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For managing, manipulating and mapping GPS data

Frequently Asked Questions (FAQs)


  1. How do I test my communication port?
  2. My GPS has a serial cable interface, but my computer only has USB ports.
  3. The coordinates in GPS Utility differ from GPS values.
    What are Datums?
  4. How does GPS Utility deal with altitude information?
  5. Sometimes there is a difference of 1 in the last digit of a coordinate.
  6. I am having printer problems.
  7. Why do the eTrex (and eMap) tracks show a timestamp of 31-DEC-1989.
  8. Why do I not get the trackpoint creation time when I download tracks from my Magellan 315/320?
  9. What are Waypoints, Routes and Tracks?
  10. How can I upload maps to my Garmin receiver?
  11. Can I use GPS Utility to delete waypoints in my GPS?
  12. What is Selective Availability?
  13. I cannot import the 'intermediate' waypoints from AutoRoute Express / Streets and Trips.
  14. I cannot transfer data from 'Discovery Walking Guides' PNF CD to my GPS.
  15. I upload waypoints to my Garmin but they do not appear to be there in the GPS.
  16. I get an error on uploading Routes to my Magellan.
  17. When I download Waypoints from a Magellan 315, the download stops after a few waypoints.
  18. I have some data which is referenced to the wrong datum. How can I correct this?
  19. How do I get my Garmin Nuvi, Colorado, Oregon, Zumo or Edge705 to work with GPSU?


How do I test my communication port?

Do the following steps:

  1. Check that you have the correct port number set up in GPS|Setup...
  2. If you get a message saying 'Could not Connect ...' check that no other program is using the communication port. Check your Start up folder to see which other programs may be active and could have grabbed the port.
  3. Set the Interface mode to NMEA and click OK.
  4. Start the Interface Monitor from the GPS menu.
  5. Do GPS|Connect and you should see "CONNECTED to NMEA interface".
  6. Now set your GPS unit to transmit NMEA (if Magellan, then also make sure that it has a satellite view, is locked on and producing a position). You should now see incoming NMEA messages in the Interface Monitor. This tests that the basic connect and download wire are functioning correctly.
  7. If you suspect that the upload wire is not working, then create a TEST waypoint in a New window. Remove the GPS unit from the cable and then connect a short piece of wire between the Data-Out and Data-In pins (check your manual for the pins). This will loop any outgoing signal back as an incoming signal. Do GPS|Upload Waypoints and you should see the upgoing waypoint returned e.g:
    ->$GPWPL,0000.000,N,00000.000,E,TEST*5D
    Finished with Comms.
    <-$GPWPL,0000.000,N,00000.000,E,TEST*5D
    
    If this is successful then the cable and communications port would appear to be working. Remove the wire link and reconnect your GPS to the cable.
  8. Do GPS|Disconnect and select the correct interface mode for your GPS receiver (Garmin or Magellan). Set your GPS receiver to the correct transfer mode (e.g. GARMIN or GRMN/GRMN). Do GPS|About and you should a small panel with see some information relating to your GPS model.
  9. If you have been successful with the 'loop' test above, but still cannot get your GPS to work in Garmin or Magellan mode, then jiggle the connector at the GPS receiver end. The eTrex/eMap are particularly prone to having poor contacts between the cable and the receiver.
  10. If you suspect GPS Utility does not fully support your GPS then please send a note to the author containing the information given by GPS|About. It would also help if you saved the connect sequence interface trace by doing SaveAs... in the Interface Monitor and attaching the trace file to the email.

My GPS has a serial cable interface, but my computer only has USB ports.

To connect a GPS with a serial cable to a computer which only has USB ports you need to obtain a USB/Serial cable adapter, such as the "USB-Serial Cable Adapter" available from www.pfranc.com.

The cable comes with a software driver which you must install first. When you plug the cable into a USB socket on your computer, the software creates a virtual serial port within the computer to which GPSU can connect. Connect you GPS via its own serial cable to the adapter cable.

In GPSU, use the 'Check' button in the GPS|Setup.. dialog. This will tell which serial port numbers are available. Select that port which appears when you plug in the cable.

As an alternative to using the Check button, go to the Control Panel -> Performance and Maintenance -> System ->Hardware -> Device Manger -> Ports to see which virtual serial port your software has generated. Use this port number in GPSU|Setup...

It is possible that the port number may change on different bootups so you may need to check this.

In some cases it is not wise to boot-up the computer with the USB/Serial cable attached, as then the operating system may decide it is a mouse and not a GPS. Bootup first and THEN plug the cable in - that is once the operating system has completed its powerup sequencing and already found the mouse.

The coordinates in GPS Utility differ from GPS values.
    or:
What are datums?

This is usually because you have set different datums in GPS Utility and in your GPS receiver. Coordinate values are referenced to a particular datum and so when you change datums the coordinate values will change. The actual position does not change, it is just the distance from the "origin" that has changed. When you change datums you change the origin of the coordinate system that you are using.

Check which datum you have set in the GPS and which datum you have set in GPSU.

For more details, see Datums.

How does GPS Utility deal with altitude information?

Altitude can be referenced to any of:

  1. The WGS84 ellipsoid (a mathematically defined surface which forms the basis for GPS position calculations)
  2. A selected datum's ellipsoid (another mathematically defined surface - shifted with respect to the WGS84 ellipsoid, but usually defined to closely match the local surface of the Geoid for a geographic region).
  3. A Geoid (a surface of equal gravitational potential - caused by density variations within the earths crust)
  4. Mean Sea Level (slightly different from the Geoid surface, because of permanent ocean currents, winds, temperature and salinity differences)

Coordinate data transmitted using the Garmin protocol is transmitted in WGS84. If there is no height information, then the height is assumed to be zero on the WGS84 ellipsoid. If there is height information from the GPS, then this is assumed to be referenced to the ellipsoid of the datum which is currently set in GPSU. If you now display this data using some other datum, the altitude is referenced to that datum and you will see a value which represents the difference in height between the two datums (or ellipsoid surfaces).

Coordinate data tranmitted using the NMEA interface, is referenced to a user selected datum. GPS Utility ASSUMES that you have set the same datum as the GPS unit and displays the altitude as received over the interface without change.

GPS Utility displays the altitude as an 'ellipsoid' height. It does not have a 'geoid' height model which would account for local variations of the gravitational field. Mean Sea Level may differ from the the ellipsoid surface by a number of metres. Over a local area, this offset will be fairly constant.

You may like to read about the seven level headed scientists who can explain this much better.

See also:

As GPSU does not have a geoid model, you should set GPSU to the local datum before you download data from a GPS receiver. The geoid height and local datum height are normally very similar. If you need to re-reference or adjust the height information then you can use the Calibrate Altitude tool in GPSU.

Sometimes there is a difference of 1 in the last digit of a coordinate

Sometimes there is a difference of 1 in the last digit of a coordinate between the GPS receiver and GPS Utility. This is because the value that you see on the GPS is derived from an internal form. There are several mathematical transformations that need to be performed (datum conversion and grid projection) before the result is rounded to the nearest value. This might be to the nearest metre, so a value of 12345.51 would rounded to 12346.

If the internal form is then transmitted to GPS Utility, this may be quantised for transmission over the interface. When GPS Utility receives the quantised coordinate, it then performs the datum and grid transformations and then rounds the value for display. This rounding can result in a value that differs by +/-1 in the final digit from the value shown in the GPS.

I am having printer problems

You probably have a an out of date printer driver. This is usually the case when you have upgraded your operating system. Go to the printer manufacturer's website and see if there is a new printer driver for our printer, download and install it.

Hopefully this will fix the problem.

Why do the eTrex (and eMap) tracks show a timestamp of 31-DEC-1989

The eTrex records a timestamp for each trackpoint in the Active Log. However, when this is saved as a Stored Log, the timestamp is "stripped from a saved tracklog to reduce the amount of memory taken up" (according to Garmin). If you download a Stored Log, then the date is given as 31-DEC-1989 (GPS time zero). If you upload a track as an active log, then the timestamp is also set to the default value. Only an eTrex derived active track log contains valid time value.

Why do I not get the trackpoint creation time when I download tracks from my Magellan 315/320?

The original software as shipped with the Magellan 315/320 does not provide the trackpoint creation date and time in track download. GPSU defaults to the time at which the trackpoints were downloaded. Software version 3.12 (or later) obtainable from the Magellan website should fix this problem. You need to upgrade your 315/320 to the latest software version.

What are Waypoints, Routes and Tracks?

A Waypoint is a place or position with a defined coordinate and a name. For example, Your House, the Church, the road Junction, the Marina. A waypoint may have other attributes such as a Symbol (Icon), Height and Comment. Sometimes waypoints are refered to as Points of Interest (POIs).

A Route is an ordered lists of waypoint names. For example:

Marina ===> Church ===> Junction ===> House.
You might construct a route so that you can load it to your GPS in order to guide you when visiting each waypoint in order. A route may consist of say 3 to 50 waypoints - perhaps of the places you may wish to go to.

A Track is normally the recording of a previously traversed path. It consists of an ordered list of Trackpoints and shows where you have been. Each trackpoint has a position and a date/timestamp. Individual trackpoints do not have a name, but a whole Track may have a name. The GPS records trackpoints periodically - either every few seconds, few metres or automatically when the path deviates significantly from a predicted position (depends on the mode set in your GPS receiver). In some GPS receivers the tracks may be broken into track segments (there are breaks in the track, for example, when the GPS is powered off). A track may contain several hundred or even thousands of trackpoints.

In GPS Utility Waypoints, Routes and Tracks are shown in default colours. However, you can change these colours if you wish.
GPSU Panel

Tracks may show the detailed path between 2 waypoints, whilst a Route only shows the straight line path between 2 waypoints.

Warning: When a route is shown graphically by lines connecting the waypoints, the lines DO NOT INDICATE that the ground path actually follows a straight line. The connecting line only implies that two waypoints are sequential. Whilst a straight line indicates the general direction 'a bird would fly' between waypoints it may NOT BE SAFE TO FOLLOW THE LINE ON THE GROUND.

How can I upload maps to my Garmin receiver?

It is not possible to upload scanned image maps to a Garmin receiver.

Garmin software can upload vector maps (i.e. those consisting of drawn lines). However, Garmin have not published the interface protocol for uploading vector maps and so this function is not supported in GPS Utility.

The best you can do with GPS Utility is to create tracks which can be used as 'pseudo maps'. You can do this by digitising tracks using scanned maps - see the Help topics 'mapping' and 'digitising'. The maps are a bit crude, but it does work for some purposes.

Can I use GPS Utility to delete waypoints in my GPS?

Sorry, it is not possible to delete individual waypoints in your GPS from a PC. The workaround is to download all the waypoints, delete those you do not need, clear all waypoints in your GPS receiver and then upload those that you want to keep.

What is Selective Availability?

Selective Availability (SA) is NO MORE!

As of midnight on the 1st May 2000, SA was discontinued under orders of the President Clinton. Selective Availability was the purposeful degradation of the GPS signal for civilian users. This took the form of a timing 'jitter' in the signals coming from the satellites giving a slightly erroneous position (up to 100m for 95% of the time). The military could decode the signal correctly and remove the jitter. Without SA the error is about 15m horizontally and 25m vertically for 95% of the time.

I cannot import the 'intermediate' waypoints from AutoRoute Express / Streets and Trips.

The intermediate waypoints displayed in AutoRoute Express or Streets and Trips are NOT exported in the file - they are obtained when needed from the CD data base which is encrypted. Therefore they cannot be imported into GPS Utility.

If you want intermediate route waypoints, then you need to define them as 'Stop' or 'Via' points first. These are exported and can be read by GPS Utility into a route.

If you also capture the AutoRoute Express/Streets and Trips screen image, then you can calibrate this map image using your Start and End points and then you can quickly digitise the route as a track ready for upload to your GPS receiver. More information regarding this technique is available in Hints and Tips.

I cannot transfer data from 'Discovery Walking Guides' PNF CD to my GPS.

The "Personal Navigator Files" (PNF) files published by Discover Walking Guides contain only waypoint files (*.wpt) and track files (*.plt). The files do not contain any routes (in the Garmin or Magellan sense of this term).

The DWG PNF *.wpt files contain a set of waypoints which are in the correct route order. If you want to make a route in GPSU, then open the *.wpt file and check that the waypoints look right in the waypoint table view and in the map view. Do 'Record|Select All' and then 'Tools|Insert in Route'. From the Insert waypoint in Route dialog, select an empty route using the up/down arrow keys and then 'All'. Note: it is best not to choose Route 00. This will create a Route which you can see in the Route table view. Please note the warning shown in red regarding following routes in the Help topic in GPSU on 'Routes'.

The Freeware version of GPSU is limited to 5 Routes, each of a maximum of 10 waypoints per route. See the Help topic in GPSU on 'freeware' for details.

In GPSU if you open a *.plt file then it appears in the track table. However, the *.plt files may not have a track name and when such a file is opened in GPSU the track name is empty. Many Garmin GPSs REQUIRE that all tracks are named. To do this in GPSU go to the track summary table and double click on the track, then enter a name in the dialog.

Also see the Help topic in GPSU on 'Garmin Notes'->Tracks.

Please note that this these are limitations of the PNF files and are not a shortcoming of GPSU.

I upload waypoints to my Garmin but they do not appear to be there in the GPS.

When you upload waypoints to a Garmin they may not be visible in the waypoint table. This is usually because you have the Garmin waypoint find mode set to "Find by Nearest". In this mode, waypoints which are located some distance away from the current (or last known) position fix, will not be displayed.

Change the waypoint find mode to "Find by Name" and you should see them. - go to the Waypoint MENU to change the mode and/or check your manual on how to do this.

I get an error on uploading Routes to my Magellan.

When uploading a Route to a Magellan, if you get an error message similar to "Unable to load record. $PMGRTE ......", then this usually means you are trying to load a Route with more waypoints than the Magellan will accept. In some Magellan GPS receivers (e.g. 315, Explorer and SportTrack), the receiver then goes into a permanent error state which is difficult to clear (this is a bug in the Magellan GPS).

Usually the only way to clear it is to delete ALL routes in the Magellan and then try reloading the data. When you reload the data ENSURE that all routes do not contain more waypoints than is acceptable to the GPS (usually 30 waypoints).

When I download Waypoints from a Magellan 315, the download stops after a few waypoints.

Sometimes waypoints may become corrupted in a Magellan 315 and the only way to download them is to delete them in the Magellan itself.

For example, you may be able to download 8 waypoints OK and then an error occurs. In this case, try deleting the 9th waypoint in the Magellan and try again. This way you may get more waypoints next time. Alternatively, save the 8 waypoints you have already downloaded in a file and then delete those from the 315 and try for more. Hopefully in this way you will be able to recover most of your uncorrupted waypoints. If you manage to get all your waypoints downloaded, then do a memory reset in the Magellan 315 - clear memory of all routes and waypoints and then upload the waypoints again.

I have some data which is referenced to the wrong datum. How can I correct this?

To correct the data you need to 'fool' GPSU into accepting it with a different datum definition.

Open your file of data in GPSU. If not a GPSU file then save it in its current datum. Now switch the datum in GPSU to the correct datum and save the file again. You will now have 2 GPSU format files one in each datum. Open both files using a standard text editor and swap the 2 datum definition lines (the Lines beginning with 'M E'). between the files. Save the files from the text editor and then open in GPSU. One file will now be corrected and the other file will be twice as wrong. Discard the wrong file and keep the corrected file.

How do I get my Garmin Nuvi, Colorado, Oregon, Zumo or Edge705 to work with GPSU?

The Garmin Nuvi, Colorado, Oregon, Zumo and Edge 705 models do not support transfer of data via the PC interface as other Garmin models. Instead they behave as a removable media USB Mass storage device via the USB interface. To transfer data from/to these Garmin models, you use File|Open.... and File|SaveAs... and navigate to the folder containing the GPX files. When saving data, save as an *.gpx file (GPS Interchange file). See your Garmin manual regarding this.



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