65 lines
2.4 KiB
Markdown
65 lines
2.4 KiB
Markdown
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Character-oriented methods
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===========================
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Sometimes, individual characters or sentences must be processed or filtered, long before a fix structure is completed (i.e., `available()`). In this advanced technique, your sketch should read each character and pass it to the character-oriented method `gps.decode()`:
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```
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void loop()
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{
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while (serial.available()) {
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char c = serial.read();
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if (gps.decode( c ) == DECODE_COMPLETED) {
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... do something with gps.fix()...
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}
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```
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As `gps` decodes those bytes, it will gradually fill out the pieces of its internal fix structure, `gps.fix()` (members described [here](Data%20Model.md). When you want to use some of the fix data, you can access it like this:
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```
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Serial.print( gps.fix().latitude() );
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Serial.print( ',' );
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Serial.println( gps.fix().longitude() );
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```
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However, you must wait for the sentence to be completely decoded. You can't access `gps.fix()` unless you know that it is COMPLETED. You must copy it to another fix variable if you need to access it at any time.
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**IMPORTANT:** `gps.fix()` **IS ONLY VALID WHEN:**
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- `gps.decode()` just returned `DECODE_COMPLETED`, or
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- `gps.is_safe()`
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This is because `gps.fix().speed` may be half-formed. You must either do all your accessing immediately after `gps.decode()` returns `DECODE_COMPLETED`:
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```
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void loop()
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{
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// At this point of the code, speed could be half-decoded.
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if (gps.fix().speed <= 5) // NOT A GOOD IDEA!
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Serial.println( F("Too slow!") );
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while (serial.available()) {
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char c = serial.read();
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if (gps.decode( serial.read() ) == NMEAGPS::DECODE_COMPLETED) {
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// Access any piece of gps.fix() in here...
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if (gps.fix().speed <= 5) // OK!
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Serial.println( F("Too slow!") );
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if (gps.fix().lat ...
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}
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}
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```
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Or you must call `gps.is_safe()` before using `gps.fix()`. It is safest to copy `gps.fix()` into your own variable for use at any time:
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```
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gps_fix my_fix;
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void loop()
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{
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while (serial.available()) {
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char c = serial.read();
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if (gps.decode( serial.read() ) == NMEAGPS::DECODE_COMPLETED) {
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my_fix = gps.fix(); // save for later...
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}
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}
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if (my_fix.speed <= 5) // OK
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DigitalWrite( UNDERSPEED_INDICATOR, HIGH );
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```
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Although the character-oriented program structure gives you a finer granularity of control, you must be more careful when accessing `gps.fix()`.
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