NavCom Sapphire Rev.J - Manual (Page 346)

Sapphire Technical Reference Manual Rev. J
346
Example:
How to read latitude. Note, the length is 44 00 => 00 44 = 68 bytes.
00000e7ah: 5B 50 56 54 31 42 5D 44 00 6D 06 58 E3 BA 13 25 ; [PVT1B]D.m.Xãº.%
00000e8ah: 8D BC 25 DF 0E 81 54 FE CB 86 18 1D 00 00 0C 70 ; •¼%ß.• Tþˆ.....p
00000e9ah: FF 25 0B CB 08 A2 11 09 07 0F 00 00 00 00 00 00 ; ÿ%.Ë.¢..........
00000eaah: 06 00 00 07 00 00 00 00 00 FF 01 ED FF 19 00 1B ; .........ÿ.íÿ...
00000ebah: 00 01 D0 04 01 0A D0 04 01 0A 00 2A 34 37 45 35 ; ..Ð...Ð....*47E5
00000ecah: 0D 0A ; ..
Latitude = BC 25 DF 0E
The receiver outputs in Little Endian; do a byte swap => 0E DF 25 BC => 249505212
(249505212 / 2048) / 3600 = 33.84131022135416666 degrees
Also, read this byte to get more precision.
Lat/Lon LSB (two four-bit fields, each LSB = 1/32768)
U08
In this case, (x86 & xF0) 10000110 >> Lat is the first four bits or 1000 = 08.
( (249505212 / 2048) + (8 / 32768) ) / 3600 = 33.841310289171005

Height is relative to ellipsoid, scaled to 1/1000 th of a meter, and the geoid-ellipsoid
separation is scaled to 1/1024
th
of a meter. The geoid-ellipsoid separation is calculated
as the ellipsoidal height minus the geoidal height and is a positive number when the
geoid is above the ellipsoid. Altitude is the vertical distance above the ellipsoid or
geoid. It is always stored as height above ellipsoid in the GPS receiver but can be
displayed as height above ellipsoid (HAE) or height above mean sea level (MSL).

For the pseudocode for PVT1B coordinate conversions, refer to Sapphire
Pseudocode for Coordinate Conversions in Appendix A.
2.91.3 Standard Deviations of Latitude, Longitude and Height
The navigation engine maintains an estimate of the PVT position and clock solution
errors in the form of a 4 x 4 covariance matrix generated from navigation solution
measurement residuals and other factors, for example, atmospheric error and dGPS
correction quality. The values here are the square root of the North, East, and Up terms
of this matrix, presented as unsigned 16-bit integers scaled to 1/1024
th of a meter. To
convert to meters, divide by 1024.
2.91.4 PDOP North, East, and Up
These values represent the Position Dilution of Precision (PDOP) in the North, East, and
Up directions, each provided as an unsigned 8-bit integer. The PDOP measures how
strongly the satellite geometry contributes to the navigational fix. When the satellites are
close, the geometry is weak, and the DOP value is high. When the satellites are more
widely separated, the geometry is stronger and the DOP value is low. As a rule of
thumb, a value of less than five or six can be considered as “good”, a value under three,
excellent. Higher values represent weaker geometry.
2.91.5 Velocity North, East, and Up
These indicators display the estimated velocities in the North, East, and Up directions,
output as 24-bit integers scaled to 1/1024
th of a meter per second. To convert to floating
point meters per second, implement the steps in the following list.