Figure 4—The Roboat determines its location from the ArcTangent of the ratio of the displacements of the two curves shown here.

NMEA ASCII string in output from the GPS.

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0                    1                      2                     3                     4                     5                      6
0123456789012345678901234567890123456789012345678901234567890123456789 ---------------------------------------------------------------------- $GPRMC,145055,V,4453.6083,N,00944.9533,E,000.0,000.0,070399,000.3,E*7F

The individual elements of this string are:

GPRMC            NMEA type of sentence
145055            GPS time of position fix (seconds)
V                        data quality: A = Valid position, V = receiver warning
4453.6083       latitude in degrees, minutes and decimals: "ddMM.mmnn"
N                         latitude N or S hemisphere
00944.9533     longitude in degrees, minutes and decimals: "DddMM.mmnn"
E                         longitude E or W hemisphere
000.0                 speed over ground (knots)
000.0                 course over ground (0-359.9 degrees)
070399            date of position fix "ddmmyy"
000.3                magnetic variation direction
E                       magnetic variation E or W
7F                     checksum byte (= byte1 eor byte2 eor byte3 eor ... byte66)