Tracking Analyst:
ArcView provides the Tracking Analyst extension as a method to input time series geolocated points from either Global Position System receivers or models which output geographic point data. Other programs are available to provide displays, but ArcView has two features which make it the utility of choice for bathymetry collected by the INSE . First is the ability to display other data layer concurrent with the GPS track. Second and more important is the capability of Tracking Analyst to handle the ASCII string output from the Trimble GPS receiver. Almost all track display software requires strict adherence to the National Marine Electronics Association, NMEA-0183 format which specifies a maximum length of 88 characters for the broadcast string. In order to monitor the quality of the GPS fix INSE use a Trimble proprietary string which exceeds 96 characters (the actual length depends on the fix location and quality).
e.g. $PTNL,GPGGK,193419.00,032999,4153.85054690,N,12228.36545714,W,2,07,2.3,EHT439.792
Tracking Analyst uses a connection definition file (sample.daf) to determine the format of the incoming geoposition data string and so allows the use of the required data string.
Following is movie clip made using the TrackingAnalyst playback manager.
This is the track as it was collected in the upper portion of the R-Ranch site. It is time compressed as 15 minutes of data are shown in a 30 second clip. Note the different colors for fix types, only fix type 2 (blue) is good data. Tracking Analyst has two limitations which impact the data collection effort. As seen in the video it 'drops' points as the connection database containing the point positions increases in size, especially above 1000 points (just under 17 minutes of data). A second problem not evident in the video is the time lag for the update of the position which increases from 2-3 seconds to 20-40 seconds as the database increases in size above the 1000 point threshold. Below is the complete track for the R-Ranch site. The purple line is the along track path. The pathlines that go off site occur as the GPS receiver calculates a bad fix and reports the location as Canada or South America.
