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• Detect rotated rectangle collision

  - by handyface

  I'm trying to implement a script that detects whether two rotated rectangles collide for my game. I used the method explained in the following article for my implementation in Google Dart. 2D Rotated Rectangle Collision I tried to implement this code into my game. Basically from what I understood was that I have two rectangles, these two rectangles can produce four axis (two per rectangle) by subtracting adjacent corner coordinates. Then all the corners from both rectangles need to be projected onto each axis, then multiplying the coordinates of the projection by the axis coordinates (point.x*axis.x+point.y*axis.y) to make a scalar value and checking whether the range of both the rectangle's projections overlap. When all the axis have overlapping projections, there's a collision. First of all, I'm wondering whether my comprehension about this algorithm is correct. If so I'd like to get some pointers in where my implementation (written in Dart, which is very readable for people comfortable with C-syntax) goes wrong. Thanks!

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• Game Database Connectivity Java

  - by The Kraken

  I'm developing a simple multi-player puzzle game in Java. Both players should be able to view the same game board on his own computer. Then, when one player makes an action in the game (ex. drags an object onto a coordinate space), the game's view should update automatically on the other computer's game screen. I'd like all this to happen over the internet, not requiring both computers to be on the same LAN connection. If I need to use SQL/PHP to accomplish this, I'm unsure how to design the database to accomplish something as simple as the following: Player A drags element onscreen Game sends coordinates of element to database/server Player B's computer detects a change to an item in the database Player B's computer grabs the coordinates of Player A's item Player B's machine draws onscreen elements at the received coordinates Could somebody point me in the right direction?

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• How to reproject a shapefile from WGS 84 to Spherical/Web Mercator projection.

  - by samkea

  Definitions: You will need to know the meaning of these terms below. I have given a small description to the acronyms but you can google and know more about them. #1:WGS-84- World Geodetic Systems (1984)- is a standard reference coordinate system used for Cartography, Geodesy and Navigation. #2: EPGS-European Petroleum Survey Group-was a scientific organization with ties to the European petroleum industry consisting of specialists working in applied geodesy, surveying, and cartography related to oil exploration. EPSG::4326 is a common coordinate reference system that refers to WGS84 as (latitude, longitude) pair coordinates in degrees with Greenwich as the central meridian. Any degree representation (e.g., decimal or DMSH: degrees minutes seconds hemisphere) may be used. Which degree representation is used must be declared for the user by the supplier of data. So, the Spherical/Web Mercator projection is referred to as EPGS::3785 which is renamed to EPSG:900913 by google for use in googlemaps. The associated CRS(Coordinate Reference System) for this is the "Popular Visualisation CRS / Mercator ". This is the kind of projection that is used by GoogleMaps, BingMaps,OSM,Virtual Earth, Deep Earth excetra...to show interactive maps over the web with thier nearly precise coordinates.  Reprojection: After reading alot about reprojecting my coordinates from the deepearth project on Codeplex, i still could not do it. After some help from a colleague, i got my ball rolling.This is how i did it. #1 You need to download and open your shapefile using Q-GIS; its the one with the biggest number of coordinate reference systems/ projections. #2 Use the plugins menu, and enable ftools and the WFS plugin. #3 Use the Vector menu--> Data Management Tools and choose define current projection. Enable, use predefined reference system and choose WGS 84 coodinate system. I am personally in zone 36, so i chose WGS84-UTM Zone 36N under ( Projected Coordinate Systems--> Universal Transverse Mercator) and click ok. #4 Now use the Vector menu--> Data Management Tools and choose export to new projection. The same dialog will pop-up. Now choose WGS 84 EPGS::4326 under Geodetic Coordinate Systems. My Input user Defined Spatial Reference System should looks like this: +proj=tmerc +lat_0=0 +lon_0=33 +k=0.9996 +x_0=500000 +y_0=200000 +ellps=WGS84 +datum=WGS84 +units=m +no_defs Your Output user Defined Spatial Reference System should look like this: +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs Browse for the place where the shapefile is going to be and give the shapefile a name(like origna_reprojected). If it prompts you to add the projected layer to the TOC, accept. There, you have your re-projected map with latitude and longitude pair of coordinates. #5 Now, this is not the actual Spherical/Web Mercator projection, but dont worry, this is where you have to stop. All the other custom web-mapping portals will pick this projection and transform it into EPGS::3785 or EPSG:900913 but the coordinates will still remain as the LatLon pair of the projected shapefile. If you want to test, a particular know point, Q-GIS has a lot of room for that. Go ahead and test it.

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• Rendering Linear Gradients using the HTML5 Canvas

  - by dwahlin

  Related HTML5 Canvas Posts: Getting Started with the HTML5 Canvas Rendering Text with the HTML5 Canvas Creating a Line Chart using the HTML5 Canvas New Pluralsight Course: HTML5 Canvas Fundamentals Gradients are everywhere. They’re used to enhance toolbars or buttons and help add additional flare to a web page when used appropriately. In the past we’ve always had to rely on images to render gradients which works well, but isn’t necessarily the most efficient (although 1 pixel wide images do work well). CSS3 provides a great way to render gradients in modern browsers (see http://www.colorzilla.com/gradient-editor for a nice online gradient generator tool) but it’s not the only option. If you’re working with charts, games, multimedia or other HTML5 Canvas applications you can also use gradients and render them on the client-side without relying on images. In this post I’ll introduce how to use linear gradients and discuss the different functions that can be used to create them.   Creating Linear Gradients Linear gradients can be created using the 2D context’s createLinearGradient function. The function takes the starting x,y coordinates and ending x,y coordinates of the gradient:   createLinearGradient(x1, y1, x2, y2);   By changing the start and end coordinates you can control the direction that the gradient renders. For example, adding the following coordinates causes the gradient to render from left to right since the y value stays at 0 for both points while the x value changes from 0 to 200. var lgrad = ctx.createLinearGradient(0, 0, 200, 0); Here’s an example of how changing the coordinates affects the gradient direction:   Once a linear gradient object has been created you can set color stops using the addColorStop() function. It takes the location where the color should appear in the gradient with 0 being the beginning and 1 being at the end (0.5 would be in the middle) as well as the color to display in the gradient. lgrad.addColorStop(0, 'white'); lgrad.addColorStop(1, 'gray');   An example of combining createLinearGradient() with addColorStop() is shown next:   Using createLinearGradient() var canvas = document.getElementById('myCanvas'); var ctx = canvas.getContext('2d'); var lgrad = ctx.createLinearGradient(0, 0, 200, 0); lgrad.addColorStop(0, 'white'); lgrad.addColorStop(1, 'gray'); ctx.fillStyle = lgrad; ctx.fillRect(0, 0, 200, 200); ctx.strokeRect(0, 0, 200, 200); This code renders a white to gray gradient as shown next: A live example of using createLinearGradient() is shown next. Click the Result tab to see the code in action.   In the next post on the HTML5 Canvas I’ll take a look at radial gradients and how they can be used. In the meantime, if you’re interested in learning more about the HTML5 Canvas and how it can be used in your Web or Windows 8 applications, check out my HTML5 Canvas Fundamentals course from Pluralsight. It has over 4 1/2 hours of canvas goodness packed in it.

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• Graph layouting with Perl

  - by jonny

  Ok, I have a flowchart definition (basically, array of nodes and edges for each node). Now I want to calculate coordinates for every task in the flow, preferably hierarchycal style. I need something like Graph::Easy::Layout but I have no idea how to get nodes coordinates: I render nodes myself and I only want to retrieve box coordinates/size. Any suggestions? What I need is a cpan module avialable even in Debian repository.

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• Does Google's Geocoding API return results that are more accurate than Google Maps or the same?

  - by jacob501

  I am thinking about using python or C++ in conjunction with google's geocoding API. Since geocoding is the process of turning street addresses into coordinates, I was wondering how google does this. I am looking for something that will give me coordinates that are around 50 meters away from the entrance of the location at a specified address. There are a few problems with this when you use google maps however. If you aren't doing it manually, sometimes google maps will place a marker for an address just on the road and not over the place (especially for addresses in malls, places far off the road, etc). Does the geocoding api give you more accurate coordinates or does it simply copy the coordinates of what a google maps marker would give you? I hope this makes sense. Thanks.

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• OpenLayers Projections.

  - by Jenny

  I can succesfully do: point.transform(new OpenLayers.Projection("EPSG:900913"), new OpenLayers.Projection("EPSG:4326")); To a point that is in the google format (in meters), but when I want to do the reverse: point.transform(new OpenLayers.Projection("EPSG:4326"), new OpenLayers.Projection("EPSG:900913")); to a point that is in 4326 (regular lat/lon format), I am having some issues. Any negative value seems to become NaN (not a number) when I do the transformation. Is there something about the transformation in reverse that I don't understand? Edit: Even worse, when I have no negative values, the coordinates seem off. I am getting the coordinates by drawing a square on the screen, then saving those coordinates to a database and loading them later. I can draw a square near the tip of africa (positive coordinates), and then when it loads it's near the top of africa, in the atlantic ocean. I'm definitely doing something wrong....

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• change background color with change in mouse position

  - by Ashish Rajan

  I was wondering if it is possible to set background-color with help of mouse coordinates. What is have is: I have a DIV-A which is draggable and some other divs which are droppable. What is need is : I need to highlight other divs on my page which are droppable, whenever my DIV-A passes over them. What i have is mouse coordinates, is it possible to apply css on the bases of mouse coordinates using jquery.

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• Gruff: Draw a line

  - by Gjorgji

  I have two arrays: x = x coordinates and y = y coordinates. I want to use gruff to create a line based on the x and y coordinates. How can I do that?

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• How to recognize the touch of a non regular sprite image ?

  - by srikanth rongali

  I have a sprite and if it is touched the touch should be recognized. I used the coordinates to do so. I took the coordinates (min x, min y, max x , max y)of the sprite image. But The sprite image is not a rectangular shape. So, even if I touch the coordinates outside the sprite and inside the rectangular bounds the sprite is recognized. But for my application I need only the sprite to be recognized. So, I have to take only the coordinates of the sprite, but it is not regular shape. I am using CCSprite in my program. So, what can I do to for only the sprite to be selected ? Which classes should use for this? Thank You.

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• How can I transform latitude and longitude to x,y in Java?

  - by hory.incpp

  Hello, I am working on a geographic project in Java. The input are coordinates : 24.4444 N etc Output: a PLAIN map (not round) showing the point of the coordinates. I don't know the algorithm to transform from coordinates to x,y on a JComponent, can somebody help me? The map looks like this: http://upload.wikimedia.org/wikipedia/commons/7/74/Mercator-projection.jpg Thank you

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• pass array by reference in c

  - by Yassir

  How can I pass an array of struct by reference ? example : struct Coordinate { int X; int Y; }; SomeMethod(Coordinate *Coordinates[]){ //Do Something with the array } int main(){ Coordinate Coordinates[10]; SomeMethod(&Coordinates); }

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• BFS algorithm problem

  - by Gorkamorka

  The problem is as follows: A wanderer begins on the grid coordinates (x,y) and wants to reach the coordinates (0,0). From every gridpoint, the wanderer can go 8 steps north OR 3 steps south OR 5 steps east OR 6 steps west (8N/3S/5E/6W). How can I find the shortest route from (X,Y) to (0,0) using breadth-first search? Clarifications: Unlimited grid Negative coordinates are allowed A queue (linked list or array) must be used No obstacles present

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• Drawing and filling different polygons at the same time in MATLAB

  - by Hossein

  Hi,I have the code below. It load a CSV file into memory. This file contains the coordinates for different polygons.Each row of this file has X,Y coordinates and a string which tells that to which polygon this datapoint belongs. for example a polygone named "Poly1" with 100 data points has 100 rows in this file like : Poly1,X1,Y1 Poly1,X2,Y2 ... Poly1,X100,Y100 Poly2,X1,Y1 ..... The index.csv file has the number of datapoint(number of rows) for each polygon in file Polygons.csv. These details are not important. The thing is: I can successfully extract the datapoints for each polygon using the code below. However, When I plot the lines of different polygons are connected to each other and the plot looks crappy. I need the polygons to be separated(they are connected and overlapping the some areas though). I thought by using "fill" I can actually see them better. But "fill" just filles every polygon that it can find and that is not desirable. I only want to fill inside the polygons. Can someone help me? I can also send you my datapoint if necessary, they are less than 200Kb. Thanks [coordinates,routeNames,polygonData] = xlsread('Polygons.csv'); index = dlmread('Index.csv'); firstPointer = 0 lastPointer = index(1) for Counter=2:size(index) firstPointer = firstPointer + index(Counter) + 1 hold on plot(coordinates(firstPointer:lastPointer,2),coordinates(firstPointer:lastPointer,1),'r-') lastPointer = lastPointer + index(Counter) end

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• MATLAB: How do I get 3D coordiantes from a user-click?

  - by John

  I'm using Matlab to create a small chess game for one of my courses this semester. The thing I'm having trouble with is having the user be able to select one of the chess pieces. To simplify things, I'm making it so that the user selects a piece by clicking on the square that the chess piece resides on rather than clicking the piece itself (which I assume would be much more difficult). I know how to get the x and y coordinates of the view-port, but how do I transform these coordinates into 3-space coordinates? I know that there are multiple x,y,z coordinates associated with each view-port coordinate, but I'm only interested in the x,y,z coordinate where z = 0 (since the board itself is in the x,y plane that intersects the z axis where z = 0). Thanks!

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• iPhone SDK: Track users location using GPS

  - by Nic Hubbard

  I have a few questions about CoreLocation and GPS. First, what method in core location is used to continually get the users current coordinates? And at what interval should these be retrieved? Second, should these coordinates be pushed into a NSMutableArray each time they are received, so that the array of coordinates will represent the users path? Thanks, just wanting to get started getting me mind around this.

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• Undefined javascript function?

  - by user74283

  Working on a google maps project and stuck on what seems to be a minor issue. When i call displayMarkers function firebug returns: ReferenceError: displayMarkers is not defined [Break On This Error] displayMarkers(1); <script type="text/javascript"> function initialize() { var center = new google.maps.LatLng(25.7889689, -80.2264393); var map = new google.maps.Map(document.getElementById('map'), { zoom: 10, center: center, mapTypeId: google.maps.MapTypeId.ROADMAP }); //var data = [[25.924292, -80.124314], [26.140795, -80.3204049], [25.7662857, -80.194692]] var data = {"crs": {"type": "link", "properties": {"href": "http://spatialreference.org/ref/epsg/4326/", "type": "proj4"}}, "type": "FeatureCollection", "features": [{"geometry": {"type": "Point", "coordinates": [25.924292, -80.124314]}, "type": "Feature", "properties": {"industry": [2], "description": "hosp", "title": "shaytac hosp2"}, "id": 35}, {"geometry": {"type": "Point", "coordinates": [26.140795, -80.3204049]}, "type": "Feature", "properties": {"industry": [1, 2], "description": "retail", "title": "shaytac retail"}, "id": 48}, {"geometry": {"type": "Point", "coordinates": [25.7662857, -80.194692]}, "type": "Feature", "properties": {"industry": [2], "description": "hosp2", "title": "shaytac hosp3"}, "id": 36}]} var markers = []; for (var i = 0; i < data.features.length; i++) { var latLng = new google.maps.LatLng(data.features[i].geometry.coordinates[0], data.features[i].geometry.coordinates[1]); var marker = new google.maps.Marker({ position: latLng, title: console.log(data.features[i].properties.industry[0]), map: map }); marker.category = data.features[i].properties.industry[0]; marker.setVisible(true); markers.push(marker); } function displayMarkers(category) { var i; for (i = 0; i < markers.length; i++) { if (markers[i].category === category) { markers[i].setVisible(true); } else { markers[i].setVisible(false); } } } } google.maps.event.addDomListener(window, 'load', initialize); </script> <div id="map-container"> <div id="map"></div> </div> <input type="button" value="Retail" onclick="displayMarkers(1);">

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• determine if line segment is inside polygon

  - by dato

  suppose we have simple polygon(without holes) with vertices (v0,v1,....vn) my aim is to determine if for given point p(x,y) any line segment connecting this point and any vertices of polygon is inside polygon or even for given two point p(x0,y0) `p(x1,y1)` line segment connecting these two point is inside polygon? i have searched many sites about this ,but i am still confused,generally i think we have to compare coordinates of vertices and by determing coordinates of which point is less or greater to another point's coordinates,we could determine location of any line segment,but i am not sure how correct is this,please help me

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• MATLAB: How do I get 3D coordiantes from a user-click?

  - by Tim

  I'm using Matlab to create a small chess game for one of my courses this semester. The thing I'm having trouble with is having the user be able to select one of the chess pieces. To simplify things, I'm making it so that the user selects a piece by clicking on the square that the chess piece resides on rather than clicking the piece itself (which I assume would be much more difficult). I know how to get the x and y coordinates of the view-port, but how do I transform these coordinates into 3-space coordinates? I know that there are multiple x,y,z coordinates associated with each view-port coordinate, but I'm only interested in the x,y,z coordinate where z = 0 (since the board itself is in the x,y plane that intersects the z axis where z = 0). Thanks!

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• How do I select every 6th element from a list (using Linq)

  - by iDog

  Hi, I've got a list of 'double' values. I need to select every 6th record. It's a list of coordinates, where I need to get the minimum and maximum value of every 6th value. List of coordinates (sample): [2.1, 4.3, 1.0, 7.1, 10.6, 39.23, 0.5, ... ] with hundrets of coordinates. Result should look like: [x_min, y_min, z_min, x_max, y_max, z_max] with exactly 6 coordinates. Following code works, but it takes to long to iterate over all coordinates. I'd like to use Linq instead (maybe faster?) for (int i = 0; i < 6; i++) { List<double> coordinateRange = new List<double>(); for (int j = i; j < allCoordinates.Count(); j = j + 6) coordinateRange.Add(allCoordinates[j]); if (i < 3) boundingBox.Add(coordinateRange.Min()); else boundingBox.Add(coordinateRange.Max()); } Any suggestions? Many thanks! Greets!

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• Calculating angle a segment forms with a ray

  - by kr1zz

  I am given a point C and a ray r starting there. I know the coordinates (xc, yc) of the point C and the angle theta the ray r forms with the horizontal, theta in (-pi, pi]. I am also given another point P of which I know the coordinates (xp, yp): how do I calculate the angle alpha that the segment CP forms with the ray r, alpha in (-pi, pi]? Some examples follow: I can use the the atan2 function.

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• 2D Skeletal Animation Transformations

  - by Brad Zeis

  I have been trying to build a 2D skeletal animation system for a while, and I believe that I'm fairly close to finishing. Currently, I have the following data structures: struct Bone { Bone *parent; int child_count; Bone **children; double x, y; }; struct Vertex { double x, y; int bone_count; Bone **bones; double *weights; }; struct Mesh { int vertex_count; Vertex **vertices; Vertex **tex_coords; } Bone->x and Bone->y are the coordinates of the end point of the Bone. The starting point is given by (bone->parent->x, bone->parent->y) or (0, 0). Each entity in the game has a Mesh, and Mesh->vertices is used as the bounding area for the entity. Mesh->tex_coords are texture coordinates. In the entity's update function, the position of the Bone is used to change the coordinates of the Vertices that are bound to it. Currently what I have is: void Mesh_update(Mesh *mesh) { int i, j; double sx, sy; for (i = 0; i < vertex_count; i++) { if (mesh->vertices[i]->bone_count == 0) { continue; } sx, sy = 0; for (j = 0; j < mesh->vertices[i]->bone_count; j++) { sx += (/* ??? */) * mesh->vertices[i]->weights[j]; sy += (/* ??? */) * mesh->vertices[i]->weights[j]; } mesh->vertices[i]->x = sx; mesh->vertices[i]->y = sy; } } I think I have everything I need, I just don't know how to apply the transformations to the final mesh coordinates. What tranformations do I need here? Or is my approach just completely wrong?

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• Object detection in bitmap JavaScript canvas

  - by fallenAngel

  I want to detect clicks on canvas elements which are drawn using paths. So far I have stored element paths in a JavaScript data structure and then check the coordinates of hits which match the element's coordinates. Rendering each element path and checking the hits would be inefficient when there are a lot of elements. I believe there must be an algorithm for this kind of coordinate search, can anyone help me with this?

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• Isometric tile selection

  - by Dylan Lundy

  I'm not all that good with Maths. I'm trying to make a function to convert mouse coordinates into a particular tile in an isometric view. All of the algorithms I have seen so far work with the X & Y axes going diagonal, my game is currently set up like this, and I would like to keep it so. Is there an algorithm so that if the mouse was at the red dot, it would return the coordinates of the tile that it is sitting on? (6,2)

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• Annoying flickering of vertices and edges (possible z-fighting)

  - by Belgin

  I'm trying to make a software z-buffer implementation, however, after I generate the z-buffer and proceed with the vertex culling, I get pretty severe discrepancies between the vertex depth and the depth of the buffer at their projected coordinates on the screen (i.e. zbuffer[v.xp][v.yp] != v.z, where xp and yp are the projected x and y coordinates of the vertex v), sometimes by a small fraction of a unit and sometimes by 2 or 3 units. Here's what I think is happening: Each triangle's data structure holds the plane's (that is defined by the triangle) coefficients (a, b, c, d) computed from its three vertices from their normal: void computeNormal(Vertex *v1, Vertex *v2, Vertex *v3, double *a, double *b, double *c) { double a1 = v1 -> x - v2 -> x; double a2 = v1 -> y - v2 -> y; double a3 = v1 -> z - v2 -> z; double b1 = v3 -> x - v2 -> x; double b2 = v3 -> y - v2 -> y; double b3 = v3 -> z - v2 -> z; *a = a2*b3 - a3*b2; *b = -(a1*b3 - a3*b1); *c = a1*b2 - a2*b1; } void computePlane(Poly *p) { double x = p -> verts[0] -> x; double y = p -> verts[0] -> y; double z = p -> verts[0] -> z; computeNormal(p -> verts[0], p -> verts[1], p -> verts[2], &p -> a, &p -> b, &p -> c); p -> d = p -> a * x + p -> b * y + p -> c * z; } The z-buffer just holds the smallest depth at the respective xy coordinate by somewhat casting rays to the polygon (I haven't quite got interpolation right yet so I'm using this slower method until I do) and determining the z coordinate from the reversed perspective projection formulas (which I got from here: double z = -(b*Ez*y + a*Ez*x - d*Ez)/(b*y + a*x + c*Ez - b*Ey - a*Ex); Where x and y are the pixel's coordinates on the screen; a, b, c, and d are the planes coefficients; Ex, Ey, and Ez are the eye's (camera's) coordinates. This last formula does not accurately give the exact vertices' z coordinate at their projected x and y coordinates on the screen, probably because of some floating point inaccuracy (i.e. I've seen it return something like 3.001 when the vertex's z-coordinate was actually 2.998). Here is the portion of code that hides the vertices that shouldn't be visible: for(i = 0; i < shape.nverts; ++i) { double dist = shape.verts[i].z; if(z_buffer[shape.verts[i].yp][shape.verts[i].xp].z < dist) shape.verts[i].visible = 0; else shape.verts[i].visible = 1; } How do I solve this issue? EDIT I've implemented the near and far planes of the frustum, with 24 bit accuracy, and now I have some questions: Is this what I have to do this in order to resolve the flickering? When I compare the z value of the vertex with the z value in the buffer, do I have to convert the z value of the vertex to z' using the formula, or do I convert the value in the buffer back to the original z, and how do I do that? What are some decent values for near and far? Thanks in advance.

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