Ellipsoidal Height = Mean Sea Level (MSL) Height + Undulation Equation: h = H +N If N = 0; then h = H; User can alter the height output to become ellipsoidal height by changing the undulation value (N) use by the receiver. When setting the undulation value to zero, the output MSL height will equal ellipsoidal height. Here is the command:
UNDULATION USER 0
============= OEM4 Firmware =============
User can only fix the position of the receiver by using Lat-Long coordinates and height in MSL. The undulation used for this fix position MSL height is from factory default. The factory default for undulation is TABLE, which is the internal undulation table (same as OSU89B). It is best to first determine the TABLE undulation value for the base receiver fix position and then subtract the TABLE undulation from known ellipsoid height to enter as MSL height (H = h-N). Following the recommended steps below, the height above MSL from BESTPOS or the antenna altitude from the GGA logs at the base receiver should equal the known ellipsoidal height. Please ensure the UNDULATION is set to TABLE when issuing FIX POSITION.
1) Set UNDULATION TABLE
2) Use FIX POSITION to fix the base receiver position
3) Log GPGGA or BESTPOS to determine the TABLE undulation value for this lat-long coordinates (ref WGS84)
4) Subtract the TABLE undulation value from the base receiver's known ellipsoidal height (H = h-N).
5) Enter the new computed MSL height (H) with the lat-long coordinates to fix the base receiver position 6) Issue command UNDULATION USER 0 for BESTPOS or GGA logs to output ellipsoidal heights
============= OEMV Firmware =============
User can fix the position of the receiver by using Lat-Long coordinates and height in MSL or ellipsoidal. The UNDULATION and FIX commands are no longer order dependent on the OEMV firmware. The factory default for the fix position height is same as in the OEM4 firmware, height is assumed to be entered in MSL. To fix position in the ellipsoidal height:
1) Set UNDULATION USER 0
2) Enter FIX POSITION lat long hgt (hgt is ellipsoidal height)
3) Issue SAVECONFIG Please note: - Once the undulation value is set to zero, the output MSL height in BESTPOS or GGA logs will equal ellipsoidal height. - Fixing the base unit's position with ellipsoidal height will not affect RTK computations between base and rover. - The rover output height will remain as factory default in MSL.
Please contact NovAtel Customer support if further assistance is needed. Email: firstname.lastname@example.org U.S. & Canada: 1-800-NovAtel