Novatel OM-20000041 用户手册

3

Data Logs

MiLLennium GPSCard Software Version 4.50 Command Descriptions Manual Rev 1

37

The 

NMEA

 log structures follow format standards as adopted by the National Marine Electronics Association. The

reference document used is "Standard For Interfacing Marine Electronic Devices 

NMEA

 0183 Version 2.00". For

further information, see Appendix F, Standards and References, Page 233. The following table contains excerpts
from Table 6 of the 

NMEA

 Standard which defines the variables for the 

NMEA

 logs. The actual format for each

parameter is indicated after its description.

All logs report 

GPS

 time expressed in 

GPS

 weeks and seconds into the week. The time reported is not corrected for

local receiver clock error. To derive the closest 

GPS

 time, one must subtract the clock offset shown in the 

CLKA

 log

(field 4) from 

GPS

 time reported.

Status

A

Single character field:
A = Yes, Data Valid, Warning Flag Clear
V = No, Data Invalid, Warning Flag Set

Latitude

llll.ll

Fixed/Variable length field:
degrees|minutes.decimal - 2 fixed digits of degrees, 2 fixed digits of minutes and a variable number of 
digits for decimal-fraction of minutes.  Leading zeros always included for degrees and minutes to 
maintain fixed length.  The decimal point and associated decimal-fraction are optional if full resolution 
is not required.

Longitude

yyyyy.yy

Fixed/Variable length field:
degrees|minutes.decimal - 3 fixed digits of degrees, 2 fixed digits of minutes and a variable number of 
digits for decimal-fraction of minutes.  Leading zeros always included for degrees and minutes to 
maintain fixed length.  The decimal point and associated decimal-fraction are optional if full resolution 
is not required 

Time

hhmmss.ss

Fixed/Variable length field:
hours|minutes|seconds.decimal - 2 fixed digits of hours, 2 fixed digits of minutes, 2 fixed digits of 
seconds and variable number of digits for decimal-fraction of seconds.  Leading zeros always included 
for hours, minutes and seconds to maintain fixed length.  The decimal point and associated decimal-
fraction are optional if full resolution is not required.

Defined field

Some fields are specified to contain pre-defined constants, most often alpha characters.  Such a field is 
indicated in this standard by the presence of one or more valid characters.  Excluded from the list of 
allowable characters are the following which are used to indicate field types within this standard:
"A", "a", "c", "hh", "hhmmss.ss", "llll.ll", "x", "yyyyy.yy"

Variable 
numbers

x.x

Variable length integer or floating numeric field.  Optional leading and trailing zeros.  The decimal point 
and associated decimal-fraction are optional if full resolution is not required (example: 73.10 = 73.1 = 
073.1 = 73)

Fixed HEX field

hh___

Fixed length HEX numbers only,  MSB on the left

Variable text

c--c

Variable length valid character field.

Fixed alpha field

aa___

Fixed length field of uppercase or lowercase alpha characters

Fixed number 

xx___

Fixed length field of numeric characters

Fixed text field

cc___

Fixed length field of valid characters

1.

Spaces may only be used in variable text fields.

2.

A negative sign "-" (HEX 2D) is the first character in a Field if the value is negative.  The sign is omitted if value is positive.

3.

All data fields are delimited by a comma (,).

4.

Null fields are indicated by no data between two commas (,,).  Null fields indicate invalid or no data available.

5.

The NMEA Standard requires that message lengths be limited to 82 characters.