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Using StormPredator with GPS
 
 
GPS Overview:

This feature will allow you to connect any NMEA compliant GPS device to your computer via USB or serial port that conforms to NMEA data standards (that includes virtually all modern GPS units). The live GPS position indicator is selectable and will change as you move on the map. Successful operation of this feature assumes that you have chosen a radar location that is in proximity with your current physical location.

StormPredator has been tested with several commercial GPS devices that support the NMEA communications protocol. If you have a GPS device, check the manual to see if it offers live data via a USB port or serial (COM) port. Chances are you will be able to make it work with StormPredator.

If you don't have a GPS device, many low cost USB enabled models are available, many are under $100. StormPredator also offers a "ready to run" GPS unit at our website for purchase separately for or as a bundle with the StormPredator Version 3.5 program.

Here is what the preferred USB enabled GPS device that we offer for sale looks like:

It features a magnetic base and waterproof operation for ease of use on the rooftop or dashboard of a vehicle. For details on this GPS unit or to purchase it, please click here. You'll see a description there and option to buy the GPS unit shown above.

You should install your GPS device on your PC with whatever drivers the manufacturer may provide with the unit. Many units (including the one offered by StormPredator.com) have a Windows utility program to test operation prior to use with other programs. If you use such a program, be sure to note what COM port number the GPS has been assigned to on your PC, and if the data communications parameters are set to anything besides the common default of 4800, 8,N,1.

Some GPS units may conflict with other previously installed USB to Serial port bridge devices and/or drivers. Be sure to check your manufacturers troubleshooting guide for such issues if they occur. StormPredator support cannot assist you in connecting a GPS unit (other than one purchased from StormPredator.com ) since we can't possibly be versed with the dozens of different brands and the device drivers that are currently available.

Follow the manufacturer's suggestions for operation. Generally, GPS units will not work indoors or if they do, perform poorly. Testing GPS operation is best done outside with a laptop and a clear view of the Southern sky.


Understanding GPS Operation in StormPredator

StormPredator supports mobile GPS devices that are connected to the computer via a USB or serial port. The standard default baud rate of 4800 Baud, 8 bits, no parity bit, and 1 stop bit (aka 4800 *,N,1) is supported for easy plug and play communications with most GPS devices.

Here is a point by point summary.

The program will display a user-selectable icon on the main display at the coordinates reported by the GPS. On the image below, note the circle/box icon near the center of the image to the NW of the city of Chico. Note also the green  GPS  status indicator in the lower portion of the menu.

The user enables or disables GPS support in the Settings>Display Options dialog.

The main display has the text "GPS" in the button pane when the user has enabled GPS support.

  • If the text appears in red  GPS  then the GPS feature is enabled, but the program is unable to communicate with the device. See the Troubleshooting section for more information.
     
  • If the text appears in yellow  GPS  then the GPS feature is enabled and the program detects data on the serial port, but the data does not appear to conform to NMEA standards. This could mean that the device does not report the correct information or that the port settings are incorrect. See the Troubleshooting section for more information.
     
  • If the text appears in blue  GPS   then the GPS data is valid, but the device has not locked on to enough satellites to determine the location
     
  • If the text appears in green  GPS  then the GPS GPS feature is enabled and working normally, The program detects and is using GPS data from the serial port.
     

  • In normal operation the text will appear in RED or YELLOW when the program starts, until all of the history images have been obtained and any publication has been completed. Then, the GPS data will be polled and the status should change to BLUE or GREEN and the selected icon will be displayed.



It is normal for GPS devices to lose their satellite lock on occasion. Weather conditions, driving through tunnels or canyons, etc. can cause the GPS device to lose lock.
When this occurs, the status text will turn BLUE.  GPS
 

If this condition lasts for more than 5 seconds, the status text will begin to FLASH, notifying the user that the current icon location may not be correct.
When the GPS device regains lock, the status text will automatically return to GREEN.  GPS

You may unplug your GPS device from the computer at any time.
The status text will, in that case, turn RED.  GPS
When you plug the device back into the computer (be sure to use the same USB port), it will automatically recover and begin processing data.

IMPORTANT NOTE: it is critical that you plug the GPS device back in to the same USB port from which it was unplugged. If you plug it in to a different port, it may be assigned to a different COM port, and must be reconfigured as described below.

 



Configuring the GPS in StormPredator

Check your GPS device's software or use the Windows Control Panel's Device Manager to find out what COM port to which your GPS device is connected.
If you use the Device Manager, look for a USB-to-Serial device, and view its Properties to find the assigned port. Below is a screencap of the Windows 7 Device Manager dialog with the device for our preferred USB enabled GPS device shown configured as COM3. in the yellow highlight.



Other USB enabled GPS devices will show up in a similar way, once the device driver is correctly installed.

The GPS device ports are configured by pressing the Settings button on the main Storm Predator windows, then pressing Display for the "Display Options" dialog. To enable the GPS device, be sure the "Enable GPS Locator Device" box is checked.
 

Press the "Settings" button to the right of "Enable GPS Locator Device"



The port configuration and icon selection dialog appears.

Most off the shelf GPS devices have a default communications settings of 4800 Baud, 8 bits, no parity bit, and 1 stop bit (aka 4800 *,N,1) If needed, change the default settings to match your GPS device communications parameters and the COM port it is operating on.

Pressing the Browse button allows the user to select an icon for the GPS locator. Some special icons designed for use with GPS have been added with Version 3.5 and begin with the letter "z" which will be at the end of the list. But you can use any icon you wish for the GPS locator.



In the GPS configuration dialog, pressing the Test button will invoke a GPS serial port test.



Pressing the Start button initiates the test.
 


The output is verbose, and includes all data received from the port.


This is to allow users to troubleshoot potential problems.
For example, if the baud rate or parity is incorrect, garbled characters will appear.

The text scrolls indefinitely as data is received.

The test may be paused and restarted at will.
Pausing the test allows users to analyze the text in the display without it scrolling out of view.

If you see an error message stating that the handle is invalid, then the program cannot detect a GPS device connected to the specified port.
This may be because the device is unplugged, the wrong serial port was specified, or the serial port communications parameters are incorrect.



 


Troubleshooting and technical information

StormPredator supports all GPS devices that conform to NMEA (National Marine Electronics Association) standards and that also have a USB or serial data output.

For complete NMEA standards information and other technical information, please see the NMEA web site at www.nmea.org

You must install a USB-to-serial driver specific to your GPS device and connect the GPS device to the computer running StormPredator via a USB cable.
When those are installed, use the GPS's Windows application to get the port parameters, or refer to the Windows Control Panel's Device Manager to determine the port.

When you press the Test button in StormPredator's GPS configuration dialog, another dialog appears that displays the currently selected serial port settings.

Press the Start button to begin communicating with the port.
If you see garbled data, then something is wrong with the port settings.

Things that most commonly go wrong are incorrect baud or parity settings.
You may also have specified the wrong serial port.

Refer to your GPS device's documentation for more information about the correct settings for your device.

When the data begins streaming to the window, you will see something similar to the text below:

GPGGA,171210.000,3946.2079,N,12150.5915,W,2,11,1.0 ,67.1,M,-22.2,M,1.8,0000*7B
GPGSA,A,3,22,06,15,14,19,21,03,24,27,26,18,,1.8,1. 0,1.4*3E
GPRMC,171210.000,A,3946.2079,N,12150.5915,W,0.08,4 8.59,060410,,*25
GPGGA,171211.000,3946.2079,N,12150.5915,W,2,11,1.0 ,67.1,M,-22.2,M,2.8,0000*79
GPGSA,A,3,22,06,15,14,19,21,03,24,27,26,18,,1.8,1. 0,1.4*3E
GPRMC,171211.000,A,3946.2079,N,12150.5915,W,0.07,5 6.10,060410,,*29
GPGGA,171212.000,3946.2079,N,12150.5915,W,2,11,1.0 ,67.1,M,-22.2,M,0.8,0000*78
GPGSA,A,3,22,06,15,14,19,21,03,24,27,26,18,,1.8,1. 0,1.4*3E
GPRMC,171212.000,A,3946.2079,N,12150.5915,W,0.08,5 0.70,060410,,*25
GPGGA,171213.000,3946.2079,N,12150.5915,W,2,11,1.0 ,67.1,M,-22.2,M,0.8,0000*79
GPGSA,A,3,22,06,15,14,19,21,03,24,27,26,18,,1.8,1. 0,1.4*3E
GPGSV,3,1,12,22,74,308,31,18,56,047,34,26,54,071,4 0,06,51,267,32*7B
GPGSV,3,2,12,24,48,101,33,21,47,105,37,03,44,280,3 5,14,38,184,34*7A
GPGSV,3,3,12,19,28,311,34,27,15,069,32,15,07,038,3 6,16,02,231,*7B

Each line of this data is referred to as a "sentence"
StormPredator is only concerned with the GPRMC sentence.

This sentence contains all of the information we need to plot a marker and determine the status of the GPS device.

The lat/lon values are present in several NMEA sentences, but some of them are not included in some GPS devices.

The GPRMC sentence is almost universally provided by GPS devices.

Once you have data streaming that appears similar to the above, you can tell the test function to filter the data to display only the GPRMC sentences.
We recommend that you only use that feature to troubleshoot satellite communications problems between the GPS device and the GPS satellites.

You may press the Stop and Start buttons to pause the data for further analysis or for copying the data to the clipboard.

If you do not see lat/lon values in the GPRMC sentence, check the Satellite Fix Status word of the sentence.

If you see a "V" in that word, then the GPS has not "locked on" to enough satellites to determine the lat/lon of the GPS device.

See the technical description of the GPRMC sentence below for more information.

 




NMEA GPRMC Sentence Technical Information

All NMEA sentences begin with a dollar sign ("$").
The GPRMC sentence consists of twelve comma-delimited "words":

Example:
$GPRMC,040302.663,A,3939.7,N,10506.6,W,0.27,358.86 ,200804,,*1A

Descriptions:

Command Word
The command word indicates that the sentence is to be interpreted as a recommended minimum message.

Satellite-Derived Time
GPS devices are able to calculate the current date and time using GPS satellites (and not the computer's own clock, making it useful for synchronization). This word stores the current time, in UTC, in a compressed form "HHMMSS.XXX," where HH represents hours, MM represents minutes, SS represents seconds, and XXX represents milliseconds. The above value represents 04:03:02.663 AM UTC.

Satellite Fix Status
When the signals of at least three GPS satellites become stable, the device can use the signals to calculate the current location. The device is said to be "fixed" when calculations of the current location are taking place. Similarly, the phrases "obtaining a fix" or "losing a fix" speak of situations where three signals become stable or obscured, respectively. A value of "A" (for "active") indicates that a fix is currently obtained, whereas a value of "V" (for "inValid") indicates that a fix is not obtained.

Latitude Decimal Degrees
The latitude represents the current distance north or south of the equator. This word is in the format "HHMM.M" where HH represents hours and MM.M represents minutes. A comma is implied after the second character. This value is used in conjunction with the longitude to mark a specific point on Earth's surface. This sentence says that the current latitude is "39°39.7'N".

Latitude Hemisphere
This word indicates if the latitude is measuring a distance north or south of the equator. A value of "N" indicates north and "S" indicates south. This sentence says that the current latitude is "39°39.7'N".

Longitude Decimal Degrees
The longitude represents the current distance east or west of the Prime Meridian. This word is in the format "HHHMM.M" where HHH represents hours and MM.M represents minutes. A comma is implied after the third character. This value is used in conjunction with the latitude to mark a specific point on Earth's surface. This sentence says that the current longitude is "105°06.6'W".

Longitude Hemisphere
This word indicates if the longitude is measuring a distance east or west of the Prime Meridian. A value of "E" indicates east and "W" indicates west. This sentence says that the current longitude is "105°06.6'W".

Speed
This word indicates the current rate of travel over land, measured in knots.

Bearing
This word indicates the current direction of travel over, measured as an "azimuth." An azimuth is a horizontal angle around the horizon measure in degrees between 0 and 360, where 0 represents north, 90 represents east, 180 represents south, and 270 represents west. This word indicates that the direction of travel is 358.86°, or close to north.

UTC Date
GPS devices maintain their own date and time calculated from GPS satellite signals. This makes GPS devices useful for clock synchronization since the date and time are independent of the local machine's internal clock. This word contains two-digit numbers for days, followed by months and years. In the example above, the date is August (08) 20th (20), 2004 (04). The two-digit year is added to 2000 to make a full year value.

Magnetic Variation
This word denotes the magnetic variation from True North. This value varies by latitude and longitude. This word may not be included in some GPS models, as in the above example.

Checksum
The checksum is used to identify errors in the data which may have occurred during transmission. It is a simple accumulation of the total decimal ASCII values of each character in the sentence.