scan_nav

Last updated Fri Nov 19 12:59:05 1999

Scan NB ADCP navigation files

1. USAGE

scan_nav control_file

2. DESCRIPTION

This utility scans NB ADCP navigation files, and generates output files with log information, statistic on selected variables and a binary file with variables values, as well as a prepared navigation data file for each ping. See below for the syntax of the control file.

The aim of running scan_nav is to control the integrity of the navigation files, and generate the binary file. The latter can be used later within Matlab with script scan_bin.m. In addition, if data were logged using TRANSECT, prepared navigation data for each ping are saved in a separate file for use during the averaging of ensembles with process.

The log file contains debugging information about configuration GPS quality changes, as well as time with bad navigation. This can be used to edit and fix the navigation files if necessary.

3. PARAMETERS

The control file must contain the following parameters:



scan_nav_type: keyword

Specify with a keyword the type of navigation files to process. This utility has been designed so that it can be extended for different type navigation files. Hence, the first parameter must determine the type in order to select the parameters and options associated to it. Currently implemented types are:



TRANSECT

This type is used to parse navigation files generated by TRANSECT. These contain all NMEA messages as they are output by the navigation device, with in addition TRANSECT lines corresponding to the time at which ADCP pings are saved on disk.



first_day: YYYY/MM/DD

Some NMEA messages do not contain the date. Hence, this parameter is required to synchronize time information with the correct day.

file_list: file

Name of a file containing the successive names of NB ADCP navigation files to scan. This file can contain C-syntax comments.

out_file: file

Root name for generated output files.

4. OPTIONS

In addition to the parameters listed above, the following options are available:



OPTIONS:

This key word can be used to improve the clarity of the control file and specify the beginning of options. It has no effect.

data_stat_options:

This option allows to select which statistics to calculate. Possible keywords are:



time_between_ensemble



time_between_nav_ping



time_increment



nav_travelled_distance



nav_speed_from_pos



nav_course_from_pos



nav_heading



nav_pitch



nav_roll



satellite_number



satellite_hdop



satellite_height



nav_ship_course



nav_ship_speed



end

This keyword is mandatory and terminates the list of selected statistics to perform.

In addition, the keyword ALL will select all the keywords appearing in the above list. To deselect some specific parameters, prefix the undesired keyword with character ! (see

scan_nbr(1) for an example using this feature).

The values of nav_travelled_distance, nav_speed_from_pos and nav_course_from_pos can differ slightly from different architectures. Due to position errors and a high sampling rate of ADCP pings, the first of these parameters can be quite small.

data_flag_options:

Select which flag changes to report in the log file. Possible keywords are:



gps



dgps



end

This keyword is mandatory and terminates the list of selected flags to check.

In addition, the keyword ALL will select all the keywords appearing in the above list. To deselect some specific parameters, prefix the undesired keyword with character !.

nav_messages:

Select which navigation messages to parse. Possible keywords are:



GGA



GLL



HDT



PRDID



RMC



TRANSECT



VTG



ZDA



end

This keyword is mandatory and closes the selected list of NMEA messages to parse.

In addition, the keyword ALL will select all the keywords appearing in the above list. To deselect some specific parameters, prefix the undesired keyword with character !.

WARNING:

Avoid specifying more than one message containing time information, because these do sometime differ slightly. In the case of ZDA and GGA messages, if the latter has a slightly earlier time, the whole date will be set to the next day.


scan_nav_file: file

This option is provided for the case several scans through navigation files is required. Parameter file can refer to a previous scan (out file) in order to synchronize data. This option was implemented for a situation where ship's attitude were saved in a separate file at a high sampling rate and needed to be synchronized to the ping times. Currently, it is obsolete.

skip_nav_lines:

Number of navigation lines to skip when a bad input navigation line is encountered. This is mainly for situations where the navigation device hangs up and needs a reset: time and position information is usually wrong during a couple of seconds (typically 30 to 60 seconds). Hence, the number of line to skip in such a situation will depend on the navigation sampling frequency.

ascii_log

If this option is specified, data saved in the binary file will be saved in addition in ASCII format into the log file. This allows a quick overview over some of the data found in the raw files and can also be used as a debugging information. However, generated files can be very large.

end

This keyword is mandatory and terminates the list of selected options.

5. TIME RANGES

To allow a finer tuning of which pings to scan, the control file must be terminated by a list of time ranges. See time_rng(5) for the syntax of these.

6. OUTPUT FILES

The following files are generated:
file.log - log file
file.sta - statistics
file.bin - binary data
file.out - pre-processed output navigation data
where file correspond to the value of parameter out_file.

7. AUTHOR

Pierre Jaccard, Geophysical Institute, University of Bergen, 1999

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