Show PDOP, HDOP, and VDOP

[barbeau]

Summary:

PDOP, HDOP, and VDOP are available via NMEA strings.

From http://aprs.gids.nl/nmea/:

$GPGSA

GPS DOP and active satellites

eg1. $GPGSA,A,3,,,,,,16,18,,22,24,,,3.6,2.1,2.23C
eg2. $GPGSA,A,3,19,28,14,18,27,22,31,39,,,,,1.7,1.0,1.335

1 = Mode:
M=Manual, forced to operate in 2D or 3D
A=Automatic, 3D/2D
2 = Mode:
1=Fix not available
2=2D
3=3D
3-14 = IDs of SVs used in position fix (null for unused fields)
15 = PDOP
16 = HDOP
17 = VDOP

Example string from LG G5 w/ Android 6.0.1:

$GNGSA,A,2,67,68,69,79,84,,,,,,,,1.3,1.0,0.8,2*3A

So PDOP is 1.3, HDOP is 1.0, and VDOP is 0.8.

[barbeau]

Note that the above example from the LG G5 that I used when writing the code and for a unit test was actually a $GNGSA (with a "N") sentence, not a $GPGSA (with a "P"). So currently $GNGSA sentences are supported and parsed, but not $GPGSA (N is presumably for a generic GNSS solution, while P is for a GPS solution).

Apparently these two sentence types are slightly different. Here's data from a LG G5 w/ Android 7.0:

$GPGSA,A,3,03,14,16,22,23,26,,,,,,,3.6,1.8,3.1*38
$GNGSA,A,3,03,14,16,22,23,26,,,,,,,3.6,1.8,3.1,1*3B

The "N" sentence appears to have an extra field prior to the * with the value of 1 - the field to the right of the * is the checksum. So, the PDOP, HDOP, and VDOP respectively is 3.6, 1.8, and 3.1, but in the N sentence a comma appears before the *, whereas in the P sentence the checksum appears right after the VDOP without a separating comma.

It seems some devices are using the P sentence format for sentences that start with $GNGSA - or, there is some other reason why the $GNGSA format occasionally looks like the above $GPGSA format (I can't find any documentation on the $GNGSA online - if anyone knows why there is a difference between these two formats, please let me know).

I believe the $GPGSA format is the cause behind crashes I'm seeing with the current release - we're trying to parse the VDOP from the field containing both the VDOP and the * with the checksum:

java.lang.NumberFormatException: Invalid double: "99.0*2B"
	at java.lang.StringToReal.invalidReal(StringToReal.java:63)
	at java.lang.StringToReal.initialParse(StringToReal.java:164)
	at java.lang.StringToReal.parseDouble(StringToReal.java:282)
	at java.lang.Double.parseDouble(Double.java:301)
	at java.lang.Double.valueOf(Double.java:338)
	at com.android.gpstest.util.GpsTestUtil.getDop(GpsTestUtil.java:250)
	at com.android.gpstest.GpsStatusFragment.onNmeaMessage(GpsStatusFragment.java:294)
	at com.android.gpstest.GpsTestActivity$5.onNmeaReceived(GpsTestActivity.java:508)
	at android.location.LocationManager$GpsStatusListenerTransport$1.handleMessage(LocationManager.java:1537)
	at android.os.Handler.dispatchMessage(Handler.java:102)
	at android.os.Looper.loop(Looper.java:148)
	at android.app.ActivityThread.main(ActivityThread.java:7325)
	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

and:

java.lang.NumberFormatException: For input string: "99.0*2B"
	at java.lang.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1306)
	at java.lang.Double.valueOf(Double.java:511)
	at com.android.gpstest.util.GpsTestUtil.getDop(GpsTestUtil.java:250)
	at com.android.gpstest.GpsStatusFragment.onNmeaMessage(GpsStatusFragment.java:294)
	at com.android.gpstest.GpsTestActivity$4.onNmeaMessage(GpsTestActivity.java:490)
	at android.location.LocationManager$GnssStatusListenerTransport$GnssHandler.handleMessage(LocationManager.java:1419)
	at android.os.Handler.dispatchMessage(Handler.java:102)
	at android.os.Looper.loop(Looper.java:154)
	at android.app.ActivityThread.main(ActivityThread.java:6640)
	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)

Other values we're trying to parse from other stack traces include 2.9*22, 0.9*23, and 0.9*2A among others.

The following devices have the above stack traces (vast majority is java.lang.NumberFormatException: ... at java.lang.StringToReal.invalidReal(StringToReal.java:63):

• Android 6.0 25 61.0%

• Android 4.4 10 24.4%

• Android 5.0 4 9.8%

• Android 5.1 2 4.9%

• Galaxy S5 (klte) 3 7.3%

• MeMO Pad 7 (ME176C) (K013) 5 12.2%

• Galaxy Note3 (hlte) 2 4.9%

• Galaxy Tab Pro 8.4 (mondrianwifi) 1 2.4%

• Galaxy S6 (zeroflte) 1 2.4%

• Galaxy A8 (a8hplte) 1 2.4%

• Galaxy S6 Edge+ (zenlte) 1 2.4%

• Galaxy S7 Edge (hero2lte) 12 29.3%

• L-01F (g2) 1 2.4%

• Galaxy A3(2016) (a3xelte) 1 2.4%

• Galaxy Grand Prime (grandprimeve3g) 2 4.9%

• Galaxy TabS 10.5 (chagallwifi) 2 4.9%

• SHIELD Tablet (shieldtablet) 1 2.4%

• Lenovo YOGA Tablet Pro-1050L/Yoga Tablet 2 (YT2) 1 2.4%

• Zenfone 3 (ASUS_Z012D) 1 2.4%

• Galaxy Note2 (t0lte) 1 2.4%

• Galaxy Note4 (trelte) 1 2.4%

• Galaxy S7 (herolte) 3 7.3%

• Galaxy Note Edge (tblte) 1 2.4%

[barbeau]

Closed via 2528122.