We Keep Coding

Find Centroid of Quadrilateral

Help me please with how to find Centroid of Quadrilateral? I have this constructor:
public Quadrilateral(Point a, Point b, Point c, Point d) {
if (a == null || b == null || c == null || d == null) {
throw new IllegalArgumentException();
}
if (collinear(a, b, c)) {
throw new IllegalArgumentException();
}
double[][] points = { { a.getX(), a.getY() }, { b.getX(), b.getY() },
{ c.getX(), c.getY() }, { d.getX(), d.getY() } };
if (!isConvex(points)) {
throw new IllegalArgumentException();
}
this.a = a;
this.b = b;
this.c = c;
this.d = d;
}
Then I find four centroids of triangles inside quadrilateral:
public Point centroid() {
Point center1 = centroidTriangle(a,b,c);
Point center2 = centroidTriangle(a,c,d);
Point center3 = centroidTriangle(a,d,b);
Point center4 = centroidTriangle(b,d,c);
return null;
}
private Point centroidTriangle(Point a, Point b, Point c) {
double xx = (a.getX() + b.getX() + c.getX()) / 3;
double xy = (a.getY() + b.getY() + c.getY()) / 3;
return new Point(xx, xy);
}
Then I need to find two diagonals between "leftUp" - "rightDown" and "leftDown"-"rightUp" centroids.
But how can I find position of centroid to make correct pairs of them? And how to find then centroid of all quadrilateral?

Good day.
After finding centers of triangles you need to find intersection of lines which made with (center1,center2) and (center3,center4). So point of intersection is Centroid of Quadrilateral
public Point centroid() {
Point center1 = centroidTriangle(a,b,c);
Point center2 = centroidTriangle(a,c,d);
Point center3 = centroidTriangle(a,d,b);
Point center4 = centroidTriangle(b,d,c);
return new Segment(center1,center2)
.intersection(new Segment(center3,center4));
}
Segment:
import java.util.Objects;
import static java.lang.Math.sqrt;
import static java.lang.StrictMath.pow;
class Segment {
Point start;
Point end;
public Segment(Point start, Point end) {
if(Objects.isNull(start) || Objects.isNull(end) || start.equals(end))
throw new RuntimeException();
this.start = start;
this.end = end;
}
double length() {
return sqrt(pow(end.getX() - start.getX(), 2) + pow(end.getY() - start.getY(), 2));
}
Point middle() {
return new Point((start.getX() + end.getX()) / 2, (start.getY() + end.getY()) / 2);
}
Point intersection(Segment another) {
double k1 = (end.getY() - start.getY()) / (end.getX() - start.getX());
double k2 = (another.end.getY() - another.start.getY()) / (another.end.getX() - another.start.getX());
if (k1 == k2) return null;
double b1 = (start.getY() * end.getX() - end.getY() * start.getX()) / (end.getX() - start.getX());
double b2 = (another.start.getY() * another.end.getX() - another.end.getY() * another.start.getX()) /
(another.end.getX() - another.start.getX());
double x = (b2 - b1) / (k1 - k2);
double y = (k1 * b2 - k2 * b1) / (k1 - k2);
if ((x > start.getX() && x > end.getX()) || (x > another.start.getX() && x > another.end.getX()) ||
(x < start.getX() && x < end.getX()) || (x < another.start.getX() && x < another.end.getX()) ||
(y > start.getY() && y > end.getY()) || (y > another.start.getY() && y > another.end.getY()) ||
(y < start.getY() && y < end.getY()) || (y < another.start.getY() && y < another.end.getY()))
return null;
return new Point(x, y);
}
}

How to detect if two paths intersect in android?

I'm making a small sprouts app where the user can draw paths between dots or on the screen with paths. I create arraylists of the coordinates of the paths and then attempt to compare them four points at a time to see if they intersect with paths already drawn. Right now, it isn't detecting any collisions. Here some of my code so far:
//ArrayList of the currentPath that is being drawn
ArrayList<float[]> currentPath = new ArrayList<>();
//ArrayList of Paths that have been drawn so far
private ArrayList <ArrayList<float[]>> paths = new ArrayList<>();
public boolean checkPath() {
if (paths.size() == 0) {
return true;
} else {
boolean noCollisions = true;
for (int i = 0; i < paths.size(); i++) { //Loop through path array to compare each path
for (int j = 0; j < paths.get(i).size() - 1; j++) { //Loop through each path to compare points
for (int k = 0; k < currentPath.size() - 1; k++) {
float end1Y = currentPath.get(k + 1)[1];
float start1Y = currentPath.get(k)[1];
float start1X = currentPath.get(k)[0];
float end1X = currentPath.get(k + 1)[0];
float end2Y = paths.get(i).get(j + 1)[1];
float start2Y = paths.get(i).get(j)[1];
float start2X = paths.get(i).get(j)[0];
float end2X = paths.get(i).get(j + 1)[0];
double A1 = end1Y - start1Y;
double B1 = start1X - end1X;
double C1 = A1 * start1X + B1 + start1Y;
double A2 = end2Y - start2Y;
double B2 = start2X - end2X;
double C2 = A2 * start2X + B2 * start2Y;
double det = (A1 * B2) - (A2 * B1);
if (det == 0) {
//Lines are either parallel, are collinear or overlapping partially
if ((A1 * start2X) + (B1 * start2Y) == C1) {
//they are the on the same line, check if they are in the same space
if ((Math.min(start1X, end1X) < start2X) && (Math.max(start1X, end1X) > start2X)) {
noCollisions = false;
}
//one end point is okay, now checking the other
if ((Math.min(start1X, end1X) < end2X) && (Math.max(start1X, end1X) > end2X)) {
noCollisions = false;
} else{
noCollisions = true;
}
}
} else {
//Lines intersect somewhere, but do the segments intersect?
double x = (B2 * C1 - B1 * C2) / det;
double y = (A1 * C2 - A2 * C1) / det;
//check to see if the intersection is within the bounding box of the segments.
if((x > Math.min(start1X, end1X) && x < Math.max(start1X, end1X)) && (y > Math.min(start1Y, end1Y) && y < Math.max(start1Y, end1Y))){
//We are within the bounding box of the first line segment, now check the second
if((x > Math.min(start2X, end2X) && x < Math.max(start2X, end2X)) && (y > Math.min(start2Y, end2Y) && y < Math.max(start2Y, end2Y))){
//the segments intersect
noCollisions = false;
}
} else {
noCollisions = true;
}
}
}
}
}
return noCollisions;
}
}
I'm trying to use matrices and determinantes to figure out if there is any intersection occurring.

Please try to replace below line
double C1 = A1 * start1X + B1 + start1Y;
by following line
double C1 = A1 * start1X + B1 * start1Y;

Ain't this easier?
Region region1, region2;
boolean intersect;
Region clip = new Region(0, 0, screenWidth, screenHeight);
region1.setPath(path1, clip);
region2.setPath(path2, clip);
if (!region1.quickReject(region2))
intersect = true;
else intersect = false;
(I know I'm late)

jfeaturelib, java for glcm

I am doing my program using jfeaturelib for searching glcm features. I am using this haralick.java and already run my program perfectly using this demo HaralickDemo.java. All I want to know is how to use horizontal neigbhor 0 degree only or 90 degree only. This is the code:
private void calculate() {
calculateGreyValues();
final int imageWidth = image.getWidth();
final int imageHeight = image.getHeight();
final int d = HARALICK_DIST;
int i, j, pos;
// image is not empty per default
for (int y = 0; y < imageHeight; y++) {
for (int x = 0; x < imageWidth; x++) {
pos = imageWidth * y + x;
// horizontal neighbor: 0 degrees
i = x - d;
// j = y;
if (!(i < 0)) {
increment(grayValue[pos], grayValue[pos - d]);
}
// vertical neighbor: 90 degree
// i = x;
j = y - d;
if (!(j < 0)) {
increment(grayValue[pos], grayValue[pos - d * imageWidth]);
}
// 45 degree diagonal neigbor
i = x + d;
j = y - d;
if (i < imageWidth && !(j < 0)) {
increment(grayValue[pos], grayValue[pos + d - d * imageWidth]);
}
// 135 vertical neighbor
i = x - d;
j = y - d;
if (!(i < 0) && !(j < 0)) {
increment(grayValue[pos], grayValue[pos - d - d * imageWidth]);
}
}
}
And can you explain me detail of this haralick.java program?

Point in Polygon Android

I am developing an android application. In the application I have integrated map with polygon. Now I want to check whether the given marker is inside the polygon or not. Help Me please.
Following function is used to check the lat long in the polygon
pnpoly(no_of_vertex, lat, lng,(float) (point.latitude),(float) (point.longitude))
boolean pnpoly(int nvert, float vertx[], float verty[], float testx, float testy)
{
int i, j;
boolean c = false;
for (i = 0, j = nvert-1; i < nvert; j = i++) {
if ( ((verty[i]>testy) != (verty[j]>testy)) &&
(testx < (vertx[j]-vertx[i]) * (testy-verty[i]) / (verty[j]-verty[i]) + vertx[i]) )
c =true;
}
return c;
}
I got the solution to my question following is the code
**private boolean isPointInPolygon(LatLng tap, ArrayList<LatLng> vertices) {
int intersectCount = 0;
for(int j=0; j<vertices.size()-1; j++) {
if( LineIntersect(tap, vertices.get(j), vertices.get(j+1)) ) {
intersectCount++;
}
}
return (intersectCount%2) == 1; // odd = inside, even = outside;
}
private boolean LineIntersect(LatLng tap, LatLng vertA, LatLng vertB) {
double aY = vertA.latitude;
double bY = vertB.latitude;
double aX = vertA.longitude;
double bX = vertB.longitude;
double pY = tap.latitude;
double pX = tap.longitude;
if ( (aY>pY && bY>pY) || (aY<pY && bY<pY) || (aX<pX && bX<pX) ) {
return false; }
double m = (aY-bY) / (aX-bX);
double bee = (-aX) * m + aY; // y = mx + b
double x = (pY - bee) / m;
return x > pX;
}**

Processing/Line Graphing - Help

I posted something similar yesterday, but got nothing. I spent a few hours today problem-solving, but didn't progress any.
I'm using Processing (the language) and trying to implement a method that draws a line between two points. (I don't want to use the library's line() method.)
My lineCreate method works great for positive slopes, but fails with negative slopes. Can you help figure out why?
Here's the lineCreate() code:
void createLine(int x0, int y0, int x1, int y1){
//...
// Handle slanted lines...
double tempDX = x1 - x0;
double tempDY = y1 - y0; // Had to create dx and dy as doubles because typecasting dy/dx to a double data type wasn't working.
double m = (-tempDY / tempDX); // m = line slope. (Note - The dy value is negative
int deltaN = (2 * -dx); // deltaX is the amount to increment d after choosing the next pixel on the line.
int deltaNE = (2 * (-dy - dx)); // ...where X is the direction moved for that next pixel.
int deltaE = (2 * -dy); // deltaX variables are used below to plot line.
int deltaSE = (2 * (dy + dx));
int deltaS = (2 * dx);
int x = x0;
int y = y0;
int d = 0; // d = Amount d-value changes from pixel to pixel. Depends on slope.
int region = 0; // region = Variable to store slope region. Different regions require different formulas.
if(m > 1){ // if-statement: Initializes d, depending on the slope of the line.
d = -dy - (2 * dx); // If slope is 1-Infiniti. -> Use NE/N initialization for d.
region = 1;
}
else if(m == 1)
region = 2;
else if(m > 0 && m < 1){
d = (2 * -dy) - dx; // If slope is 0-1 -> Use NE/E initialization for d.
region = 3;
}
else if(m < 0 && m > -1){
d = (2 * dy) + dx; // If slope is 0-(-1) -> Use E/SE initliazation for d.
region = 4;
}
else if(m == -1)
region = 5;
else if(m < -1){
d = dy + (2 * dx); // If slope is (-1)-(-Infiniti) -> Use SE/S initialization for d.
region = 6;
}
while(x < x1){ // Until points are connected...
if(region == 1){ // If in region one...
if(d <= 0){ // and d<=0...
d += deltaNE; // Add deltaNE to d, and increment x and y.
x = x + 1;
y = y - 1;
}
else{
d += deltaN; // If d > 0 -> Add deltaN, and increment y.
y = y - 1;
}
}
else if(region == 2){
x = x + 1;
y = y - 1;
}
else if(region == 3){ // If region two...
if(d <= 0){
d += deltaE;
x = x + 1;
}
else{
d += deltaNE;
x = x + 1;
y = y - 1;
}
}
else if(region == 4){ // If region three...
if(d <= 0){
d += deltaSE;
x = x + 1;
y = y + 1;
}
else{
d += deltaE;
x = x + 1;
}
}
else if(region == 5){
x = x + 1;
y = y + 1;
}
else if(region == 6){ // If region four...
if(d <= 0){
d += deltaSE;
x = x + 1;
y = y + 1;
}
else{
d += deltaS;
y = y + 1;
}
}
point(x, y); // Paints new pixel on line going towards (x1,y1).
}
return;
}

Have a look at this page. It explains the whole theory behind line drawing with code examples.
There are a number of known algorithm for line drawing. Read about them here.