63 lines
2.8 KiB
Markdown
63 lines
2.8 KiB
Markdown
Location
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========
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The `Location_t` class is a 2D point, containing a latitude and longitude in integer degrees * 10<sup>7</sup> (source [here](/src/Location.h)).
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This class also provides geographic distance, bearing and offset functions. Furthermore, they all take advantage of the increased precision of the integer coordinates. Other libraries use floating-point coordinates, which have only 6 or 7 significant digits. By using integer math, calculations maintain their original accuracy as long as possible. For example, small distances can be calculated to millimeter accuracy.
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The example program [NMEAaverage.ino](/examples/NMEAaverage/NMEAaverage.ino) shows several techniques for performing 2D calculations.
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### Distance
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To calculate the distance between a pre-determined point and the current fix,
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```
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NeoGPS::Location_t madrid( 404381311L, -38196229L ); // see https://www.google.com/maps/@40.4381311,-3.8196229,6z
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gps_fix fix;
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void loop()
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{
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while (gps.available( gps_port )) {
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fix = gps.read();
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float dist = fix.location.DistanceKm( madrid );
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// or dist = NeoGPS::Location_t::DistanceKm( fix.location, madrid );
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Serial.print( dist );
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Serial.println( F(" km") );
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```
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`DistanceMiles` is also available
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### Bearing
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To calculate the bearing from one point to another (in radians, CW from North),
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```
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float bearing = fix.location.BearingToDegrees( madrid );
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// or bearing = NeoGPS::Location_t::BearingToDegrees( fix.location, madrid );
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```
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Radians is returned by `BearingTo`.
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### Offsetting a Location
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To move a location by a specified distance, in a specified direction,
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```
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float bearing = fix.location.BearingToDegrees( madrid );
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// or bearing = NeoGPS::Location_t::BearingToDegrees( fix.location, madrid );
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// Step 10km closer to the destination
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Location_t next_stop( fix.location );
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next_stop.OffsetBy( bearing, 10 / NeoGPS::Location_t::EARTH_RADIUS_KM );
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```
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Notice that the distance is specified in *radians*. To convert from km to radians, divide by the Earth's radius in km. To convert from miles, divide the miles by the Earth's radius in miles.
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### NeoGPS namespace
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Because the `Location_t` is inside the `NeoGPS` namespace, any time you want to declare your own instance, use any of the constants in that class (anything that requires the `Location_t` name), you must prefix it with `NeoGPS::` (shown above). As with any C++ namespace, you can relax that requirement by putting this statement anywhere after the NeoGPS includes:
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```
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using namespace NeoGPS;
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```
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This technique is used in the **NMEAaverage.ino** sketch.
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However, if you have any other libraries that declare their own `Location_t` (not likely), you could not use the `using` statement. `Time_t` is inside the `NeoGPS` namespace for the same reason: avoiding name collisions.
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