USGS MIPS Navedit Documentation

USGS MIPS Navedit Documentation

This program is an XWindows application that allows a user to interactively edit a navigation file. It is used as a pre-processing tool to "clean up" the navigation file of a sidescan sonar image .

Obtaining the navigation file

To obtain a navigation file, select the "Open" item from the file pull-down menu. This will generate a file selection box that can be used to select the desired navigation file.

Once a navigation file is selected, the file will be displayed in Navedit's window. The listing shows the following fields:

  Record Number
  Date
  Time
  Latitude
  Longitude
  Roll
  Pitch
  Heading
  Velocity
  Altitude
  Depth
  Left slant range
  Right slant range
  Lay back

Options in fixing the navigation file

Selecting the "Options" item from the file pull-down menu will allow the user to select any of the following options:

Zero
This option allows the user to zero out any of the fields in the entire navigation file.
Adjust heading
This option allows Navedit to recalculate new heading values for the entire navigation file. These new values can be calculated using one of two methods. The methods are calculating headings from lat/lons and by applying a declination angle. In using the first method, adjustments are made to the heading values based on latitude/longitude differences between records. In the second method, a user supplied declination angle is added to the heading values.
Calculate velocity
This option allows Navedit to recalculate new velocity values for the entire navigation file based on differences between the date/times and latitude/longitude information between records.
Adjust for layback
This option allows Navedit to use layback information to recalculate the latitude/longitude values of the entire navigation file. In other words, the latitude/longitude values in each record are obtained by the ship pulling the sonar device but knowing the layback information (distance that the sonar device is away from the ship) the latitude/longitude values can be adjusted to obtain more precise measurements.
Time Stamp
This option allows the user to time stamp the entire navigation file all at once. This is accomplished by having the user enter a starting date and time along with a time increment. Navedit places this information in the first record and increments the time and places this new date and time into the succeeding records that follow. The default date and time are the values from the first record in the navigation file.

Filter
This option allows the user to filter the following fields:

  Latitude/Longitude
  Roll
  Pitch
  Heading
  Velocity
  Depth
  Left and right slant ranges
  Altitude
  Layback

using a user specified filter size.

Unique latitudes/longitudes
This option allows the user to detect and correct latitude/longitude values that are identical from one record to another. There are two methods that can be used to correct identical lat/lons. The first method is by extrapolating from the last value. The second is by extrapolating from a user selected value.
Copy altitude
This option allows the user to copy the right slant range value to the left slant range value for each record in the file.
Unique dates/times
This option allows the user to detect and correct date/time values that are identical from one record to another. Two methods can be used to correct identical dates/times, extrapolate last value and user selected last value. Selecting the extrapolate last value method allows Navedit to keep track of an average date/time difference between valid records and applies it to each succeeding record. Selecting the user selected last value allows Navedit to interpolate from the first record containing an identical date/time to the last record in the navigation file which will contain the user specified date/time.

These two methods are only used when the last N records in the navigation file contain identical dates/times. In other words, it does not matter which one you select when identical records are found at the beginning of the navigation file. In this case, a simple interpolation is performed from the first record containing an identical date/time to the next record containing a valid date/time.

Showing fields

Selecting the button labeled "Show" allows the user to select what fields will be displayed in the listing. By default, all the fields are selected meaning that all the fields in each record will be shown in Navedit's window.

Using Derive

Selecting the button labeled "Derive" allows the user to specify criteria for any field so that Navedit can highlight those records in the navigation file that does not meet this criteria.

Interpolating records

Selecting the button labeled "Interp" allows the user to interpolate the values of user specified fields from one record to another. The records are tagged when the user highlights them or they are highlighted by the Derive option.

Note, By using Derive to highlight records and Interp to interpolate information between those records, an entire Navigation file can be easily modified.

Editing records

Selecting the button labeled "Edit" allows the user to manually edit the fields of any record.

Deleting records

Selecting the button labeled "Delete" allows the user to delete records from the navigation file.

To delete a record or set of records, either click on the desired record or highlight the records out of the navigation file. Then click on the "Delete" button, clicking on this button will result in a dialog box questioning whether or not you really want to delete the selected records. Note that deleting records modifies the navigation file itself and not the sidescan sonar image. For example, if the navigation file contains 1000 records and its associated sidescan sonar image contains 1000 lines, deleting the last 5 records in the navigation file shortens the actual navigation file whereas the sidescan sonar image still contains 1000 lines. This option should be used with extreme caution.

Exiting Navedit

Selecting the "Exit" item from the file pull-down menu will cause this program to terminate.