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Java geotools how to create coverage grid

How to create grid coverage when each cell is 5M ?
I found this :
GridCoverage2D coverage = reader.read(null);
// direct access
DirectPosition position = new DirectPosition2D(crs, x, y);
double[] sample = (double[]) coverage.evaluate(position); // assume double
// resample with the same array
sample = coverage.evaluate(position, sample);
Source : https://docs.geotools.org/latest/userguide/library/coverage/grid.html
I didn't found a lot of tutorial about how to create grid coverage on geotools...

To create an empty coverage you need to use the GridCoverageFactory and one of the create methods. Since you are not constructing from an existing image you need to provide some memory for your raster to be stored in (this can also hold any initial values you want). For this your choices are a float[][] or a WritableRaster. Finally, you need a Envelope to say where the coverage is and what it's resolution is (otherwise it is just an array of numbers), I favour using a ReferencedEnvelope so that I know what the units are etc, so in the example below I have used EPSG:27700 which is the OSGB national grid so I know that it is in metres and I can define the origin somewhere in the South Downs. By specifying the lower left X and Y coordinates and the upper right X and Y as resolution times the width and height (plus the lower left corner) the maths all works out to make sure that the size of my pixels is resolution.
So keeping it simple for now you could do something like:
float[][] data;
int width = 100;
int height = 200;
data = new float[width][height];
int resolution = 5;
for(int i=0;i<width;i++){
for(int j=0;j<height;j++ ){
data[i][j] = 0.0f;
}
}
GridCoverageFactory gcf = new GridCoverageFactory();
CoordinateReferenceSystem crs = CRS.decode("EPSG:27700");
int llx = 500000;
int lly = 105000;
ReferencedEnvelope referencedEnvelope = new ReferencedEnvelope(llx, llx + (width * resolution), lly, lly + (height * resolution),
crs);
GridCoverage2D gc = gcf.create("name", data, referencedEnvelope);
If you want more bands in your coverage then you need to use a WriteableRaster as the base for your coverage.
WritableRaster raster2 = RasterFactory.createBandedRaster(java.awt.image.DataBuffer.TYPE_INT, width,
height, 3, null);
for (int i = 0; i < width; i++) {//width...
for (int j = 0; j < height; j++) {
raster2.setSample(i, j, 0, rn.nextInt(200));
raster2.setSample(i, j, 1, rn.nextInt(200));
raster2.setSample(i, j, 2, rn.nextInt(200));
}
}

Catmull Rom Spline implementation (LibGDX)

I want to generate a random spline across my screen.
Here is what I have so far:
public class CurvedPath {
Random rn;
CatmullRomSpline<Vector2> curve;
float[] xPts;
float[] yPts;
Vector2[] points;
public CurvedPath(){
points = new Vector2[10];
rn = new Random();
curve = new CatmullRomSpline<Vector2>(points,false);
for(int i = 0 ; i < 10; i++){
xPts[i] = rn.nextFloat()*SampleGame.WIDTH;
yPts[i] = SampleGame.HEIGHT*i/10;
}
}
}
I'm pretty confused on the documentation that has been provided on how to use the CatmullRomSpline object ( https://github.com/libgdx/libgdx/wiki/Path-interface-&-Splines )
Basically what I am trying to do here is generate 10 random points equally distributed across the height of my screen, and randomly placed along the width of the screen to create a randomized curved path.
So within the constructor's for loop you can see that I generate the x and y values of each control point for the spline.
How can I give input these points into the spline object and render it on the screen?
-thanks
update
Let me reword my question to be a little more specific..
I have my control points represented by xPts and yPts. Now I want to get the points that fall along the spline, how do I do this using these two vectors? The constructor for a CatmullRomSpline takes a Vector2, not two float[] 's

what you did. Fill with points:
curve = new CatmullRomSpline<Vector2>(points,false);
To get a point on the curve:
Vector2 point = new Vector2();
curve.valueAt(point, 0.5f);
valueAt() Parameter explanation:
1 (point) the point you are looking for is stored in the Vector2 object.
float between 0 and 1, 0 is the first point, 1 the last one. 0.5f is middle. This float represents the hole distance from first to last point.
Getting and render 100 points can look like this:
Vector2 point = new Vector2();
for (int i = 0; i <= 100; i++) {
curve.valueAt(point, i * 0.01f);
// draw using point.x and point.y
}
answer to you edited question:
for(int i = 0 ; i < 10; i++){
points[i].x = rn.nextFloat()*SampleGame.WIDTH;
points[i].y = SampleGame.HEIGHT*i/10;
}
curve = new CatmullRomSpline<Vector2>(points,false);

The process is also detailed here: https://github.com/libgdx/libgdx/wiki/Path-interface-&-Splines
/*members*/
int k = 100; //increase k for more fidelity to the spline
Vector2[] points = new Vector2[k];
/*init()*/
CatmullRomSpline<Vector2> myCatmull = new CatmullRomSpline<Vector2>(dataSet, true);
for(int i = 0; i < k; ++i)
{
points[i] = new Vector2();
myCatmull.valueAt(points[i], ((float)i)/((float)k-1));
}

Checking 2 arrays to see if they have the same values?

I would like to compare two arrays to see if they have the same values.
If I have a array called
public static float data[][]
which holds Y coordinates of a terrain, how can I check that array with another
public static int coords[][]
without iterating through all the coordinates?
Both arrays have over 1000 values in them. Iterating through them is not an option, since I must iterate through them over four times per second.
I am doing this to attempt to find if two objects are colliding. I have attempted using libraries for this, however I cannot find per-coordinate collision detection as specific as I need it.
Edit: Why I am unable to just iterate through this small amount of vertices is this.
The problem is, this is a MultiPlayer game,and I would have to iterate through all 1000 coordinates for every player. Meaning that just 10 players online is 10,000 100 online is 100,000. You can see how easily that would lag or at least take up a large percentage of the CPU.
Input of coordinates into the "Data" variable:
try {
// Load the heightmap-image from its resource file
BufferedImage heightmapImage = ImageIO.read(new File(
"res/images/heightmap.bmp"));
//width = heightmapImage.getWidth();
//height = heightmapImage.getHeight();
BufferedImage heightmapColour = ImageIO.read(new File(
"res/images/colours.bmp"));
// Initialise the data array, which holds the heights of the
// heightmap-vertices, with the correct dimensions
data = new float[heightmapImage.getWidth()][heightmapImage
.getHeight()];
// collide = new int[heightmapImage.getWidth()][50][heightmapImage.getHeight()];
red = new float[heightmapColour.getWidth()][heightmapColour
.getHeight()];
blue = new float[heightmapColour.getWidth()][heightmapColour
.getHeight()];
green = new float[heightmapColour.getWidth()][heightmapColour
.getHeight()];
// Lazily initialise the convenience class for extracting the
// separate red, green, blue, or alpha channels
// an int in the default RGB color model and default sRGB
// colourspace.
Color colour;
Color colours;
// Iterate over the pixels in the image on the x-axis
for (int z = 0; z < data.length; z++) {
// Iterate over the pixels in the image on the y-axis
for (int x = 0; x < data[z].length; x++) {
colour = new Color(heightmapImage.getRGB(z, x));
data[z][x] = setHeight;
}
}
}catch (Exception e){
e.printStackTrace();
System.exit(1);
}
And how coordinates are put into the "coords" variable (Oh wait, it was called "Ship", not coords. I forgot that):
try{
File f = new File("res/images/coords.txt");
String coords = readTextFile(f.getAbsolutePath());
for (int i = 0; i < coords.length();){
int i1 = i;
for (; i1 < coords.length(); i1++){
if (String.valueOf(coords.charAt(i1)).contains(",")){
break;
}
}
String x = coords.substring(i, i1).replace(",", "");
i = i1;
i1 = i + 1;
for (; i1 < coords.length(); i1++){
if (String.valueOf(coords.charAt(i1)).contains(",")){
break;
}
}
String y = coords.substring(i, i1).replace(",", "");;
i = i1;
i1 = i + 1;
for (; i1 < coords.length(); i1++){
if (String.valueOf(coords.charAt(i1)).contains(",")){
break;
}
}
String z = coords.substring(i, i1).replace(",", "");;
i = i1 + 1;
//buildx.append(String.valueOf(coords.charAt(i)));
////System.out.println(x);
////System.out.println(y);
////System.out.println(z);
//x = String.valueOf((int)Double.parseDouble(x));
//y = String.valueOf((int)Double.parseDouble(y));
//z = String.valueOf((int)Double.parseDouble(z));
double sx = Double.valueOf(x);
double sy = Double.valueOf(y);
double sz = Double.valueOf(z);
javax.vecmath.Vector3f cor = new javax.vecmath.Vector3f(Float.parseFloat(x), Float.parseFloat(y), Float.parseFloat(z));
//if (!arr.contains(cor)){
if (cor.y > 0)
arr.add(new javax.vecmath.Vector3f(cor));
if (!ship.contains(new Vector3f((int) sx, (int) sy, (int) sz)))
ship.add(new Vector3f((int) sx, (int) sy, (int) sz));
// arr.add(new javax.vecmath.Vector3f(Float.parseFloat(x), Float.parseFloat(y), Float.parseFloat(z)));
}
Thanks!

You can do like this but only applicable for same data type.
Arrays.deepEquals(data, coords);
For single dimension Array you can use this
Arrays.equals(array1, array1);

Arrays.deepEquals(a, b);
Try this but this will work only if the elements are in order.

No way around it, I'm afraid. Comparing data sets to see if they are identical demands looking at all elements, by definition. On a side note, comparing 1000 values is nothing even on relatively old hardware. You can do it thousands of time per second.

Check if an array of points is inside an array of rectangles?

I have a list of vertices and a list of regions (which are square/rectangle) shaped. Vertex has x and y coordinates, and a region has (x, y, height and width). How can I efficiently check which vertex lies in which region for every vertex/region?
EDIT:
This is the code I wrote to do this.
if (!g.getVertices().isEmpty()) {
for (int i = 0; i < g.getVertices().size(); i++) {
Vertex v = g.getVertices().get(i);
Point vertexPoint = new Point(v.getX(), v.getY());
for (int j = 0; j < g.getNumberOfRegions(); j++) {
int x = g.getRegions().get(j).getX();
int y = g.getRegions().get(j).getY();
int height = g.getRegions().get(j).getHeight();
int width = g.getRegions().get(j).getWidth();
Grid regionGrid = new Grid(j+1, x, y, height, width);
Rectangle regionRectangle = new Rectangle(x, y, height, width);
if (regionRectangle.contains(vertexPoint)) {
System.out.println("Vertex " + v + " lies inside region " + regionGrid.getRegionID());
}
}
}
}
EDIT 2: I used this to generate the regions, but I need a way to assign each region in the grid a regionID from left to right. For example:
1 - 2 - 3
4 - 5 - 6
7 - 8 - 9
for a 3x3 grid. At the moment it is in the following form:
1 - 1 - 1
2 - 2 - 2
3 - 3 - 3
for (int i = 0; i < rowValue; i++) {
for (int j = 0; j < columnValue; j++) {
Grid r = new Grid(0, 20 + i * size, 20 + j * size, size, size);
r.setRegionID(j + 1);
g.addRegion(r);
}
}

checking if a vertex is inside a square or a circle can be done in O(1). you can do it with library function or elementary math. so the works algorithm you can create is O(#vertices * #regions). you can try to optimise by sorting the vertices and regions by X-axis and then by Y-axis and try to eliminate checking that for sure return false. but seems that in pessimistic scenario you will still have O(#vertices * #regions) time.

You can probably use the Core Java libraries itself:
List<Rectangle2D.Double> rectangles = Arrays.asList(
new Rectangle2D.Double(0d, 0d, 100d, 100d),
new Rectangle2D.Double(100d, 0d, 100d, 100d),
new Rectangle2D.Double(0d, 100d, 100d, 100d),
new Rectangle2D.Double(100d, 100d, 100d, 100d));
Point2D.Double aPoint = new Point2D.Double(30d, 40d);
for (Rectangle2D.Double rectangle:rectangles){
if (rectangle.contains(aPoint)){
System.out.println(rectangle + " has the point " + aPoint);
}
}

Working with plane geometry is extremely easy while using JTS. You can try convert the objects you are using to JTS-specific.

How to avoid overlapping polygon

I created a program to draw many polygons automatically everytimes user presses a button. The points of the polygon are generated automatically using the random function. The problem is that, since the points of the polygon were randomly generated, some of the polygon are overlap with other polygon. How can I avoid this, so that every polygon shown without being overlapped?
.....
List<Polygon> triangles = new LinkedList<Polygon>();
Random generator = new Random();
public void paintComponent(Graphics g) {
for(int i = 0; i < 10; i++) {
double xWidth = generator.nextDouble() * 40.0 + 10.0;
double yHeight = generator.nextDouble() * 40.0 + 10.0;
xCoord[0] = generator.nextInt(MAX_WIDTH);
yCoord[0] = generator.nextInt(MAX_HEIGHT);
xCoord[1] = (int) (xCoord[0] - xWidth);
xCoord[2] = (int) (xCoord[1] + (xWidth/2));
yCoord[1] = yCoord[0];
yCoord[2] = (int) (yCoord[1] - yHeight);
triangles.add( new Polygon(xCoord,yCoord, 3));
}
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2.setStroke(new BasicStroke(1));
g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 1.00f));
g2.setPaint(Color.black);//set the polygon line
for (Polygon triangle : triangles) g2.drawPolygon(triangle);
Polygon[] triArray = triangles.toArray(new Polygon[triangles.size()]);
for (Polygon p:triArray) triangles.remove (p);
}

Check out the game programming wiki on Polygon Collision:
http://gpwiki.org/index.php/Polygon_Collision

You could break your canvas into 10 regions and constrain your polygons each to their own region. To do this, you could use your i value and a %100 (or other suitable magnitude) of your randomly generated value and apply them to your x coordinates and y coordinates as applicable. The result would be a grid of similarly constrained(no larger than the grid cell), but randomly shaped, Polygons.
EDIT:
Taking another look and fooling around a bit, I took the general concept as I described above and made a stab at an implementation:
public void paintComponent(Graphics g) {
int[] xCoord = new int[3];
int[] yCoord = new int[3];
int colCnt = 5;
int rowCnt = 2;
int maxCellWidth = getWidth() / colCnt;
int maxCellHeight = getHeight() / rowCnt;
for (int i = 0; i < (colCnt * rowCnt); i++) {
int xMultiple = i % colCnt;
int yMultiple = i / colCnt;
for (int j = 0; j < 3; j++) {
xCoord[j] = generator.nextInt(maxCellWidth)
+ (maxCellWidth * xMultiple);
yCoord[j] = generator.nextInt(maxCellHeight)
+ (maxCellHeight * yMultiple);
}
triangles.add(new Polygon(xCoord, yCoord, 3));
}
//... the rest of your method
}
As you can see, all of the Polygons have all points randomly generated, as opposed to your method of generating the first point and then making the rest relative to the first. There is a sense of randomness that is lost, however, as the Polygons are laid out in a grid-like pattern.

Create Area objects from your new polygon as well as for all existing polygons.
Subtract the new polygon's area from the existing ones. If the subtract changed the area, the polygons overlap.
Area newArea = new Area(newPolygon);
Area existingArea = new Area(existingPolygon);
Area existingAreaSub = new Area(existingPolygon); existingAreaSub.subtract(newArea);
boolean intersects = existingAreaSub.equals(existingArea);

You could implement a method Polycon.containsPoint( x, y ) and repeat your random generation until this method returns false for all drawn Polygons.

I have achieved this in Android Using Kotlin (See github project) by using JTS see here
Step-1:
Add JTS library to your project
implementation group: 'org.locationtech.jts', name: 'jts-core', version: '1.15.0'
Step-2:
Create JTS polygon objects for both polygon
// create polygons One
var polygoneOneArray: ArrayList<Coordinate> = ArrayList()
for (points in polygonOnePointsList) {
polygoneOneArray.add(Coordinate(points.latitude(), points.longitude()))
}
val polygonOne: org.locationtech.jts.geom.Polygon = GeometryFactory().createPolygon(
polygoneOneArray.toTypedArray()
)
// create polygons Two
var polygoneTwoArray: ArrayList<Coordinate> = ArrayList()
for (points in polygoneTwoPointsList) {
polygoneTwoArray.add(Coordinate(points.latitude(), points.longitude()))
}
val polygonTwo: org.locationtech.jts.geom.Polygon = GeometryFactory().createPolygon(
polygoneTwo.toTypedArray()
)
Step-3:
Get Common Area of both Polygon
val intersection: org.locationtech.jts.geom.Geometry = polygonOne.intersection(polygonTwo)
Step-4:
Remove common Area from polygonTwo
val difference: org.locationtech.jts.geom.Geometry = polygonTwo.difference(intersection)
Step-5:
Merge Both polygonOne and update polygonTwo
val union: org.locationtech.jts.geom.Geometry = mergePolygonList.get(0).polygons.union(difference)
Step-5:
Now pick points from Geometry and draw a final merged Polygon
val array: ArrayList<Coordinate> = union.coordinates.toList() as ArrayList<Coordinate>
val pointList: ArrayList<Point> = ArrayList()
for (item in array) {
pointList.add(Point.fromLngLat(item.y, item.x))
}
var list: ArrayList<List<Point>> = ArrayList<List<Point>>()
list.add(pointList)
style.addSource(
GeoJsonSource(
"source-id${timeStamp}",
Feature.fromGeometry(Polygon.fromLngLats(list))
)
)