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POPrecision lost when storing CLLocationDegrees in MySQL
 

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  1. POPrecision lost when storing CLLocationDegrees in MySQL
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    <p>I'm working on a little app that stores <em>Placemarks</em> specified by iOS devices, into a MySQL backend. When a device saves a new <em>Placemark</em>, it is INSERTed into the DB and the newly generated ID is sent back to the client. If another device attempts to save the same <em>Placemark</em>, the server needs to figure out that it already exists in the DB, and instead of INSERTing and generating a new ID, it needs to send back to the client the existing ID for that Placemark.</p> <p>2 <em>Placemarks</em> are the same if they have identical:</p> <ul> <li>name</li> <li>latitude</li> <li>longitude</li> </ul> <p>Therefore the server attempts to identify if the submitted Placemark already exists by issuing </p> <blockquote> <p>SELECT id FROM Placemark WHERE name=x, latitude=y, longitude=x</p> </blockquote> <ul> <li>In iOS, <code>latitude</code> and <code>longitude</code> are in degrees and of type <code>CLLocationDegrees</code> as reported by <code>&lt;CoreLocation&gt;</code></li> <li>In MySQL, <code>latitude</code> and <code>longitude</code> are defined as <code>DOUBLE</code></li> </ul> <p><br> <strong>The problem:</strong> <br>Precision is lost when storing coordinates, for instance: <br><code>latidude</code> of <code>50.09529561485427</code> is stored as <code>50.0952956148543</code> <br><code>longitude</code> of <code>-122.9893130423316</code> is stored as <code>-122.989313042332</code></p> <p><strong>The question:</strong> <br>Can I use a different data type in MySQL so as to store each coordinate intact?</p> <p><strong>Notes:</strong></p> <ul> <li>I can't store coordinates as <code>TEXT</code> or <code>VARCHAR</code> because I need to be able to say <code>SELECT placemarks coordinates BETWEEN x AND y</code>, or perform other arithmetic SELECTs</li> <li>I can't use MySQL's spatial extensions because portability is an issue, and also because to my understanding, spatial data types are very slow when used as keys (and my use case requires SELECT by coordinates)</li> </ul> <p>Any help appreciated</p>
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    1. COAside from your question, entering both coordinates into Google Maps gives me an almost identical location (it's off by a couple of feet). Do you really need that much accuracy?
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      1. USScott Berrevoets
    2. COHi DTs. I recommend closing this question as a duplicate of http://stackoverflow.com/questions/12504208/what-mysql-data-type-should-be-used-for-latitude-longitude-with-8-decimal-places/12504340#12504340 -- you can adapt that answer to your problem with CLLocationDegrees pretty easily. Regards.
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      1. USYawar
    3. CO@Scott Remember, I use those coordinates in my WHERE clauses. They need to remain intact not because I need to identify a Placemark super accurately, but because they are used as keys in subsequent searches.
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