRight.x = x; bottomRight.y = y;
brDistance = tempDistance;
}
}
}
}
return new Point[]{upLeft, upRight, bottomRight, bottomLeft};
}
private MarvinImage showCorners(MarvinImage image, Point[] points, int rectSize){
MarvinImage ret = image.clone();
for(Point p:points){
ret.fillRect(p.x-(rectSize/2), p.y-(rectSize/2), rectSize, rectSize, Color.red);
}
return ret;
}
public static void main(String[] args) {
new FormCorners();
}
}
Edge detection is something that is typically done by enhancing the contrast between neighboring pixels, such that you get a easily detectable line, which is suitable for further processing.
To do this, a "kernel" transforms a pixel according it the pixel's inital value, and the value of that pixel's neighbors. A good edge detection kernel will enhance the differences between neighboring pixels, and reduce the strength of a pixel with similar neigbors.
I would start by looking at the Sobel operator. This might not return results that are immediately useful to you; however, it will get you far closer than you would be if you were to approach the problem with little knowledge of the field.
After you have some crisp clean edges, you can use larger kernels to detect points where it seems that a 90% bend in two lines occurs, that might give you the pixel coordinates of the outer rectangle, which might be enough for your purposes.
With those outer coordinates, it still is a bit of math to make the new pixels be composted with the average values between the old pixels rotated and moved to "match". The results (especially if you do not know about anti-aliasing math) can be pretty bad, adding blur to the image.
Sharpening filters might be a solution, but they come with their own issues, mainly they make the picture sharper by adding graininess. Too much, and it is obvious that the original image is not a high-quality scan.
I researched the libraries but in the end I found it more convenient to code up my own edge detection methods.
The class below will detect black/grayed out edges of a scanned sheet of paper that contains such edges, and will return the x and y coordinate of the edges of the sheet of paper, starting from the rightmost end (reverse = true) or from lower end (reverse = true) or from the top edge (reverse = false) or from left edge (reverse = false). Also...the program will take ranges along vertical edges (rangex) measured in pixels, and horizontal ranges (rangey) measured in pixels. The ranges determine outliers in the points received.
The program does 4 vertical cuts using the specified arrays, and 4 horizontal cuts. It retrieves the values of the dark dots. It uses the ranges to eliminate outliers. Sometimes, a little spot on the paper may cause an outlier point. The smaller the range, the fewer the outliers. However, sometimes the edge is slightly tilted, so you don't want to make the range too small.
Have fun. It works perfectly for me.
import java.awt.image.BufferedImage;
import java.awt.Color;
import java.util.ArrayList;
import java.lang.Math;
import java.awt.Point;
public class EdgeDetection {
public App ap;
public int[] horizontalCuts = {120, 220, 320, 420};
public int[] verticalCuts = {300, 350, 375, 400};
public void printEdgesTest(BufferedImage image, boolean reversex, boolean reversey, int rangex, int rangey){
int[] mx = horizontalCuts;
int[] my = verticalCuts;
//you are getting edge points here
//the "true" parameter indicates that it performs a cut starting at 0. (left edge)
int[] xEdges = getEdges(image, mx, reversex, true);
int edgex = getEdge(xEdges, rangex);
for(int x = 0; x < xEdges.length; x++){
System.out.println("EDGE = " + xEdges[x]);
}
System.out.println("THE EDGE = " + edgex);
//the "false" parameter indicates you are doing your cut starting at the end (image.getHeight)
//and ending at 0
//if the parameter was true, it would mean it would start the cuts at y = 0
int[] yEdges = getEdges(image, my, reversey, false);
int edgey = getEdge(yEdges, rangey);
for(int y = 0; y < yEdges.length; y++){
System.out.println("EDGE = " + yEdges[y]);
}
System.out.println("THE EDGE = " + edgey);
}
//This function takes an array of coordinates...detects outliers,
//and computes the average of non-outlier points.
public int getEdge(int[] edges, int range){
ArrayList<Integer> result = new ArrayList<Integer>();
boolean[] passes = new boolean[edges.length];
int[][] differences = new int[edges.length][edges.length-1];
//THIS CODE SEGMENT SAVES THE DIFFERENCES BETWEEN THE POINTS INTO AN ARRAY
for(int n = 0; n<edges.length; n++){
for(int m = 0; m<edges.length; m++){
if(m < n){
differences[n][m] = edges[n] - edges[m];
}else if(m > n){
differences[n][m-1] = edges[n] - edges[m];
}
}
}
//This array determines which points are outliers or nots (fall within range of other points)
for(int n = 0; n<edges.length; n++){
passes[n] = false;
for(int m = 0; m<edges.length-1; m++){
if(Math.abs(differences[n][m]) < range){
passes[n] = true;
System.out.println("EDGECHECK = TRUE" + n);
break;
}
}
}
//Create a new array only using valid points
for(int i = 0; i<edges.length; i++){
if(passes[i]){
result.add(edges[i]);
}
}
//Calculate the rounded mean... This will be the x/y coordinate of the edge
//Whether they are x or y values depends on the "reverse" variable used to calculate the edges array
int divisor = result.size();
int addend = 0;
double mean = 0;
for(Integer i : result){
addend += i;
}
mean = (double)addend/(double)divisor;
//returns the mean of the valid points: this is the x or y coordinate of your calculated edge.
if(mean - (int)mean >= .5){
System.out.println("MEAN " + mean);
return (int)mean+1;
}else{
System.out.println("MEAN " + mean);
return (int)mean;
}
}
//this function computes "dark" points, which include light gray, to detect edges.
//reverse - when true, starts counting from x = 0 or y = 0, and ends at image.getWidth or image.getHeight()
//verticalEdge - determines whether you want to detect a vertical edge, or a horizontal edge
//arr[] - determines the coordinates of the vertical or horizontal cuts you will do
//set the arr[] array according to the graphical layout of your scanned image
//image - this is the image you want to detect black/white edges of
public int[] getEdges(BufferedImage image, int[] arr, boolean reverse, boolean verticalEdge){
int red = 255;
int green = 255;
int blue = 255;
int[] result = new int[arr.length];
for(int n = 0; n<arr.length; n++){
for(int m = reverse ? (verticalEdge ? image.getWidth():image.getHeight())-1:0; reverse ? m>=0:m<(verticalEdge ? image.getWidth():image.getHeight());){
Color c = new Color(image.getRGB(verticalEdge ? m:arr[n], verticalEdge ? arr[n]:m));
red = c.getRed();
green = c.getGreen();
blue = c.getBlue();
//determine if the point is considered "dark" or not.
//modify the range if you want to only include really dark spots.
//occasionally, though, the edge might be blurred out, and light gray helps
if(red<239 && green<239 && blue<239){
result[n] = m;
break;
}
//count forwards or backwards depending on reverse variable
if(reverse){
m--;
}else{
m++;
}
}
}
return result;
}
}
A similar such problem I've done in the past basically figured out the orientation of the form, re-aligned it, re-scaled it, and I was all set. You can use the Hough transform to to detect the angular offset of the image (ie: how much it is rotated), but you still need to detect the boundaries of the form. It also had to accommodate for the boundaries of the piece of paper itself.
This was a lucky break for me, because it basically showed a black and white image in the middle of a big black border.
Apply an aggressive, 5x5 median filter to remove some noise.
Convert from grayscale to black and white (rescale intensity values from [0,255] to [0,1]).
Calculate the Principal Component Analysis (ie: calculate the Eigenvectors of the covariance matrix for your image from the calculated Eigenvalues) (http://en.wikipedia.org/wiki/Principal_component_analysis#Derivation_of_PCA_using_the_covariance_method)
4) This gives you a basis vector. You simply use that to re-orient your image to a standard basis matrix (ie: [1,0],[0,1]).
Your image is now aligned beautifully. I did this for normalizing the orientation of MRI scans of entire human brains.
You also know that you have a massive black border around the actual image. You simply keep deleting rows from the top and bottom, and both sides of the image until they are all gone. You can temporarily apply a 7x7 median or mode filter to a copy of the image so far at this point. It helps rule out too much border remaining in the final image from thumbprints, dirt, etc.
i have made a transform and rendered a Polygon object with it(mesh is of type Polygon):
at.setToTranslation(gameObject.position.x, gameObject.position.y);
at.rotate(Math.toRadians(rotation));
at.scale(scale, scale);
g2d.setTransform(at);
g2d.fillPolygon(mesh);
now i want to return the exact mesh i rendered so that i can do collision checks on it. only problem is that if i return mesh it returns the un-transformed mesh. so i tried setting the transform to the Polygon object (mesh) like so:
mesh = (Polygon)at.createTransformedShape(mesh);
but unfortunately at.createTransformedShape() returns a Shape that can only be casted to Path2D.Double. so if anyone knows how to convert Path2D.Double to Polygon or knows another way to set the transformations to the mesh please please help.
If AffineTransform#createTransformedShape doesn't provide the desired result for Polygons (as it seems to be the case), you can split the Polygon into Points, transform each Point and combine into a new Polygon. Try:
//Polygon mesh
//AffineTransform at
int[] x = mesh.xpoints;
int[] y = mesh.ypoints;
int[] rx = new int[x.length];
int[] ry = new int[y.length];
for(int i=0; i<mesh.npoints; i++){
Point2d p = new Point2d.Double(x[i], y[i]);
at.transform(p,p);
rx[i]=p.x;
ry[i]=p.y;
}
mesh = new Polygon(rx, ry, mesh.npoints)