SBET-XTF Merge will parse ASCII SBET files generated by the POSpac software and update the navigation and attitude information in an XTF file logged in Triton Isis. The record that is modified is the POSRAW data logged from the POS/MV during acquisition, therefore Triton Isis must be configured to log that navigation data type during the survey using the Precise Timing setup.
In addition to supplying the normal real-time navigation data to Isis during the survey the POS/MV must be configured to log the needed raw POSpac data for later processing, consult the Applanix POS/MV or POSpac manuals for details.
The output from the application is a new XTF file with an added extension _sbet added to the filename. So 234-1236.xtf becomes 234-1236_sbet.xtf. Normal processing includes updating the following fields:
Latitude, Longitude, Height, Roll, Pitch, Heading
The application includes the ability to add a Z-offset in meters to bring the Ellipsoid height to MLLW.
The application also generates the Triton cache file (.XTF_idx) for faster loading into Triton's new BathyOne application.
Procedure:
Start SBET-XTF Merge:
Click the icon to open the load file dialog:
A normal open file dialog opens, multiple files can be selected:
Click Open:
The .XTF files are loaded one at a time and a new _sbet.XTf file is created. When the progress bar clears all files have been loaded.
Click the "Settings for SBET" Icon:
A dialog box opens allowing you to select the correct SBET (.txt) file:
The SBET parser opens:
Typical ASCII SBET record from the Applanix POSpac application:
*************************************************************************************************************************
POS OUTPUT Utility
Copyright (C) 1997-2008 by Applanix Corporation []
All rights reserved.
**************************************************************************************************************************
Parameter setup:
POSPROC SBET file: C:\Documents and Settings\USER\My Documents\POSPac MMS\JULY27\Mission 1\Proc\sbet_Mission 1.out
Camera mid-exposure event file: C:\Documents and Settings\USER\My Documents\POSPac MMS\JULY27\Mission 1\Extract\event1_Mission 1.dat
Event time shift: 0.000000 sec
Photo ID file:
Photo ID file format: 2 Fields (Time, Photo ID) Format
Offset between PHOTO ID and EVENT file times: 0.000000 sec
Mapping frame datum: WGS84 ; Mapping frame projection : TM;
central meridian = -117.000000 deg;
latitude of the grid origin = 0.000000 deg; grid scale factor = 0.999600:
false easting = 500000.000000 m; false northing = 0.000000 m;
Boresight values: tx = 0.0000 arc min, ty = 0.0000 arc min, tz = 0.0000 arc min.
Lever arm values: lx = 0.0000 m, ly = 0.0000 m, lz = 0.0000 m.
TIME, DISTANCE, EASTING, NORTHING, ELLIPSOID HEIGHT, LATITUDE, LONGITUDE, ELLIPSOID HEIGHT, ROLL, PITCH, HEADING, EAST VELOCITY, NORTH VELOCITY, UP VELOCITY, EAST SD, NORTH SD, HEIGHT SD, ROLL SD, PITCH SD, HEADING SD
(time in Sec, distance in Meters, position in Meters, lat, long in Degrees, orientation angles and SD in Degrees, velocity in Meter/Sec, position SD in Meters)
149917.00355 0.000 383786.373 3731234.004 -34.632 33.71474243 -118.25421797 -34.632 -0.879 4.133 106.606 5.440 -1.707 0.079 0.013 0.014 0.025 0.013 0.013 0.038
<<<<<<<<<<<<<<<<<<<<<<<,
149917.00855 0.029 383786.401 3731233.996 -34.632 33.71474236 -118.25421767 -34.632 -0.881 4.133 106.602 5.440 -1.707 0.076 0.013 0.014 0.025 0.013 0.013 0.038
The useful data starts around line 24 - use the scroll bars in the upper window to view and select the first or second line of data.
Click in the "Parsed Field" window to select the item then the "Field" window to select the data type, then the "Format" window to select the correct units.
Finally hit the "Update: button to check the parsed values are correct. In the example the time in GPS Week seconds has been correctly parsed as (Date Time) 7/27/2009 20:18:55.
Continue with: Latitude (Degrees), Longituide (Degrees), Height (meters), Roll (Degrees), Pitch (Degrees), Heading (Degrees) in each case check that the value makes sense:
The settings for the parser are saved in an .XML file, so providing the format of the SBET file does not change this parser setup only needs performing once.
Hit OK The left window will show "Parser Setup"
You may enter a Z-Offset to be added to the Ellipsoid height in order to bring the height to some local datum; for example MLLW in this case -34.5 meters was used.
Now hit the arrow key "Insert into cache" to start the merge process:
The processing will start after "Parsed Data..." is displayed:
If any of the XTF files are not covered in time by the selected SBET file a message is displayed for each file:
When all possible files have been processed the progress bar will disappear, if any files were not processed a message "Unknown processing failure!" will be displayed.
However processing of the other files will have been completed successfully.
NOTE on processing:
The Z-Value from the POSpac data INCLUDES the heave correction, you must set the heave correction multiplier in the BathMetry processing software to Zero, otherwise "Double Heave" will be applied to the bathy data.