The NAVinXTF tool allows the replacement of the navigation and other numerical data in an XTF file. The navigation is replaced referencing the navigation Date/time in the XTF file to the Date/time in the new ASCII navigation file. The position is time-interpolated as necessary.
Any ASCII text file can be used as the navigation source, this could be from an external navigation computer or from the saved Isis coverage map after smoothing.
IMPORTANT NOTE
You will need a recent version of MODXTF, if your installed version does not have this option you may download the latest MODXTF from this link.
MODXTF is a stand-alone application and can be placed anywhere on you system, you should unzip the file and place MODXTF.EXE and About.dll in a folder, double-click MODXTF.
This was extracted from an XTF file using the ASCII report feature in Isis:
Section 1: Probably the most difficult part of the operation. The way the parser works is based on the Isis non-numeric character method; any non-numeric character is considered to be a delimiter. Concurrent non numeric characters are concatenated; for example in the file above the non-numeric \ separates the Month and the Day in the Date. Between the Date and Time fields there is a comma and two spaces these are considered as one, so in this example there are a total of 8 fields to be parsed. Note that the seconds of time field is read as one value, the decimal point being regarded as a numeric character.
Start NAVinXTF and hit the Browse button:
Browse for the folder containing the navigation file and hit open, the first value in this file is the Month, and it is in the first position in the string, assign it to Position 1 the Description is Month and the Units are Month (1-12)
Hit Add/Replace to accept:
Continue with Position: 2 Description: Day of Month Unit: Day of Month (1-31)
Then add Year, Hour, Minutes, and finally Seconds in Position 6
The next field (7) is the Northing/Lat and units are Decimal Degrees
The final field (8) is the Easting/Longitude and the units are again Decimal Degrees:
Hit OK when finished, NAVinXTF scans the file and shows the Filename, the Line Count (number of unique records in the file and any duplications also the Fix Time Range.
Pay special attention to the Fix Time Range, make sure the values are what you expect!
If there are duplicate records in the file they are ignored, only records with unique positions are used.
If every looks OK you can save all the parser settings by hitting Exit, the import setting are saved in the NavinXTF.ini file, each time NAVinXTF starts it will recover the settings, so unless the format of the navigation file changes you will not have to enter them again:
When you re-start NAVinXTF and hit the Browse button to reload the nav file you should get the same result as above.
Section 2: Hit the browse button and load the XTF file:
Locate the XTF file:
As the file loads NAVinXTF scan the times in the XTF file and checks the time range against the previously loaded navigation file, if this is a single XTF file the navigation may not cover the start and end times, in that case you will see this error:
Look closely at the Date/Time of the XTF and the Date/Time of the navigation data as displayed in the NAVinXTF window, for NAVinXTF to properly interpolate the position the navigation data file must start BEFORE the XTF file and end AFTER, in this case the navigation file starts at 02:56:47.12 but the XTF file starts at 02:56:46.57, close, but no cigar...
For a single ASCII navigation file you may need to add a "dummy" record at the start:
and the end:
Of the navigation file.
However, in a typical survey the navigation computer may have been logging the navigation data continuously. In that case once the parser has been set, all the XTF files that are covered in the time-period of the navigation can be processed at one time; NAVinXTF will allow processing of any number of simultaneously selected XTF files and will process each without intervention, provided the navigation file covers the entire period with an overlap in time at both ends.
Once the navigation and XTF files match up correctly NAVinXTF gives a display of the two files, their start and end times also the type of navigation found in the XTF and the type of sonar data:
Section 3 By clicking the various buttons you can select whether to replace the Ship Position, the Sensor position or both, note that Layback and Sensor depth can also be replaced if this information had been parsed from the original navigation data.
Hit Process
You will have the opportunity to make a backup of the XTF file:
Progress bars will show both for reading of the navigation file and the XTF file:
For a large survey with many XTF files and a single large Navigation file the XTF bars will cycle as each XTF file is processed; the bar for the navigation file will move more slowly.