GPS Manager User Manual -- Real-time logging

Real-time logging

Real-time logging

At present there are two variants of the implementation, that will probably be merged in the future. Any receiver sending data in the NMEA 0183 v2.0 standard format can be used with GPSMan and can use any of the two variants. This also applies to Garmin and Lowrance receivers.

Users of Lowrance receivers will want to use the variant for Lowrance. Users of Garmin-defined protocols, either the so-called Garmin protocol , or the Simple Text Output Protocol, should use the variant for Garmin.

Both variants implement some sort of simulator that can be helpful for tests and in getting acquainted with the interface before going to real-time usage.

GPSMan will work with the variant corresponding to the receiver brand selected in the options menu. After changing this option the program must be restarted because different code has to be loaded.

Variant for the Lowrance

This variant was designed and implemented by Brian Baulch (baulchb_at_hotkey.net.au) who has prepared a description of it.

The file exerciser.tcl used for simulation by this variant can be found in the util directory. It must be edited for configuration before use.

Variant for the Garmin

This variant supports the following protocols:

Garmin PVT (position, velocity and time) Data Protocol, which is a part of the Garmin (GRMN/GRMN or Garmin) protocol,
Garmin Simple Text Output Protocol (Text Out), and
part of NMEA 0183 v2.0.

The receiver must be configured to use one of these protocols. On Garmin receivers this is done in the receiver's Interface display under Setup. Not all Garmin receivers support the first two, in which case NMEA 0183 should be selected and the variant for the Lowrance may also be used. If the selected protocol is not supported, either GPSMan knows about that and issues a warning, or there will be no information captured by GPSMan.

Facts that may help in choosing among the available protocols:

Garmin PVT can be used along the rest of the Garmin protocol, meaning that getting and putting other information from/into the receiver can be done while real time logging is on; the receiver will temporarily stop sending logging information while these operation take place -- this may be DANGEROUS if the logging information is crucially needed for navigation; it is the user's responsability not to initiate such operations in these conditions;
both Simple Text and the implemented part of NMEA 0183 are one way protocols: information is only sent from the receiver to GPSMan; this means that it is not possible for GPSMan to check the connection with the receiver: GPSMan will be passively waiting for information to appear on the serial port;
Simple Text carries less information than Garmin PVT (neither EPE, expected position error, nor EPV, expected position vertical error), while NMEA 0183 may carry more information than Garmin PVT; it is difficult to say more than this because there is no complete information on which NMEA sentences (commands) are sent by receivers.

Selecting the protocol in GPSMan is done in the GPSMan's receiver window using the Protocol menu, or the entry with this name of the GPS Receiver menu. The simulator entry will launch a random generator of (somewhat inconsistent) logging data that will be helpful in getting acquainted with the interface before real-time usage.

Controlling the real-time logging is done with the three buttons Get Log/Stop, Record and Animation in the receiver window, or the entries of the GPS Receiver->Real-time track log menu. The first starts and stops the input of logging information, the second launches a window that records that information, and the third starts the animation on the map. These buttons/entries can be actuated independently of each other, but it is obvious that the recording or the animation cannot start or go on if the input has not started or has been stopped. In this way the user may select when to record or when to have the animation.

The control buttons in the recording window and in the animation control window affect only the recording and the animation, respectively, except in what concerns the logging time interval which is the same for the recording and the animation. The minimum value for the time interval depends on the rate at which the receiver sends information. The initial value for it is 2 seconds. The recording window and the animation control window will appear only after the first valid logging information is received, and this means at least 2 seconds from the clicking on the buttons/entries.

The recording window shows several columns with the logging information. These are, from left to right:

number of the fix,
local date and time,
the latitude and the longitude (datum: "WGS 84"),
altitude in metres,
quality of the position fix,
EPE (estimated position error), EPH (expected position horizontal error), EPV (expected position vertical error) in metres,
the 3 coordinates of the velocity vector in metres/second,
the current bearing (CMG, course made good, track made good), true North.

Columns for which there is no information for the very first fix will be hidden automatically. The title of a column is a button that hides the column. This will be wanted for columns that are not being used or needed. The information in a hidden column is not lost and is updated. At any time a hidden column can be shown again by selecting its name from the Show menu.

The Restart button will destroy all the recorded information and restart recording. The Save button saves as text the contents of the columns. This text cannot be re-loaded by GPSMan. To save the information in a format readable by GPSMan the Make TR button should be clicked to create a track, which can then be saved and loaded in the normal way.

The moving map works as the animation for a track described above. The main difference is in the scale that instead of setting the animation speed sets the logging interval.

For the time being there is no automatic loading of background images, a feature present in the variant for the Lowrance.

Real-time logging