Garmin GPS 16-HVS Instruction Manual - Page 15

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A.1.3 Filters

Filters can be used to make sure P15 reads the correct data string. Filters also

ensure P15 starts to read the string at the beginning of the string. To use a

filter, follow P15 with instruction P63 (extended parameters). P63 is used to

define the filter. Enter the desired filter in P63.

ASCII Equivalent

A.1.4 Managing the Data

Several of the data values in the $GPGGA string are too large to view or write

to final storage. Some simple math is used to parse the data.

The UTC time is in the format hhmmss where hh is the hours, mm is the

minutes and ss is the seconds. Six digits are too many to view with the

datalogger display and some software. Add 0.3 to the raw time field. Multiply

the raw time input location by 0.01 to reduce the magnitude and place the

seconds in the fractional portion of the number. Next use P45 to write the

integer portion (hours/minutes) to a new input location, then use P44 to write

the fractional portion to another input location (seconds) and multiply that

location by 100. The last step is to use P45 again to take the integer portion of

the input location for seconds. The result is hour/minutes in one input location

and seconds in another.

The latitude and longitude can be parsed with the P15 instruction when decimal

delimiter is on. If P15, parameter 2 is 6x, where the x selects the baud rate,

every non-numeric value and decimal point will act as a delimiter. The

Degrees and Minutes will be placed in one input location, and the minute

fractional portion will be placed in the next input location. The decimal

delimiter preserves the resolution of the original measurement.

Further parsing of the latitude and longitude may be necessary. Longitude

degrees and minutes can range in value up to 18059, which exceeds the low

resolution format of the dataloggers final storage area. Either parse the latitude

and longitude degrees and minutes the same way the time was parsed, or store

the data in high-resolution format.

The GPS quality number can be used to determine if you have a valid GPS fix

and if the datalogger received the data properly. Use P89 to test if the GPS

quality number is greater than or equal to one. There is a catch to using the

GPS quality number to verify your data. P15 will write to fifteen input

locations if everything works correctly. If P15 fails to read the GPS data, only

the first input location is written to. The GPS quality number will be

unchanged. If P15 fails to read the GPS data, the value displayed in the first

input location will be 99999. The datalogger actually stores FFFFFFFFh, a

very large number. The time field includes six digits, which can be greater

than 99999. This limits the usefulness of the time field as a test for a valid

TABLE A-2. Filter

Character

Appendix A. CR23X/CR10X Programs

A-3