目前掌握的情况，支持aprs的车载有garmin3xx和6xx系列等。主要是是支持garmin的协议航点输入，导航仪显示。
查到的数据是：
the pvt record data in the dumb c formats
' 1 datalinkescape (one byte) &h10
' 2 recordtype (one byte) &h33
' 3 length (one byte) &h40 = 64 bytes of data to follow
alt as single ' 4 altitude above wgs 84 ellipsoid (meters)
epe as single ' 8 estimated position error, 2 sigma (meters)
eph as single ' 12 estimated position error, horizontal only (meters)
epv as single ' 16 estimated position error, vertical only (meters)
pfx as integer ' 20 type of position fix
tow as double ' 22 time of week since the beginning of the current week (seconds)
lat as double ' 30 latitude (radians)
lon as double ' 38 longitude (radians)
ve as single ' 46 velocity east (meters/second)
vn as single ' 50 velocity north (meters/second)
vu as single ' 54 velocity up (meters/second)
msl as single ' 58 msl_hght height of wgs 84 ellipsoid above msl (meters)
lsec as integer ' 62 leap_scnds difference between gps and utc (seconds)
wdys as long ' 64 wn_days week days from december 31st, 1989
' 68 checksum (one byte)
' 69 datalinkescape (one byte) &h10
' 70 endtransmission (one byte) &h03
end type ' total bytes
同时我也追踪到了garmin 的输出协议：（这是garmin310输出的数据）
10725401950e39540115068c0a1a6200150739090ea300150ef90e3c5a00151010ce0a1cd3001514b9080c3f0115166a0a19ae00051910100e353a01151e960b222c00151fb60e3a430105ff000000000000ff0000000000003d10031033406c314f43000040400000c040000034420300000000000075b540cdc4047bfe16e13f3b50551ea0eaff3f000000000000000000000000f1425141
用garmin的专用软件可以将这些数据还原成经纬度和时间等参数。
现在的问题是 我如何提取经纬度并且换算出来。看了几天的协议和手册还是没有明白！这里有代码介绍：
http://www.powerbasic.com/support/pbforums/showthread.php?t=24565
