GPS数据格式

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GPS 数据格式

GPS 抖动检测：

关于车辆管理的软件。发现当车辆静止时，GPS接收器收到的数据、方向、速度都在不停的跳动，从而造成车子停止时，车子在地图上不停的乱跳的现象。

GPS 最后的 *后面的两个字符为校验和，其计算方式为从$到*之间所有字符的XOR值（不包括$和*）：

function Checksum(const s: string): string;

var

sum: Byte;

i : Integer;

begin

sum := Ord(s[2]);

for i := 3 to Length(s) - 1 do

sum := sum xor ord(s[i]);

Result := IntToHex(sum, 2);

end;

function Test(): string;

begin

//$GPGGA,041147.000,2214.6493,N,11334.9579,E,1,07,1.0,7.8,M,-3.8,M,,0000*4F

Result := Checksum('$GPGGA,041147.000,2214.6493,N,11334.9579,E,1,07,1.0,7.8,M,-3.8,M,,0000*');

end;

这里谈一些解决方法或这方面的资料。

普通GPS误差+/-10m，不乱跑是不正常的

一般的解决办法是读NMEA数据中的速度值为零时，就不去更新地图上的经纬度。如果你的速度和经纬度都是在不断地微动（早期的SurF板就一直解决不了这个问题），那就没办法了。

几个老问题，硬件的因素不好控制，目前还是软件判断做补救工作：

1.检测到的状态为静止时，强制速度为0；

2.速度为0时，强制方向为0；

3.至于漂移问题，可以通过比较上次定位数据的经纬度差的绝对值（同时包括时间）来判定；

至于纯硬件问题，有的模块漂移100m都是可能的

要解决得硬件配合

1、若有行车记录仪检测到车速就能精确解决；

2、或者当车熄火时，硬件定位仪应能检测的到，根据熄火状态去漂移

就目前来看，静态漂移很难完全避免

从硬件的角度，选择好的接收板；从软件的角度，单纯从速度、位置的瞬时值肯定很不好判断。GPS每秒更新数据，而物体的运动轨迹一般是连续的而不是杂乱无章的，状态的变化一般是渐渐的，而不是突变。可以考虑连续的几个瞬时值的变化过程。

建议从以下两个方面综合判断

1.方向的变化：

方向变化过于频繁，一会左转一会右转，一会向东，一会向西，基本上是漂移。正常行驶很少见方向频繁的不连续变化的。

2.位置的变化

在1秒之内，两个位置之间的距离达到50米以上(180KM/H)，对于汽车和轮船基本上有问题，当然，飞机除外。

如果是车载，可以根据速度判断，静态漂移速度值一般不会大于5km/h。

从硬件的角度看，有的gps模块是可以判断是否是在静漂状态的

目前，如果卫星漂移会造成一些问题，开发的轨迹回放是把数据库中的速度为0的过滤掉，这样就没有问题了

Simple Text Output Format:

The simple text (ASCII) output contains time, position, and velocity data in the fixed width fields (not delimited) defined in the following table:

FIELD DESCRIPTION: WIDTH: NOTES:

----------------------- ------- ------------------------

Sentence start 1 Always '@'

----------------------- ------- ------------------------

/Year 2 Last two digits of UTC year

| ----------------------- ------- ------------------------

| Month 2 UTC month, "01".."12"

T | ----------------------- ------- ------------------------

i | Day 2 UTC day of month, "01".."31"

m | ----------------------- ------- ------------------------

e | Hour 2 UTC hour, "00".."23"

| ----------------------- ------- ------------------------

| Minute 2 UTC minute, "00".."59"

| ----------------------- ------- ------------------------

\Second 2 UTC second, "00".."59"

----------------------- ------- ------------------------

/Latitude hemisphere 1 'N' or 'S'

| ----------------------- ------- ------------------------

| Latitude position 7 WGS84 ddmmmmm, with an implied

| decimal after the 4th digit

| ----------------------- ------- ------------------------

| Longitude hemishpere 1 'E' or 'W'

| ----------------------- ------- ------------------------

| Longitude position 8 WGS84 dddmmmmm with an implied

P | decimal after the 5th digit

o | ----------------------- ------- ------------------------

s | Position status 1 'd' if current 2D differential GPS position

i | 'D' if current 3D differential GPS position

t | 'g' if current 2D GPS position

i | 'G' if current 3D GPS position

o | 'S' if simulated position

n | '_' if invalid position

| ----------------------- ------- ------------------------

| Horizontal posn error 3 EPH in meters

| ----------------------- ------- ------------------------

| Altitude sign 1 '+' or '-'

| ----------------------- ------- ------------------------

| Altitude 5 Height above or below mean

\ sea level in meters

----------------------- ------- ------------------------

/East/West velocity 1 'E' or 'W'

| direction

| ----------------------- ------- ------------------------

| East/West velocity 4 Meters per second in tenths,

| magnitude ("1234" = 123.4 m/s)

V | ----------------------- ------- ------------------------

e | North/South velocity 1 'N' or 'S'

l | direction

o | ----------------------- ------- ------------------------

c | North/South velocity 4 Meters per second in tenths,

i | magnitude ("1234" = 123.4 m/s)

t | ----------------------- ------- ------------------------

y | Vertical velocity 1 'U' (up) or 'D' (down)

| direction

| ----------------------- ------- ------------------------

| Vertical velocity 4 Meters per second in hundredths,

\ magnitude ("1234" = 12.34 m/s)

----------------------- ------- ------------------------

Sentence end 2 Carriage return, '0x0D', and

line feed, '0x0A'

----------------------- ------- ------------------------

If a numeric value does not fill its entire field width, the field is padded

with leading '0's (eg. an altitude of 50 meters above MSL will be output as "+00050").

Any or all of the data in the text sentence (except for the sentence start

and sentence end fields) may be replaced with underscores to indicate

invalid data.

GPS 解码函数，NMEA0183解码函数：

const

CIMaxSatInfo = 4;

type

TSatInfo = packed record /// GPS信息

PRN: integer; // 卫星号码

EL,AZ: integer; // 仰角、方位

SN: integer; // 信号噪音比

end;

TGPSInfo = packed record /// 解码后的GPS信息结构

UTCTime: TDateTime; /// GPS时间, UTC 格式，不包含日期

Longitude : Double; /// 经度

Latitude : Double; /// 纬度

LatHemi, LonHemi: Char;// N、S、E、W

Altitude : Double; /// 海拔高度

Speed : Double; /// 速度

Course: Double; /// 方向

Fix: string[10]; /// 定位方式

SatInfo: Array [1..CIMaxSatInfo] of TSatInfo;

end;

TGPSTimePoint = packed record /// GPS 三参数组：时间，经度，纬度

Time: TDateTime;

Longitude: Double;

Latitude: Double;

end;

/// GPS移动方向，八个方向

TDirection = (gdNone, gdW2E, gdE2W, gdS2N, gdN2S, gdES2WN, gdWS2EN, gdWN2ES, gdEN2WS);

// [2007-9-13]Kingron: 解码GPS数据，NMEA0183格式，每次一条信令，非连续

// 处理GPS发来的所有数据

//$PGRME,45.3,M,,M,45.3,M*00

//Estimated Error Information (PGRME)

//The GARMIN Proprietary sentence $PGRME reports estimated position error

//information.

//$PGRME,<1>,M,<2>,M,<3>,M*hh<CR><LF>

//<1> Estimated horizontal position error (HPE), 0.0 to 999.9 meters

//<2> Estimated vertical position error (VPE), 0.0 to 999.9 meters

//<3> Estimated position error (EPE), 0.0 to 999.9 meters

//下面是一些样本数据

//$GPGSV,3,1,09,05,18,043,43,11,04,290,44,14,59,034,43,15,01,184,*70

//$GPGSV,3,2,09,16,13,200,,18,22,153,,23,44,160,,25,54,288,51*7E

//$GPGSV,3,3,09,30,46,061,30,,,,,,,,,,,,*45

//$PGRME,45.3,M,,M,45.3,M*00

//$GPRMC,131558,A,2818.7145,N,10944.4235,E,000.0,000.0,1n0503,002.0,W*61

//$GPGGA,131558,2818.7145,N,10944.4235,E,1,04,4.6,238.2,M,-25.4,M,,*66

//$GPGSA,A,2,05,11,14,,,,,25,,,,,4.6,4.6,*1A

function DecodeGPS(const msg: string; var GPSInfo: TGPSInfo): Boolean;

function GetNextItem(start: integer; len: integer; var tmp: string):integer;

var

i: integer;

begin

tmp := '';

result := 0;

i := start + 1;

while (msg[i] <> '$') and (msg[i] <> ',') and (msg[i] <> '*') and (i<Len) do begin

tmp := tmp + msg[i];

inc(i);

inc(result);

end;

function CountChar(start: integer; len: integer):integer;

var

i: integer;

begin

i:=start;

Result := 0;

while (msg[i] <> Chr($0d)) and (msg[i] <> Chr($0a)) and (msg[i] <> '$') and (i<Len) do begin

if msg[i] = ',' then inc(Result);

inc(i);

end;

var

CurPos,strLen: integer;

tmpStr: string;

tmpFloat: Double;

tmpi,i: integer;

begin

CurPos := 0;

strLen := Length(msg);

while CurPos<strLen do begin

while (msg[CurPos] <> '$') and (CurPos<strLen) do inc(CurPos);

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

if tmpStr = 'GPGGA' then begin

if CountChar(CurPos,strLen) = 14 then begin

//$GPGGA,131558,2818.7145,N,10944.4235,E,1,04,4.6,238.2,M,-25.4,M,,*66

//$GPGGA,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,M,<10>,M,<11>,<12>*hh<CR><LF>

//<1> UTC时间, hhmmss

//<2> 纬度, ddmm.mmmm (输出前导零)

//<3> 南北, N or S

//<4> 经度, dddmm.mmmm (输出前导零)

//<5> 东西, E or W

//<6> GPS质量评估, 0 = 不能定位, 1 = 非差分定位

//, 2 = 差分定位(DGPS), 6 = 估计

//<7> 使用中的卫星数量, 00 to 12 (输出前导零)

//<8> Horizontal dilution of precision, 0.5 to 99.9

//<9> 海拔高度, -9999.9 to 99999.9 米

//<10> Geoidal height, -999.9 to 9999.9 meters

//<11> 差分GPS(RTCM SC-104)数据寿命, number of seconds since last valid

//RTCM transmission (非差分时为空)

//<12> 差分GPS参考站ID, 0000 to 1023 (输出前导零,非差分时为空)

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

GPSInfo.UTCTime := MyTimeToStr(tmpStr, GPSInfo.UTCTime);

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

tmpFloat := StrToFloatDef(tmpStr,0) / 100;

GPSInfo.Longitude := Int(tmpFloat) + (Frac(tmpFloat) * 5) / 3;

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

GPSInfo.LatHemi := tmpStr[1];

if GPSInfo.LatHemi = 'S' then GPSInfo.Latitude := -1 * GPSInfo.Latitude;

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

tmpFloat := StrToFloatDef(tmpStr,0) / 100;

GPSInfo.Longitude := Int(tmpFloat) + (Frac(tmpFloat) * 5) / 3;

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

GPSInfo.LonHemi := tmpStr[1];

if GPSInfo.LonHemi = 'W' then GPSInfo.Longitude := -1 * GPSInfo.Longitude;

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

GPSInfo.Altitude := StrToFloatDef(tmpStr,0);

end;

end else if tmpStr = 'GPGSA' then begin

if CountChar(CurPos,strLen) = 17 then begin

//卫星状态表

//$GPGSA,A,2,05,11,14,,,,,25,,,,,4.6,4.6,*1A

//$GPGSA,<1>,<2>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<3>,<4>,<5>,<6>

//*hh<CR><LF>

//<1> Mode, M = manual, A = automatic

//<2> 定位状态, 1 = not available, 2 = 2D, 3 = 3D

//<3> 卫星号码，最多12个

//<4> Position dilution of precision, 0.5 to 99.9

//<5> Horizontal dilution of precision, 0.5 to 99.9

//<6> Vertical dilution of precision, 0.5 to 99.9

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

case StrToIntDef(tmpStr,0) of

2: GPSInfo.Fix := '2D Fix';

3: GPSInfo.Fix := '3D Fix';

else

GPSInfo.Fix := 'No Fix';

end;

end else if tmpStr = 'GPRMC' then begin

if CountChar(CurPos,strLen) = 11 then begin

//Recommended Minimum Specific GPS/TRANSIT Data (RMC)

//$GPRMC,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>*hh<CR><LF>

//$GPRMC,131558,A,2818.7145,N,10944.4235,E,000.0,000.0,1n0503,002.0,W*61

//<1> UTC time of position fix, hhmmss format

//<2> Status, A = Valid position, V = NAV receiver warning

//<3> Latitude, ddmm.mmmm format (leading zeros will be transmitted)

//<4> Latitude hemisphere, N or S

//<5> Longitude, dddmm.mmmm format (leading zeros will be transmitted)

//<6> Longitude hemisphere, E or W

//<7> Speed over ground, 000.0 to 999.9 knots (leading zeros will be transmitted)

//<8> Course over ground, 000.0 to 359.9 degrees, true (leading zeros will be

//transmitted)

//<9> UTC date of position fix, ddmmyy format

//<10> Magnetic variation, 000.0 to 180.0 degrees (leading zeros will be transmitted)

//<11> Magnetic variation direction, E or W (westerly variation adds to true course)

//<12> Mode indicator (only output if NMEA 2.30 active), A = Autonomous, D =

//Differential, E = Estimated, N = Data not valid

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

GPSInfo.Speed := StrToFloatDef(tmpStr,0);

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

GPSInfo.Course := StrToFloatDef(tmpStr,0);

end;

end else if tmpStr = 'GPGSV' then begin

if CountChar(CurPos,strLen) = 19 then begin

//$GPGSV,3,1,09,05,18,043,43,11,04,290,44,14,59,034,43,15,01,184,*70

//$GPGSV,3,2,09,16,13,200,,18,22,153,,23,44,160,,25,54,288,51*7E

//$GPGSV,3,3,09,30,46,061,30,,,,,,,,,,,,*45

//$GPGSV,<1>,<2>,<3>,<4>,<5>,<6>,<7>,...<4>,<5>,<6>,<7>*hh<CR><LF>

//<1> Total number of GSV sentences to be transmitted

//<2> Number of current GSV sentence

//<3> Total number of satellites in view, 00 to 12 (leading zeros will be transmitted)

//<4> Satellite PRN number, 01 to 32 (leading zeros will be transmitted)

//<5> 卫星仰角, 00-90度

//<6> 卫星方位角, 000-359度

//<7> 卫星信号噪音比 00-99db

//NOTE: Items <4>,<5>,<6> and <7> repeat for each satellite in view to a maximum of

//four (4) satellites per sentence. Additional satellites in view information must be

//sent in subsequent sentences. These fields will be null if unused.

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

tmpi := StrToIntDef(tmpStr,1);

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

for i:= 1 to CIMaxSatInfo do begin

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

GPSInfo.SatInfo[(tmpi-1)*4 + i].PRN := StrToIntDef(tmpStr,0);

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

GPSInfo.SatInfo[(tmpi-1)*4 + i].EL := StrToIntDef(tmpStr,0);

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

GPSInfo.SatInfo[(tmpi-1)*4 + i].AZ := StrToIntDef(tmpStr,0);

CurPos:= CurPos + 1 + GetNextItem(CurPos,strLen,tmpStr);

GPSInfo.SatInfo[(tmpi-1)*4 + i].SN := StrToIntDef(tmpStr,0);

end;

inc(CurPos);

end;

Result := True;

end;

GPS.rar (211.7KB)