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POGetting the distance between geographically placed objects
 

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  1. POGetting the distance between geographically placed objects
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    <p>I have an application (cad like editor) in which the user may place a lot of positional nodes (defined by their latitude and longitude). The application needs to tell the user if these nodes are very close together - a common design error is to overlap them. What the app is doing is something rather like ReSharper or CodeRush does in the IDE - parses the project and reports problems. A project may have several thousand of these nodes so testing for overlap becomes exponetially more time consuming as the numbers go. At the moment I am using two for loops to get through the list. </p> <pre><code>for (int i = 0; i &lt; count - 1; i++) { for (int j = i + 1; j &lt; count; j++) { // check the distance between the i and j elements and if less than // a predetermined value report it } } </code></pre> <p>I would like to get the process of identifying these into 'real time' so that the user is told at once in the event that an overlap occurs. The looping is expensive as is the testing of the distance between nodes. Most of the comparisons are wasted of course.</p> <p>I just wonder if there is another way. I have thought about sorting the list by lat and lon and comparing adjacent elements but I suspect that will not work nor necessarily be faster.</p> <p>My other thought is to move the activity to another thread (I really have no experience of using multiple threads) so that the values are being updated - for example storing a reference to nearby nodes in each object. However I can imagine needing to clone the object tree for the background thread so that there is no conflict with the foreground.</p>
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    1. USScruffyDuck
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      1. VTUpMod
    1. COI think this is a math question. Try [Math StackExchange](http://math.stackexchange.com/) and ask how to calculate the distance between two points on the surface of a sphere identified by longitude and latitude.
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    2. CODistance between two points isn't the issue here, its finding all-pair distances that's causing the problem.
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      1. USVanwaril
    3. COThat's right. My application has all the spherical geography algorithms it needs to calculate distance, bearing etc etc.
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      1. USScruffyDuck
 

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