GPS instrument

Operation

To start there must be a valid starting position represented by the latitude/longitude fields. When a new GPS is instantiated the Latitude and Longitude values are initiated within the range you have set in the General Settings. First time users may find the way of inputting data in these fields a bit awkward in the beginning, but once used to it you will appreciate the "error proof" entry!

Valid values should also be present in all Control Center fields.

After clicking the "Start" button the GPS simulation will start, and NMEA sentences will be sent to the selected output port of the PC, until the "Stop" button is pressed. Note that only those NMEA sentences will be sent that have been checked in the "NMEA sentences" panel. When the Transmit Interval is set to 0.0 the sentences are output as "single shot" each time you click the "Start" button.

All sentences are shown in the I/O Port Monitor as they are output. When logging is ON (toolbar option), the sentences will also be written to the user selected log file.

Clicking the "Stop" button will suspend the operation, until "Start" is clicked again. Clicking the little X top-right will exit the object and save optionally all current values, so that next time the instrument is used it can continue where it stopped. Note: saving is an optional setting in the General Settings.

A short description of each field follows below.

Object Tag

For easy identifying the object in e.g. the Object Explorer.

This is an optional field and can be left blank.

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GPS coordinates

At creating a new GPS object, the Lat and Lon values are initially taken from the Program Settings. After starting the object, the coordinates are then dynamically updated every n second by calculating a new position from parameters like Velocity and Course, and embedded in the appropriate NMEA sentences before transmitting.

n is taken from the Position Update control (see below).

To change the value of either Latitude or Longitude the instrument must not be running.

To change: place the mouse cursor left of the leftmost digit. Then just start typing the new latitude or longitude, the cursor will advance automatically and the value will be automatically formatted. Example: 53° 21.56' N must be entered as 0532156000N.

After clearing, the fields will look like this: " ___° __._____' _".

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Course, Velocity, Altitude

The values for these fields are taken form the Object Control Center and can be dynamically adjusted when this object is at the foreground and visible.

Note that the Course can also be influenced with the Rudder Control.

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UTC Date, Time, Offset

UTC Date and Time as this appears in the appropriate NMEA data.

The user can either choose for the "real" and actual UTC, or can choose to take a faked UTC.

In the latter case the UTC can be manually manipulated.

The method to be used is determined by a setting in the General Settings, NMEA tab.

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GPS Accuracy Parameters

Dilution Of Precision values, Geoidal Separation and number of satellites in view to be embedded in GGA and GSA data.

Note that these can dynamically be adjusted while the object is running!

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Satellites in use

To be used in the GSA sentence. For standard GPS, select satellite number 1 to 32, for WAAS select satellite numbers 33 to 64.

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Magnetic Variation

Here you enter the Magnetic Variation for the RMC sentence. Select Easterly or Westerly variation by clicking E resp. W.

Initially the value is taken from the General Settings. Mind that this setting is also used in the Heading instrument.

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GPS Fix Quality

Set here the GPS fix quality for the GGA sentence.

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Execution Mode

Either select "Normal", "Auto" or "Navigate".

Both Auto and Navigate mode force a dialog window to open, where you are asked to select a waypoint file. A valid waypoint file is a text file containing one $GPWPL sentence for each waypoint. A series of such waypoints is a route that NemaTalker will automatically follow in Auto or Navigate mode.

In Auto and Navigate mode some new controls are enbled:

(Note: XTE and Steer only relevant in Navigate mode)

Ticking the Track Back checkbox will force NemaTalker to sail the route backwards when it has arrived at the last waypoint.

Ticking the Loop checkbox will force NemaTalker to restart the route from the beginning when it has arrived at the last waypoint.

Auto mode

Select "Auto" if you want the simulator to run a predefined route taken from an input text file containing $GPWPL sentences. Such a file could look like this:

$GPWPL,5126.253,N,00334.389,E,1-121021*54

$GPWPL,5125.000,N,00333.283,E,2-121025*55

$GPWPL,5124.925,N,00327.862,E,3-121027*54

$GPWPL,5123.610,N,00323.304,E,4-121031*55

$GPWPL,5122.306,N,00311.994,E,5-121043*50

$GPWPL,5121.742,N,00311.544,E,6-121104*57

The checksum is not necessary. NemaTalker does not check it. You can obtain the file from a route planning program or create it manually with NemaTalker's built-in text editor. The most convenient way however is to use "Waypoint Creator", a free utility that can be downloaded from the Sailsoft website.

During the Auto mode session you can alter Altitude and Velocity with the controls in the Object Control Center, but not the Course, because bearing and range are automatically calculated by the program.

Navigate mode

Opt for "Navigate" if you want to simulate the run of a predefined route, but want to remain in full control by using all controls in the Object Control Center. Observe the difference with the Auto mode: next to the bearing and range to the next waypoint, the simulator also shows the Cross Track Error (XTE) and the direction to steer to correct the error.

Note that in Navigate mode the XTE and RMB sentences also are enabled and can be selected for output.

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NMEA 0183

GPS Sentences

Here you select the sentences you want NemaTalker to output for this instrument.

For most sentences you can also select the desired mode indicator. For GLL, RMC, VTG, XTE and RMB the meaning of the Mode Indicator is, according to the NMEA 0183 specifications, as follows:

A = Autonomous mode

D = Differential mode

E = Estimated (DR) mode

M = Manual Input mode

S = Simulator mode

N = Data not valid

For the GGA sentence in NMEA 0183 version 2.30 and 3.01 (General Settings, NMEA settings tab) the GPS Fix Quality can be set as follows:

0 = invalid

1 = GPS fix (SPS)

2 = DGPS fix

3 = PPS fix

4 = Real Time Kinematic