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3 Data Logs
38 MiLLennium GPSCard SW Version 4.503/4.52 Command Descriptions Manual Rev 2
3.4 NMEA FORMAT DATA LOGS
General
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 239. 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.
3.5 GPS TIME VS. LOCAL RECEIVER TIME
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
Field Type Symbol Definition
Special Format Fields
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"
Numeric Value Fields
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
Information Fields
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
NOTES:
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.