• Introduction
• Parsing NMEA Sentences
• Google Maps
• Screenshots
• Tile Naming in Google Maps v2.x
• Updates
• License
• MIDlet

Anyway BlueZ to the rescue:

baroque$ hcitool scan Scanning ... 00:0B:24:33:7B:46 TeleTypeBT01 baroque$ sdptool browse 00:0B:24:33:7B:46 Browsing 00:0B:24:33:7B:46 ...

Oops, it's not browseable. Try searching for something common:

baroque$ sdptool search SP Searching for SP on 00:0B:24:33:7B:46 ... Service Name: Serial Port Service RecHandle: 0x10000 Service Class ID List: "Serial Port" (0x1101) Protocol Descriptor List: "L2CAP" (0x0100) "RFCOMM" (0x0003) Channel: 1 Language Base Attr List: code_ISO639: 0x656e encoding: 0x6a base_offset: 0x100

Connect to this service as follows:

baroque$ rfcomm connect 0 00:0B:24:33:7B:46 Connected /dev/rfcomm0 to 00:0B:24:33:7B:46 on channel 1 Press CTRL-C for hangup

Capturing the output just after it boots, yields:

$======================================================== $ 2004. 10. 07 Bluetooth $======================================================== $ $S/W Version(by JCOM) : Jcom_Remote Ver1.26 for BT $NMEA: GPGGA, GPGSV, GPGSA, GPRMC, 9600bps $STATIC_NAV_ENABLED $TRACK_SMOOTH_ENABLED $Waas On $PSRF150,1,*12 at+btname=TeleTypeBT01 $Version 2.3.2-GSW2-2.05.024-C1Prod1.1 $TOW: 206721 $WK: 1339 $POS: 3794287 -415194 5092911 $CLK: 96708 $CHNL:12 $Baud rate: 9600 System clock: 12.277MHz $HW Type: S2AM $Asic Version: 0x23 $Clock Source: GPSCLK $Internal Beacon: None

Parsing NMEA Sentences

baroque$ cat /dev/rfcomm0
$GPGSV,3,2,10,08,35,170,00,04,29,186,00,23,15,068,00,16,10,028,*76
$GPGSV,3,3,10,06,09,321,,29,07,248,*75
$GPRMC,100142,V,5320.0138,N,00614.7191,W,0.000000,0,050805,,*3B

• latitude and longitude: these are represented as 100*degrees + minutes and must be converted to decimal form for the Google calculation below.
• speed: usually returned in knots.
• altitude.
• time: note that this is GPS time not UTC.

private static final double OX = -98.35; // degrees west longitude private static final double OY = 39.5; // degrees north latitude private static final double PIXEL_RATIO = 0.77162458338772; private static double degrees(int zoom) { return (double)PIXELS / (double)(131072 >> zoom); } /** * Given decimal representations of latitude and longitude, * return the magic Google coordinates. * @return a Point containing (x, y) for the map request for * the given zoom factor. */ public static Point getMapOrdinates(double lat, double lon, int zoom) { double z = degrees(zoom); double x = (lon - OX) * PIXEL_RATIO / z; double y = (OY - lat) * z; return new Point((int)Math.floor(x), (int)Math.floor(y)); }

This allows retrieval of the correct map for any given (lat, lon) pair (e.g., http://mt.google.com/mt?x=18176&y=-3535&zoom=2). In order to find the correct point on the map on which to draw the position, it is necessary to find the (latitude, longitude) bounding box of the map. This is achieved by inverting the calculation above:

• inverting for the current position (x, y) gives (lat_min, lon_min)
• inverting for (x+1, y+1) gives (lat_max, lon_max)

/** * Given a magic Google ordinate, return the longitude for * a given zoom. This allows computation of a bounding box * for a particular map, and plotting exact position on it. */ public static double getLongitude(double x, int zoom) { return x * degrees(zoom) / PIXEL_RATIO + OX; } /** * Given a magic Google co-ordinate, return the latitude for * a given zoom. */ public static double getLatitude(double y, int zoom) { return OY - y * degrees(zoom); }

Screenshots

The lefthand screenshot shows a MIDlet running in a J2ME emulator called me4se. Ultimately the MIDlet will run on a sufficiently-capable phone, i.e., one with MIDP-2.0 and JSR-82, such as a Nokia 6600 or a Sony-Ericsson K750i.

The middle screenshot shows the PersonalJava program above except with the new improved map-protocol, v2.5. Under this protocol, tiles are bigger (256x256) and contain more information (e.g., one-way streets).

The righthand screenshot shows the new map-protocol running on the cvm (Personal Profile) on a Zaurus. Although this VM is slower than Jeode, it was used because the new map-protocol uses PNG maps --- a format unsupported by Jeode.

Tile naming in Google Maps v2.x

• The whole world is (0, 0, 17)
• At the next zoom-level, this is divided into four quadrants: (0, 0, 16), (1, 0, 16), (0, 1, 16), (1, 1, 16). (For some reason these aren't contiguous.)
• At the next zoom-level, the rules become obvious:
  • Decrement the zoom-level.
  • Double the x and y ordinates of the parent quadrant.
  • Pick a quadrant, number its four sub-quadrants as above and add their x and y ordinates to those of their parent quadrant.
  For example, to zoom in on the bottom-left of the Eurasian quadrant, (1, 0, 16), use (2*1+0, 2*0 +1, 16-1).

• It seems like v.1 of the Google Maps API is no longer available; it only did the USA and the British Isles anyway.
• The basic MIDlet above is now available here.